Transactions from the Xth International Orthoptics Congress 2004

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Transactions from the Xth International Orthoptics Congress 2004

‘Global Perspectives Converge Downunder’

Transactions of the Xth International Orthoptic Congress

14-17 November 2004

Sydney Australia

Melbourne, Australia

Edited by: D.Verlohr, Z.Georgievski, A.Rydberg

and t Institution of Engineers, Australia.

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ISBN 187704024X. Transactions on CD-ROM of the Xth International Orthoptic Congress. © Copyright 2004 International Orthoptic Association.

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‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Table of Contents

Burian Lecture

Amblyopia

Binocular Vision

Eye Movements

Low Vision

Neuro-Orthoptics

Ophthalmic Technology & Vision Science

Paediatric Ophthalmology

Professional Development & Education

Public Health Agenda & Screening

Strabismus - Concomitant

Strabismus - Incomitant

Strabismus Surgery

Symposia - AAPOS: Childhood Blindness Worldwide

- ISA: Update on Chemical (or Pharmacological) Treatment

for Strabismus

- Vision Screening: Critical Appraisal of the Evidence in

Favour (or not...!) of Vision Screening in Children

Workshops

Clicking on the items below

will take you to the document

= Abstract

= Full Paper

Oral presentations in black

Posters in blue


‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Burian Lecture

Factors Contributing to the Outcome of Sensory Testing in Patients with Anomalous Binocular Correspondence — Kyle

Arnoldi (USA)


‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Amblyopia

Steady-State Sweep VEP Acuity in Childhood Amblyopia: A Longitudinal Prospective Treatment Study - Arvind

Chandna, S.I.Chen, A.M.Norcia, D.Stone (UK / USA)

Snellen, Sheridan Gardiner and Lea Symbols Acuity: A Comparative Study - Arvind Chandna, J. Senior, L.Bell

(UK)

Recovery of Contour Integration Thresholds in Relation to Logmar Visual Acuity during Treatment of Amblyopia

in Children -Arvind Chandna, A.M.Norcia (UK / USA)

A National Survey of the Use and Range of Written Guidance for Occlusion in the Treatment of Amblyopia - Sue

Elliott (UK)

Amblyopia: 'Is there more to Amblyopia Treatment than Meets the Eye?'-Sahira Hanif, C. Noonan (UK)

The Psychosocial and Functional Impact of Amblyopia and its Treatment -Konstandina Koklanis, L.Abel, R.Aroni,

J.E.Elder (Australia)

Atropine Occlusion-How Long Does it Take for Fixation to Swap? - Rowena McNamara, P.Rice (UK)

Factors Predicting Non-Compliance with Occlusion Therapy for Amblyopia: Results from the Electronic

Recording of Patching for Amblyopia Study (ERPAG) - E.van Minderhout, S.E.Loudon, B.Simonsz, M.V.Joose,

M.Fronius, M.Awan, D.Newsham, R.A.Harrad, H.J.Simonsz (The Netherlands/Germany/UK)


‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Inventory of 404 Orthoptists Simultaneously Prescribing Occlusion Therapy for Five Sample Amblyopic Cases -

Janine Monique Van Zon, R.Delle Site, S.E.Loudon, J.R. Polling, B.Simonsz, H.J.Simonsz (The Netherlands)

Evaluation of Reading Using Mnread-Jk with Normal Children and Anisometropic Amblyopia Children — Kazuyo

Ohmure, Fumiko Matsumoto, Akemi Wakayama, Kiyo Ohmura, Toru Kusube, Kosuke Abe, Masayo Kinoshita,

Yoshikazu Shimomura (Japan)

II. Electronic Recording of Patching for Amblyopia Study (ERPAG): Can Compliance be Improved? — Brigitte

Simonsz, S.E.Loudon, M.V.Joosse, M.Fronius, M.Awan, D.Newsham, R.A.Harrad, H.J.Simonsz (The

Netherlands / Germany / UK)

Longterm Outcome of Occlusion Therapy for Amblyopia in a Historic Cohort —Brigitte Simonsz, H.Van Kempen,

E.S.van de Graaf, G.W. van der Sterre, H.J. Simonsz (The Netherlands)

Spatial and Temporal Distortions in Strabismic Amblyopia - Ruxandra Sireteanu, C.Baumer, C,Sarbu, S.Tsujimura

(Germany)

An Electrophysiological Study of Magnocellular and Parvocellular Visual Function in Early and Late Onset

Strabismic Amblyopia —John Sloper, A.Davis, M.Neveu, C.Hogg, M.Morgan, G.Holder (UK)

Optimisation of the Dose-Response of Occlusion Therapy for Amblyopia: The ROTAS Study — Catherine Stewart,

M.J.Moseley, D.A.Stephens, A.R.Fielder (UK)

Treatment Dose-Response for Amblyopia: Results from the MOTAS Study —Catherine Stewart, Merrick Moseley,

David Stephens, Alistair Fielder (on behalf of the MOTAS Cooperative) (UK)


‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Evaluation of Diagnostic Usefulness of the Simultaneous Foveal Perception Test in Assessment of

Anisometropic Amblyopia — Sachiko Takamura, K.Matsuda (Japan)

Treatment of Amblyopia in Japan — Chie Usui, T.Hayashi, M.Minoda, S.Kawano (Japan)


‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Binocular Vision

Range of Accommodation and Binocular Vision after Refractive Surgery — Jeroen Claeys, D.Godts, R.Trau,

M.J.Tassigno (Belgium)

Assessing the Dominant Eye - A New Method to Determine Sensory Dominance during Binocular Vision —Elaine

Cornell, C.Emmanouilidis, N.Moss (Australia)

Does Dissociation Reduce Stereoacuity? —Helen Davis, Michelle Tewkesbury, Jonathan Dominic, John P Frisby,

David Buckley (UK)

Does Stereoacuity Correlate with Interpupillary Distance for Normal Observers? - John P.Frisby, Emma Patchick,

Rebekah Edgar, Helen Davis (UK)

Assessment of Sensory Ocular Dominance —Junko Fujita, Takahiro Niida, Kazuo Mukuno (Japan)

The Age-Related Decline in Stereopsis as Measured by Different Stereotests — Louise Garnham, J.Sloper (UK)

A Clinical Quantitative Measurement of Ocular Dominance —Tomoya Handa, Hiroshi Uozato, Kazuo Mukuno,

Takahiro Niida, Nobuyuki Shoji, Risako Higa, Marie Nitta, Kimiya Shimizu (Japan)

Can Stereo Tests be an Indicator of Decreased Visual Acuity? — Toshie Hirai, Keisuke Takahashi, Yoshikatsu

Kawase, Muneko Tanabe, Norio Ohba (Japan)


‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress

Stereoacuity Following Unilateral and Bilateral Cataract Extraction — Rebekah Lawry (UK)

Measurement and Improvement of Visual Skills in Young Adults — Yoshie Morita, Akiko Toshimitsu, Mitsuko Shima,

Maureen Powers (USA / Japan)

Diagnosis and Treatment in Patients with Asthenopic Symptoms Due to Exophoria — Birgitta Neikter, Brigitte

Eriksson-Derouet (Sweden)

Monovision by Implanted Intraocular Lenses — Marie Nitta, Takahiro Niida, Risako Higa, Kimiya Shimizu (Japan)

The Effect of Simulated Torsional Disparity on Horizontal Fusional Vergence and Stereopsis in Normal Subjects

— Michael Sleep, Z.Georgievski (Australia)

Strabismus In Childhood: Unilateral Cataracts Function Of Age At Surgery (About 75 Cases). — Dominique

Thouvenin, C.Lesage, S.Nogue, L.Fontes, O.Norbert, J.L.Arne (France)

The Use of a Computerised System for the Study of Binocular Vision: First Experiences — Joy White, Hector

Rojas-Anaya, L.Ripley (UK)

Disruption of Binocular Vision following Cataract Surgery — Joy White (UK)


The Burian Memorial Lecture:

Factors Contributing To The Outcome Of Sensory Testing

In Patients With Anomalous Binocular Correspondence

Kyle Arnoldi, CO

Department of Ophthalmology, State University of New York at Buffalo

The Women and Children’s Hospital of Buffalo

Buffalo, New York, 14222 U.S.A.

kylea@buffalo.edu

Abstract

Traditional teaching on ARC identifies the dissociative quality of a sensory test as the primary

factor influencing the outcome of retinal correspondence testing. However, these tests differ also

in function and format. This study compared one mildly dissociating test and one highly

dissociating test to evaluate the subjective visual direction of both the deviation point and the

fovea of the deviating eye in 74 patients with ARC.

Subjects were more likely to demonstrate an ARC response, and to do so after a

significantly shorter period of time following change in alignment, on the minimally dissociating

tests. However, 7% demonstrated ARC only on a highly dissociating test. 85% demonstrated the

presence of a pseudo-fovea, while only 39% had evidence of rewiring of the deviated fovea. The

mean angle of deviation of the latter was significantly larger than that of the former group

(p


masking of the innate underlying normal sensory relationship.(4) The perceived inconsistency of

responses on correspondence tests has been interpreted as a measure of the depth or severity of

the cortical adaptation, which is believed to be a function of the length of time it has been

present.(5) Sensory tests are therefore stratified according to the degree to which they alter the

perception of the normal binocular visual environment.(6)

However, the standard tests of retinal correspondence differ not only in degree of

dissociation, but in function and format.(3) Some tests are designed to determine if the deviation

point has acquired a common visual direction with the fovea of the dominant eye, (fovea-toperiphery

tests), while others directly determine the localizing value of the anatomic fovea of the

deviating eye (fovea-to-fovea tests). Still others are capable of evaluating both retinal points.

Testing formats vary from anaglyphic, to Polaroid, to after-image, to haploscopic methods. In

spite of these dissimilarities, sensory tests tend to be compared directly, as if equal in all qualities

except for degree of dissociation. In overlooking these important differences between tests, we

may have dismissed valuable information on the visual sensory system as testing artifact.

The purpose of this study was to determine what effect the retinal element examined

(deviation point vs. fovea of the non-dominant eye) may have on the results of correspondence

testing, while controlling for degree of dissociation and test format. The answer to this question

may reveal clues to the wiring strategy of the visual cortex in the presence of a manifest

deviation, and hint at the anatomical substrate of ARC.

Methods

Consenting patients with manifest strabismus of ≥ 8Δ and an ARC response documented on a

prior orthoptic exam were studied prospectively. Excluded were those with intermittent

strabismus, evidence of eccentric fixation, and those with fusional vergence amplitudes. Also

excluded were those incapable of reliable subjective responses, including those with neurological

or developmental delay.

All subjects were tested with the Bagolini striated glasses at 33 cm in a well lit room

(fovea-to-periphery, minimally dissociating test). The Bagolini test was repeated with prism

offset of the deviation (fovea-to-fovea, minimally dissociating test). Following this, patients

were tested with the Worth 4-dot test at 33 cm (fovea-to-periphery, highly dissociating test) and

repeated with prism offset (fovea-to-fovea, highly dissociating). When applicable, refractive

correction was worn for sensory testing. Subjects who reported an anomalous fusion response on

the Bagolini (i.e. two diagonal lines intersecting to form a 90º angle at the point of the light

source to form an ‘X’) or Worth test (i.e. 4 lights) were interpreted as having a “pseudo-fovea” at

the deviation point. Those reporting paradoxical diplopia with prism offset of the deviation on

the Bagolini (i.e. 2 lights, each with a diagonal streak through it, forming an ‘A’ or ‘V’) or Worth

(5 lights) were assessed as having re-wired the anatomic fovea of the deviating eye so that it no

longer retained the “straight ahead” visual direction under binocular conditions.

In addition to the above testing, the following data were recorded: visual acuity using

linear optotypes, prism and alternate cover test in the primary and secondary positions of gaze at

6 m and 33 cm, and age of the patient at the test visit. Data gathered retrospectively from the

medical record included the age of onset of the strabismus, the length of time the patient has been

within 5Δ of the current angle of strabismus, and the age at which ARC was first documented on

exam.

2


Results

Seventy-four patients fulfilled the inclusion criteria and consented to participate in the study. The

mean age of the group was 15.5 ± 2 years (range 4 – 70 yrs.). The presence of ARC was

confirmed by amblyoscope or after-image test in 37%. Ninety-three percent of study patients

reported an ARC response on at least one of the two variations of the Bagolini Test, compared to

only 62% on the Worth Test. Forty-seven percent demonstrated ARC on both tests, another 46%

showed ARC with the Bagolini glasses only, and 7% reported an ARC response on the Worth 4-

dot only.

Study participants were more likely to test positive for ARC using one of the fovea-toperiphery

tests than the fovea-to-fovea versions of the Bagolini or Worth. Overall, 85%

demonstrated a pseudo-fovea, while only 39% had evidence of rewiring of the anatomical fovea

of the deviating eye. Table 1 illustrates that subjects who had acquired a pseudo-fovea tended to

have the smallest deviations. Those whose fovea had acquired a new visual direction tended to

have significantly larger deviations (p < .001). A rewiring of both retinal elements was relatively

rare, regardless of test used, and was found in patients with moderate angles of strabismus.

Table 1. Outcome of Correspondence Testing in 74 Patients with Anomalous Retinal Correspondence

With

Bagolini

With

Worth

With Both

Tests

Mean Deviation

At 33 cm

Pseudo-fovea

Only 25 (34%) 3 (4%) 22 (30%) 12 ± 2Δ

Rewired Fovea

Only 1 (1%) 5 (7%) 10 (14%) 30 ± 3Δ

Rewired Both

Retinal Elements 7 (9%) 2 (3%) 4(5%) 18 ± 2Δ

Rewiring of

Neither Retinal

Elements

5 (7%) 28 (38%) 0 (0%) 15 ± 2Δ

Subjects with angles of deviation within 14 prism diopters of orthotropia were

significantly more likely to acquire a pseudo-fovea, while retaining the visual direction of the

deviating fovea (p < .005). Ninety-seven percent of patients with strabismus ≤ 14Δ tested

positive for a pseudo-fovea, but did not rewire the fovea of the deviating eye. Eighty-nine

percent of those with angles larger than ET 20Δ or XT 15Δ rewired only the fovea of the

deviating eye, without developing a pseudo-fovea. Patients who rewired both the point of

deviation and the anatomic fovea tended to fall within a narrow intermediate zone between

esotropia 15 to 20Δ, and exotropia 10 to 15Δ (Fig. 1).

3


Fig. 1 Magnitude and Direction of Strabismus vs. Pattern of Rewiring in Patients with ARC

Temporal Retina

Nasal Retina

Fovea of deviating eye

Optic Disc

-30 -20 -10

+10 +20 +30

Only deviation point rewired

Only fovea rewired

Both points rewired

Only those deviations between XT 15 and ET 20 are compatible with a pseudo-fovea. Nasal

retina, and the corresponding areas in the visual cortex, appears capable of acquiring fusion

with the non-corresponding point in the dominant eye over a wider range of deviations than

temporal retina. The deviating fovea is more likely to “rewire” in large angles of strabismus.

Mean visual acuity in the dominant eye was .9 ± .02 (20/22 or 6/7), compared to .7 ± .04

(20/30 or 6/9) in the deviating eye. This is statistically different (p < .001). Amblyopia was

found in 44% of cases. Visual acuity appears to have no effect on the pattern of rewiring.

Specifically, decreased acuity is not associated with rewiring of the fovea of the deviating eye (p

> .3).

ARC is more common in esotropia, than in exotropia or hypertropia. Seventy-four

percent of the study patients were esotropic, 19% exotropic, and only 7% hypertropic. The mean

angle of strabismus for esotropic patients was 19 ±

Fig. 2 Direction of Deviation vs.

Pattern of Rewiring

% of Patients

80

70

60

50

40

30

20

10

0

Pseudofovea

Rewired

Fovea

ET

XT

Esotropes were more likely to acquire a pseudofovea,

while exotropes were more likely to

rewire the deviating fovea (p .5),

esotropes and exotropes developed different

patterns of ARC. Fig. 2 illustrates that esotropes

are more likely to acquire a pseudo-fovea than to

rewire the deviating fovea. The exotropic patient

was as likely to develop a pseudo-fovea as to

rewire the fovea. Exotropes are significantly more

likely to rewire the fovea than esotropes (p <

.005).

All study patients had onset of strabismus

during the first 10 years of life. The oldest age at

onset of a new strabismus that resulted in ARC

was 6 years. This esotropic patient rewired both

retinal elements on both tests within 8 months of

onset of the strabismus. The oldest age at which

ARC was noted for the first time in a patient with

longstanding strabismus was 15 years of age. This

patient first had surgery for a large angle infantile esotropia at age 12 years. In the years prior to

surgery, she repeatedly demonstrated dense alternating suppression on all sensory tests. Within

4


three years of surgical alignment, she began to report a pseudo-fovea on the Bagolini Test. The

oldest age at which a pre-existing ARC modified to adapt to a new deviation following

strabismus surgery was 17 years (2 patients). ARC was confirmed at a younger age in both

Fig. 3 Magnitude of Exodeviation vs.

Time to ARC Response

30

Time in months

25

20

15

10

5

0

0 10 20 30 40 50

Exotropia in prism diopters

The larger the angle of exotropia, the longer it

takes to develop ARC (r = .81).

cases, and a new anomalous correspondence

developed within 3 months of surgery.

For the group as a whole, the mean

length of time needed to rewire a pre-existing

ARC following a change in the deviation was

7.7 ± 1 months (range 2 – 24 months). There

was no correlation between the age of the patient

at the time of surgical alteration in the strabismic

angle and the length of time needed to adjust the

ARC to the new angle (r = .01).

Mean time needed to rewire was more

closely correlated with magnitude and direction

of strabismus. Esotropic deviations took an

average of 6.3 ± 1 months to adapt, while

exotropic deviations required a mean 15.5 ± 3

months. This difference is significant (p <

.0025). There was a weak positive correlation

between the magnitude of esotropia and time to new correspondence (r = .31), but a very strong

positive correlation between the severity of exotropia and time needed to rewire (r = .81) (Fig. 3).

Patients tended to demonstrate evidence of ARC on Bagolini glasses after a mean 7 ± 2

months, compared to 12 ± 2 months for the Worth 4-dot (p < .01). The mean time needed to

rewire the point of deviation was 6 ± 1 months, while it took an average of 10 ± 2 months to

rewire the fovea, regardless of test used (p < .05). The disparity in time needed to rewire the

fovea is more pronounced on the Worth test than the Bagolini (p < .02).

Discussion

This study compared one mildly dissociating test and one highly dissociating test of retinal

correspondence to evaluate the subjective visual direction of both the deviation point and the

fovea of the deviating eye. Results provide clear evidence in support of earlier studies

concluding that the greater the similarity of the images received by the two eyes, the easier it is

for the visual system to achieve anomalous fusion. In this study, subjects were more likely to

demonstrate an ARC response, and to do so after a significantly shorter period of time, on the

minimally dissociating tests. However, the 7% who exhibited ARC on the Worth 4 dot, and not

on the Bagolini test, clearly defy the classic teaching on the effect of dissimilar retinal images on

fusion ability. A previous study has also shown that, contrary to traditional thought, it is possible

to show ARC on a highly dissociating test, without expressing ARC on a minimally dissociating

test.(3) It appears then, that dissociation is not the only factor that determines sensory test

results. According to this study, the other variables that appear to impact the outcome include:

(a) retinal element evaluated (fovea vs. deviation point), (b) magnitude of the deviation, (c)

direction of the deviation (ET vs. XT), and (d) age of onset of the strabismus.

Retinal Element Evaluated. It has been thought that all retinal elements of the strabismic

eye between the deviation point and the fovea simultaneously rewire to correspond with the

fixating eye.(1) If this were the case, testing the directional value of any single point within that

range, or detecting fusion in the presence of a manifest strabismus, would be sufficient to prove

5


ARC. In this study, 89% of subjects rewired either the fovea or the deviation point, but not both

simultaneously. Although ARC most commonly manifested as the presence of a pseudo-fovea,

22% of patients in this study showed ARC only on a fovea-to-fovea test. All would have been

misdiagnosed had the Bagolini or Worth tests been performed only in the standard fashion. What

these results suggest is that the visual system selectively chooses certain points to rewire,

presumably based on a maximum visual benefit for minimum effort strategy, rather than rewiring

all retinal points simultaneously. The rewiring scheme becomes clearer when we compare the

deviations of those patients with and without a pseudo-fovea.

Magnitude of the Deviation. Subjects whose visual system rewired only the fovea had a

significantly larger angle of deviation, more than twice that of those who developed a pseudofovea.

Most studies of anomalous correspondence have found psychophysical and anatomical

evidence of ARC limited to moderate angles of strabismus, presumably due to the increased

distance axons would have to bridge in order for the non-corresponding neurons to

communicate.(7,8) In large angle strabismus, the resolution of the deviation point may be so

poor, and the distance that the cortical axon terminals would be required to span is so large, that

the resulting crude binocular vision would not warrant the expenditure of energy and time needed

to make such disparate points correspond. Similarly, the deviating fovea would have not only

superior resolution to the peripheral point in the fixating eye that is now receiving the same

image, but an overwhelming advantage in the volume of nerve tissue along the pathway

dedicated to analyzing its contribution to visual perception. Perhaps even deep suppression is not

enough to prevent the deviating fovea from disrupting visual input in these cases, thus warranting

the effort needed to alter its subjective visual direction.

However, it is also possible that what is occurring with the fovea of the deviating eye in

cases of large angle strabismus is an entirely different process: a rearrangement of the spatial

localization of that point, rather than a new anomalous connection between disparate points.

Most popular clinical tests used to evaluate the deviating fovea are not designed to determine

whether it is capable of fusion with the peripheral point in the dominant eye. True binocular

interaction, indicating a correspondence with the fellow eye, could be studied in patients with a

rewired fovea using steady-state VEP. Such a method has been successfully used to confirm

binocular interaction in patients with ARC in the form of a pseudo-fovea on Bagolini glasses.(9)

Direction of the Deviation. Esotropes were more likely to acquire a pseudo-fovea than

exotropes, and to do so in a shorter period of time. The retinal image zone that allows for the

development of a pseudo-fovea extends 5Δ further onto nasal retina than on the temporal side of

the fovea. Previous clinical studies have confirmed a higher quality of binocular vision in

esotropic patients with ARC.(10) It appears that esotropic patients acquire a higher grade of

binocularity in a shorter period of time, even with larger angles of strabismus.

What gives esotropes such an advantage? Anatomical studies of the sensory visual

pathway suggest that images projected onto temporal retina are at a competitive disadvantage,

even in the normal visual system. For example, cones and ganglion cells are 1.5 times less

numerous in the temporal retina than the nasal retina.(11) Layers of the lateral geniculate nucleus

receiving input from the ipsilateral temporal retina have fewer cells with less volume than those

receiving nasal retinal input.(12) Ocular dominance columns receiving temporal retinal input

occupy less territory than nasal columns in the visual cortex, and this disparity increases

dramatically with increasing retinal eccentricity.(13) PET scans have confirmed less metabolic

activity in cortical areas corresponding to temporal retina.(14) Psychophysical testing has

demonstrated that spatial resolution and vernier acuity are poorer in the temporal retina of normal

eyes.(15) And in patients with strabismus, suppression tends to be deeper for stimuli projecting

6


onto temporal retina, regardless of the direction of the strabismus.(16-18) Exotropic patients may

be at a disadvantage when it comes to rewiring the deviation point, simply because the input from

the nasal retina, particularly between the fovea and the optic disc, is given anatomical and

physiological priority in the visual pathway.

Onset of the Strabismus. It is thought that the potential to adapt binocular correspondence

is only present during the critical period, a stage of acute mutability in the developing visual

system usually thought to encompass the first decade of life. Further, it is believed that once

learned, the ability to shift correspondence is retained throughout life.(1, 5) Results of this study

suggest that what determines capability of adaptation is not the age at which ARC first develops,

but the age at which one develops a constant strabismus. Onset of strabismus during the critical

period may reset the developing binocular system, preserving a plasticity that allows for the

future development of ARC, should the prevailing conditions allow.

In the primary visual cortex of the non-strabismic patient with normal correspondence,

binocular processing first occurs in the superficial and deep layers of V1, after the initial stage of

processing in layer 4.(19) In the patient with early-onset strabismus, however, the cells in the

primary visual cortex become selectively monocular. Even a brief period of constant

misalignment early in the critical period is sufficient to significantly reduce the number of

binocular cells in V1.(20) With the loss of binocularity in V1, the site of convergence of sensory

input is transferred to the secondary visual cortex, where enlarged receptive fields can be more

forgiving of a lack of correspondence.(8, 21-22) It has also been shown that the critical period

for the higher levels of visual processing is more plastic and remains so for a longer period of

time than lower visual functions.(23) Relocating the anatomical site of fusion to the secondary

visual cortex may extend the period of plasticity, and allow for the development of ARC at older

ages. The upper age limit for a new onset of ARC is not known, but the results of this study

suggest that patients with early onset strabismus are capable of developing ARC for the first time

as late as the mid-teenage years.

Acknowledgements

The author would like to thank Marlo Galli, C.O., and Claire Castleberry, C.O. for their

invaluable help in gathering the patient data for this project.

References

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15. Fahle, M. (1983) Nasotemporal asymmetry in visual hyperacuity. Investigative Ophthalmology and Visual

Science Supplement, 24: 146.

16. Fahle, M. (1987) Naso-temporal asymmetry of binocular inhibition. Investigative Ophthalmology and Visual

Science, 28: 1016-1017.

17. Sirenteanu, R. (1982) Binocular vision in strabismic humans with alternating fixation. Vision Research, 22: 889-

896.

18. Sirenteanu, R, Fronius, M. (1982) Naso-temporal asymmetries in human amblyopia: Consequence of long-term

interocular suppression. Vision Research, 21: 1055-1063.

19. Boothe, R.G. (2002) Perception of the Visual Environment (pp. 262-274). New York: Springer.

20. Sireteanu, R., Singer, W., Fronius, M., Greuel, J.M., Best, J., Fiorentini, A., Bisti, S., Schiavi, C., Campos, E.

(1993) Eye alignment and cortical binocularity in strabismic kittens: a comparison between tenotomy and

recession. Visual Neuroscience, 10: 541-549.

21. Daw, N.W. (1995) Visual Development (pp.117-119). New York: Plenum Press.

22. Sirenteanu, R., Best, J. (1992) Squint-induced modification of visual receptive fields in the lateral suprasylvian

cortex of the cat: Binocular interaction, vertical effect and anomalous correspondence. European Journal of

Ophthalmology 4: 235-242.

23. Daw, N.W. (1994) Mechanisms of plasticity in the visual cortex. Investigative Ophthalmology and Visual

Science. 35: 4168-4179.

8


Range of accommodation and binocular vision after refractive

surgery

Jeroen Claeys, Daisy Godts, Ren Trau, Marie-Jos Tassignon

University Hospital Antwerp, Department of Ophthalmology

Wilrijkstraat 10

Edegem, Belgium

Jeroen.claeys@uza.be

Abstract

Purpose: To evaluate the effect of refractive surgery on accommodation and binocular vision

in patients without manifest or intermittent strabismus.

Material and methods: Fifty eyes of 25 patients were operated with laser subepithelial

keratomileusis technique (LASEK). Twenty-one patients were myopic, four patients were

hypermetropic. All patients had a complete orthoptic examination before and after refractive

surgery, including assessment of visual acuity, binocular function, ocular motility, near point

of accommodation and convergence.

Results: None of the patients presented changes in eye position, ocular motility, fusion,

stereopsis and convergence. In 30% of the patients accommodation decreased, in 16% it

increased.

Conclusion: In our study refractive surgery does not alter binocular vision and ocular motility.

Accommodation may change in a number of patients.

Keywords

Binocular vision, accommodation, refractive surgery, orthoptics, LASEK.

Introduction

Patients who underwent refractive surgery may have a variety of complaints such as blurred

vision, reading problem, halos, dominance problem or diplopia (1-2). The aim of this

prospective study is to find out wether accommodation or binocular vision is involved in

these complaints or not.

Material and Methods

Fifty eyes of 25 patients were operated with LASEK between February 2002 and July 2004

and were analysed. The age of the patients ranged between 23 and 54 years (mean age 40.36

years). The laser used, was a Broad beam Gaussian delivery system of InPro.

Twenty-one patients were myopic and four patients were hypermetropic. A complete

ophthalmological examination, including best-corrected visual acuity (BCVA), manifest and

cycloplegic refraction, anterior and posterior segment evaluation, intraocular pressure (IOP),

ultrasonic pachymetry, pupillometry and corneal topography was performed. All patients had

a complete orthoptic examination before and 6 weeks after refractive surgery. The ocular

alignment was measured with the alternate prism cover test (APCT) at 6m and 33cm and in

the synoptophore. The ocular motility was evaluated with the alternate cover test in the nine

directions of gaze. Fusion range was measured at distance and at near with the prism bar and

in the synoptophore. Stereoacuity was measured with the Titmus stereo test. Near point of

1


accommodation and convergence were measured with the R.A.F. near point rule, using pushup

method.

The follow-up ranged from 2 months till 30 months (mean 1.12 months). All patients were

no-risk patients as defined by Kowal (3).

Results

The refractive error improved in all patients. None of the patients lost visual acuity. Pre and

postoperative refractive error and visual acuity are summarized in table 1. Group 1 are

patients with refraction error between 0.00 and —3.00, group 2: between -3.25 and —6.00,

group 3: between -6.25 and —10.00 and group 4: between 0.00 and +3.00.

Table 1

Patient Preoperative refractive error Postoperative refractive error Preoperative

BCVA

Postoperative

BCVA

Group 1 RE LE RE LE RE LE RE LE

D.K. -200 -0.25x100 -2,00 -0,25x110 +0,25 -0,75x137 -0,25 -0,25x46 20/20 20/20 20/20 20/20

S.B. -1,25 -0,75 x5 -1,25 -0,25x0 +0,50 -0,50x160 +0,25 20/20 20/20 20/20 20/20

V.B. -3,00 -3,00 -0,25 -0,50x45 -0,75 -0,25x0 20/20 20/20 20/20 20/20

V.M. -1,00 -2,00 +0,25 -0,50x73 +0,25 -0,25x50 20/20 20/20 20/20 20/20

D.I. -1,50 -1,50 0,00 -0,50 20/20 20/20 20/20 20/20

S.C. -2,50 -2,75 +0,50 -0,25x170 0,00 20/20 20/20 20/20 20/20

D.M. -2,00 -1,00x180 -1,75 -0,75x180 +1,00 -0,75x150 +0,25 -0,25x85 20/20 20/20 20/20 20/20

W.M. -1,50 -0,50x180 -2,00 -0,50x40 -0,50 20/20 20/20 20/20 20/20

V.G. -3,00x105 -1,00 -0,50x90 +0,25 -1,25x100 -0,25 -0,25x35 20/25 20/20 20/20 20/20

Mean

values -1.92 -1.97

Group 2

-0.03 -0.13

M.C. -4,25 -3,50 -0,25X50 -0,25 -0,50x170 +0,25 -0,50x25 20/20 20/20 20/20 20/20

R.E. -4,5 -0,25x175 -4,75 -1,00 -0,25x0 -0,50 20/20 20/20 20/20 20/20

D.R. -3,50 -1x170 -3,50 -1,00x5 +0,50 -0,25x105 +0,50-0,50x150 20/20 20/20 20/20 20/20

M.V. -4,25 -3,50 -0,50x95 -0,25 -0,25x0 +0,25 -0,25x65 20/20 20/20 20/20 20/20

N.A. -4,00 -0,75x180 -4,25 -1,00x160 -0,75 -0,50x0 -0,50 -0,25x150 20/20 20/20 20/20 20/20

V.M. -5,50 -1,00x180 -5,00 -2,00x160 -0,75 -0,75x130 -0,75 -0,75x70 20/20 20/22 20/20 20/20

D.J. -2,00 -3,25x105 -2,00 -2,75x85 +0,50 -1,25x135 -1,00x40 20/30 20/25 20/30 20/30

B.M. -5.25 -0.50x155 -4.50 -0.25x45 -0.75 -0.25x140 -0.50 -0.25x60 20/20 20/20 20/20 20/20

Mean

values

Group 3

-4.53 -4.34 -0.5 -0.34

S.M. -6,75 -0,25x170 -6,25 -0,75 -0,25x0 -0,50 -0,50x15 20/20 20/20 20/20 20/20

V.F. -6,25 -1,25x20 -5,25—1,00x170 -0,75 -0,50x10 -0,75x35 20/20 20/20 20/20 20/20

G.T. -8,00 -8,00 -0.5x180 -1,25 -1,00 -0,5x20 20/20 20/22 20/22 20/22

Y.W. -8,00 -2,00x180 -7,00 -2,00x180 -1,00 -1,00x165 -0,75x10 20/25 20/22 22/25 20/22

Mean

values -7.63 -7.06

Group 4

-1.13 -0.69

P.M +2.25-0.50x135 +2.75 -0.25x65 +0.25 -0.50x100 +0.50 -0.25x80 20/20 20/20 20/20 20/20

V.J. +3,50-0,50x105 +3,50 -0,25x84 +0,75 -0,25x90 +0,50 -0,50x80 20/20 20/20 20/20 20/20

K.C. +2,00 +1,50 +0,25 -0,25x0 20/20 20/20 20/20 20/20

L.H. +1,25 -0,50x90 +0,75-0,25x115 -0,50 -0,50x85 -0,50x45 20/20 20/20 20/20 20/20

Mean

values +2.06 +2.06

+0.03 +0.06

No change in ocular alignment and ocular motility was measured. Binocular function

remained the same. Pre and postoperative fusion and stereopsis measurements are

summarized in table 2.

2


Table 2

Patient Preoperative fusion Postoperative fusion Stereopsis

Group 1 Near Distance Near Distance Preoperative Postoperative

D.K. -7¡/+12¡ -6¡/+12¡ -4¡/+4¡ -7¡/+12¡ 40 40

S.B. -7¡/+6¡ -4¡/+12¡ -4¡/+12¡ -3¡/+5¡ 80 100

V.B. -8¡/+15¡ -6¡/-+2¡ -4¡/+1¡ -6¡/+4¡ 40 50

V.M. -3¡/+20¡ -3¡/+20¡ -1¡/+1¡ -1¡/+4¡ 40 40

D.I. -2¡/+12¡ -2¡/+12¡ -3¡/+1¡ -3¡/+1¡ 400 400

S.C. -6¡/+7¡ -7¡/+8¡ -2¡/+4¡ -3¡/+4¡ 40 40

D.M. -4¡/+5¡ -3¡/+8¡ -2¡/+2¡ -2¡/+1¡ 40 40

W.M. -7¡/+9¡ -4¡/+5¡ -6¡/+4¡ -4¡/+6¡ 140 100

V.G. -2¡/+8¡ -2¡/9¡ -2¡/+5¡ -2¡/+3¡ 50 50

Group 2

M.C. -4¡/+8¡ -2¡/+20¡ -4¡/+6¡ -3¡/+3¡ 60 60

R.E. -4¡/+10¡ -4¡/+12¡ -2¡/+7¡ -3¡/+6¡ 40 40

D.R. -3¡/+8¡ -2¡/+2¡ -2¡/+3¡ -2¡/+3¡ 40 40

M.V. -8¡/+4¡ -4¡/+6¡ -2¡/+3¡ -3¡/+3¡ 40 40

N.A. -4¡/+8¡ -3¡/+8¡ -2¡/+4¡ -2¡/+4¡ 50 40

V.M. -6¡/+2¡ -3¡/+3¡ -3¡/+2¡ -3¡/+2¡ 40 50

D.J. -7¡/+12¡ -7¡/+12¡ -4¡/+4¡ -7¡/+12¡ 40 40

B.M. -4¡/+8¡ -4¡/+6¡ -2¡/+20¡ -3¡/+3¡ 40 40

Group 3

S.M. -2¡/+6¡ -3¡/+6¡ -2¡/+5¡ -1¡/+4¡ 40 40

V.F. -6¡/+20¡ -5¡/+17¡ -2¡/+12¡ -2¡/+12¡ 50 50

G.T. -5¡/+9¡ -4¡/+10¡ -3¡/+4¡ -3¡/+10¡ 60 50

Y.W. -4¡/+8¡ -3¡/+6¡ -2¡/+2¡ -3¡/+4¡ 40 40

Group 4

P.M -2¡/+3¡ -1¡/+10¡ -1¡/+10¡ -2¡/+3¡ 40 100

V.J. -6¡/+7¡ -5¡/+17¡ -3¡/+3¡ -4¡/+2¡ 40 50

K.C. -5¡/+3¡ -4¡/+5¡ -3¡/+3¡ -3¡/+2¡ 200 140

L.H. -6¡/+20¡ -7¡/+20¡ -2¡/+2¡ -3¡/+6¡ 40 40

In 8 eyes (5 patients) an improvement of the accommodation was seen, while in 15 eyes (9

patients) decrease of accommodation was found. In five of them the decrease was more than

3 diopters. In the majority (54%) accommodation did not change. The most remarkable

change we noticed in group 1. Pre and postoperative range of accommodation and

convergence is summarized table 3.

Table 3

Patient Preoperative accommodation Postoperative accommodation Convergence

Group 1 RE LE RE LE Preoperative Postoperative

D.K. 13 D 13 D 10 D 10 D Normal Normal

S.B. 9 D 9 D 12 D 9 D Normal Normal

V.B. 15 D 15 D 8 D 5 D Normal Normal

V.M. 3 D 3 D 5 D 5 D Normal Normal

D.I. 5 D 5 D 6 D 3 D Normal Normal

S.C. 20 D 20 D 9 D 7 D Normal Normal

D.M. 5 D 5 D 4 D 7 D Normal Normal

W.M. 12 D 12 D 7 D 9 D Normal Normal

V.G. 12 D 12 D 16 D 14 D Normal Normal

Mean values 10.44 D 10.44 D 8.55 D 7.66 D

Group 2

M.C. 8 D 8 D 10 D 10 D Normal Normal

R.E. 7 D 9 D 8 D 9 D Normal Normal

D.R. 8 D 8 D 7 D 8 D Normal Normal

M.V. 8 D 8 D 8 D 8 D Normal Normal

3


N.A. 3 D 4 D 4 D 4 D Normal Normal

V.M. 6 D 6 D 3 D 3 D Normal Normal

D.J. 3 D 3 D 3 D 3 D Normal Normal

B.M. 6 D 6 D 6 D 6 D Normal Normal

Mean values 6.13 D 6.5 D 6.13 D 6.40 D

Group 3

S.M. 10 D 10 D 9 D 10 D Normal Normal

V.F. 12 D 12 D 10 D 10 D Normal Normal

G.T. 9 D 10 D 10 D 10 D Normal Normal

Y.W. 10 D 12 D 8 D 12 D Normal Normal

Mean values 10.25 D 11.00 D 9.25 D 10.50 D

Group 4

P.M 10 D 8 D 8 D 8 D Normal Normal

V.J. 2 D 3 D 2 D 2 D Normal Normal

K.C. 2 D 2 D 2 D 2 D Normal Normal

L.H. 3 D 3 D 3 D 3 D Normal Normal

Mean values 4.25 D 4 D 3.75 D 3.75 D

Discussion

None of the patients presented changes in eye position, ocular motility, fusion, stereopsis and

convergence. In 30% of the patients accommodation decreased, in 16% it increased. In the

majority of patients, the ability to accommodate was unchanged.

The influence of frontwave aberrations differences pre and post LASEK could explain these

different reactions. This will be the subject of a further study.

References

1. Godts, D., Tassignon , M.J., Gobin, L. (2004). Binocular vision impairment after refractive surgery. J.

Cataract Refract. Surg. 30, 101-109.

2. Nemet, P., Levinger, S., Nemet, A., (2002). Refractive surgery for refractive errors which cause

strabismus. BinocularVision & Strabismus Quarterly. 17 (3): 187-190.

3. Kowal, L. (2000). Refractive surgery and diplopia. Clinical and experimental Ophthalmology 28, 344-

346.

4. Garner, L. F., Smith, G. (1997). Changes in equivalent and gradient refractive index of the crystalline

lens with accommodation. Optometry and Vision Science, 74(2), 114-119.

5. Koretz, J. F., Cook, C. A., Kaufman, P. L. (2002). Aging of the human lens: Changes in lens shape upon

accommodation and with accommodative loss. Journal of the Optical Society of America, 19(1), 144-

151.

6. He, J. C., Gwiazda, J., Thorn, F., Held, R., Huang, W. (2003b). Change in corneal shape and corneal

wave-front aberrations with accommodation. Journal of Vision, 3(7), 456-463.

4


Assessing The Dominant Eye: A New Method To Determine

Sensory Dominance During Binocular Vision

Claire Emmanouilidis, Elaine Cornell, Nathan Moss

The University of Sydney, School of Applied Vision Sciences

Sydney,

NSW, Australia

e.cornell@fhs.usyd.edu.au

Abstract

Introduction: Monovision correction by contact lenses or laser surgery involves correcting one

eye for distance vision and the other eye for near. The dominant eye is normally chosen for

distance correction and a form of sighting dominance is normally used to diagnose the

dominant eye. Previous research has shown that ocular dominance is task dependent, that is, it

may change depending on the visual task that is assessed. As monovision results in binocular

vision where each fovea is receiving images of different clarity a test that is based on retinal

rivalry (such as a sensory test) may be a better predictor of success following a monovision

procedure.

Methods: A novel test for sensory dominance was developed that could be readily used in a

clinical situation. Sighting and sensory ocular dominance were investigated in 46 subjects. A

two-tailed t test was performed to compare the laterality of ocular dominance between the two

tests.

Results: There was no significant relationship found between the two forms of ocular

dominance at either distance (p=0.124) or near (p=0.403), indicating that the response on one

test could not predict the response on the second test.

Conclusions: Responses of a sighting dominance test cannot predict the responses of s

sensory dominance test and thus the two forms of ocular dominance can be considered as two

separate entities.

Keywords

Ocular dominance, Monovision correction

Introduction

Lateralization in eye function is the result of the development of binocular vision, with the

overlapping of the visual fields of the two eyes 9 . The receptive fields in the two eyes are

identical for a given binocular cell of the cerebral visual cortex in terms of size, orientation,

motion sensitivity, and directionality. They are also are in precisely corresponding parts of the

contralateral visual field. However, the inputs from the two eyes are often not identical in

their relative influence on the cortical cell. Input from one eye is usually dominant and

produces a greater response to a given stimulus than the input from the other eye (1).

The complex underlying physiological mechanisms of eye function make it difficult to

provide a single definition that applies to all aspects of ocular dominance. Coren & Kaplan (2)

concluded that ocular dominance is a multifaceted phenomenon and their analysis revealed

three categories of ocular dominance (sighting, sensory, and acuity dominance) that were

categorised according to the visual task required and did not necessarily relate to the same

eye.

1


Sighting dominance relates to the eye that is preferred in monocular viewing such as

looking through an aperture. This form of dominance is the most commonly tested in clinical

investigations and many clinical phenomena are related to it. Sensory dominance is defined as

the eye that receives the input that is preferred when disparate sustained stimuli are presented

to the eyes in a binocular situation. It appears in situations where the system is trying to

suppress confusion or diplopia based upon conflicting inputs to the two eyes. Acuity

dominance is evident in situations when the vision in the two eyes is unequal for some

pathological or refractive reason or when strabismus exists; the eye with the better vision

attains the position of marked supremacy.

Current treatment of refractive error by contact lenses or laser surgery uses the

principle of monovision when one eye is corrected for distance vision and the other for near

vision. Cataract surgery also uses this principle that produces clear vision for distance and

near without glasses or the minimal use of glasses. Prior to these procedures the dominant

eye is determined, usually with a sighting test, and this eye is corrected for distance viewing.

However binocular in this post treatment period requires the person to deal with a clear image

on one fovea and a blurred image on the other, a situation that would be more realistically

assessed by a test that would assess sensory dominance.

The purpose of this study was to develop a simple clinical test based on sensory

dominance and to assess whether it could predict a person s response to a sighting test. In

other words, can a person have one eye that is dominant for a sighting test but the other eye

dominant for a sensory test?

Methods

Sighting and sensory ocular dominance were determined in 46 subjects, aged from 15-62

years of age who had visual acuity of at least 6/7.5 in each eye, anisometropia and/or

anisometropic astigmatism of no more than 1D and no manifest deviation in both near and

distance positions. To determine sighting dominance, the subjects were asked to create a

triangular aperture with their forefingers and thumbs and to hold this aperture at arm s length

whilst viewing the 6/60 letter of the distance (6m) vision chart. For near fixation (40cm)

aperture created was smaller and subjects placed the aperture halfway between the target (a

5mm diameter black circle on a white background) and their eyes. The sighting dominant eye

was recorded as the eye that was chosen by the subject to sight the target through the aperture

on three consecutive occasions.

As the purpose of the study was to provide clinically useful information in ocular

dominance, we designed a sensory dominance test that could easily be reproduced and used in

a clinical situation. The test was based on a retinal rivalry situation and incorporated the use

of polarized filters, in which the patient simultaneously viewed a pattern with one eye and a

similar, but inverted pattern with the other eye whilst wearing special polarized glasses. (See

Figure 1)

2


Figure 1. The Sensory Dominance Test.

Left: The test with the Polaroid glasses. Right (above) the image as seen by each eye

and (below) as seen binocularly without any retinal rivalry. Dark points are the points of

retinal confusion. See text for full details.

The test consisted of a 4.2cm x 4.2cm square with 4 polarized filter strips (6mm in

width and 42mm in length) placed horizontally and another 4 perpendicular polarized strips

bisecting the horizontal strips. The polarized strips were orientated so that when a subject

viewed the strips through the polarized glasses (with opposing polarization for each eye), two

horizontal and two vertical strips were seen with one eye and the other two horizontal and two

vertical strips were seen by the other eye (see Figure 1). The test was placed against a white

background at 40cm for near and at 4m for distance. Whilst wearing the polarized glasses, the

subjects were initially shown the pattern that each eye sees. They were then instructed to view

the pattern binocularly and to report aloud approximately every 5 seconds which pattern was

dominant over a period of 20-30 seconds. The eye that was seeing the pattern greater than

50% of the time over the time period in relation to the other eye was recorded as the sensory

dominant eye and expressed in terms of a percentage. If a subject saw the pattern an equal

amount of time with each eye this was defined as alternate dominance. The test was then

repeated at distance.

A 2-tailed t test was then performed to compare the laterality of sighting ocular

dominance with the percentage of right-eyed sensory ocular dominance.

Results

The mean right eye response in the sensory dominance test in subjects with right eye sighting

dominance was 52.7 ± 19.2 SD for near and 53.7 ± 34.7 SD for distance. The mean response

of right eye sensory dominance in subjects with left eye sighting dominance was 47.67 ± 18.8

SD for near and 36.95 ± 34.2 SD for distance. There was no significant relationship found

between the two forms of ocular dominance at either distance (p=0.124) or near (p=0.403).

That is, a person s sighting dominance could not predict their sensory dominance.

3


Near

Far

70

60

50

40

30

20

10

0

Right Left Alternating

70

60

50

40

30

20

10

0

Right Left Alternating

Sighting

Sensory

Sighting

Sensory

Figure 2: Responses (in %) of right eye, left eye or alternating dominance as assessed

by the Sighting Test (light grey) and the Sensory Test (dark grey) for far and near. Alternating

sensory dominance is particularly evident for near on the sensory test and there are a similar

number of right and left dominant responses for far on the sensory test.

Discussion

These findings confirm those of Coren and Kaplan (2) in that there was no relationship found

in laterality between the two forms of ocular dominance and thus each test can be categorised

relative to the visual task required. That is, sighting dominance is indicated by a number of

tasks which all require input from one eye either be excluded or ignored. Sensory dominance

appears in situations where the system is trying to suppress visual confusion based upon

conflicting inputs to the two eyes (2).

Further investigations are necessary to compare success of monovision correction

based on whether when the sensory or the sighting dominant eye is corrected for distance

fixation. However it is important to note that a high percentage of subjects had no eye

preference, particularly at near, according to the sensory test. These results were similar to the

results found by Robboy and Erickson (3) who used the anisometropic blur suppression test to

determine sensory ocular dominance. The smaller standard deviation of right eye response in

the sensory dominance test at near also demonstrates a weaker sensory dominance than at

distance where a larger standard deviation is present.

The responses of a sighting dominance test therefore cannot predict the responses of s

sensory dominance test and the two forms of ocular dominance can be considered to be two

separate entities. Sighting dominance is indicated by a number of tasks which all require

input from one eye either be excluded or ignored and sensory dominance occurs in situations

where the system is trying to suppress visual confusion based upon conflicting inputs to the

two eyes.

References

1. Pearlman, A. (1897) The central visual pathways. in Moses RA, & Hart WM (Ed), Adler s Physiology of the

Eye: Clinical Application. (pp583-618). St Louis: Mosby,

2. Coren, S., Kaplan, C. (1973) Patterns of ocular dominance. J Optom Arch Am Acad Optom 50, 283-292

3. Robboy, M., Cox, I., Erickson, P. (1990) Effects of sighting and sensory dominance on monovision high and

low contrast visual acuity. CLAO J 16(4), 299-301

4


Does Dissociation Reduce Stereoacuity?

Helen Davis a , Michelle Tewkesbury a , Jonathan Dominic a , John P Frisby b ,

David Buckley a

a Academic Unit of Ophthalmology & Orthoptics University of Sheffield S10 2JF b Dept. of

Psychology University of Sheffield, S.Yorkshire, S10 2TN, UK. Email:

h.davis@sheffield.ac.uk

Abstract

Purpose: To ascertain if reduction in stereoacuity is caused by dissociation, defined as optical

disruption of the equality of the visual stimulus to each eye.

Methods: Experiment 1: 18 normal observers were tested using the Frisby Near Stereotest

(FNS) in free-space and then in random order, the FNS seen through Bagolini glasses,

Polaroid glasses and red & green glasses. Experiment 2: 29 normal observers were first

tested for near with the FNS and for distance with the Frisby Davis Distance Stereotest (FD2)

in free-space and then looking through Bagolini glasses with the striations at 180° to each

other and perpendicular to each other. Re-testing with viewing through red/red, red/green &

green/green goggles followed this.

Results: Experiment 1: There was a significant (p


some discussion as to whether dissociation has a role in the results of stereoacuity testing. A

recent report suggests that prior dissociative testing of a patient does not necessarily have an

adverse effect on their sensory testing results (5). Even so, the possibility of dissociation

affecting stereoacuity results is important. For example, evidence has been reported that the

level of distance stereoacuity may relate to the control of intermittent exotropias (6) and may

therefore be useful in determining the optimum time for surgery. However, this finding was

not replicated in a study using the free space non-dissociating FD2 distance stereoacuity test,

which found that when distance stereopsis was achieved at all in these patients it was as good

as in normal controls (7).

The present study set out to investigate the role of dissociation further and to compare

dissociative optical disruption to visual disruption that is the same for both eyes. Experiment

1 concentrated on the dissociation aspect whilst Experiment 2 looked at equal visual

disruption in addition to dissociation.

2


Methods

Observers were students in the University of Sheffield. Inclusion criteria were: visual acuity

of 6/6 or better in each eye, no significant heterophoria, and 40" of arc or better stereoacuity

tested using the FNS. Both experiments were repeated measures designs.

In Experiment 1 observers (n=18) were first tested using the FNS presented in free

space and tested to threshold and then viewed through three different forms of dissociation in

random order: standard Bagolini glasses, Polaroid glasses used with the Randot Stereotest and

red/green glasses.

In Experiment 2 observers (n=29) were first tested with the FNS and then the FD2,

(fig.1) and the initial threshold stereoacuity recorded. These tests were then repeated under

the following viewing conditions: Bagolini glasses with striations parallel giving the same

image to each eye, Bagolini glasses with left/right eye striations perpendicular to each other;

red/red goggles, red/green goggles and green/green goggles. All near testing was completed

prior to distance testing.

Results

Experiment 1: Paired t tests revealed that the difference between normal free space FNS

stereoacuity and with Bagolini glasses was not significant, however, with both Polaroid and

red and green glasses the difference from normal was significant (p


n.s. **

Polaroid 0.9

n.s.

**


Initial 1.2

**

1.4

**

6.4

****

7.1

****

9.8

****

2.6

****

3.8

****

10.5

****

9.6

****

Parallel

0.2

1.2

(Para)

n.s.

*

Perpendicular

(Perp)

Red/Red

0.7 3.4

1.0

(RR)

n.s. *

n.s.

Green/Green

2.7

(GG)

n.s.

Red/Green

(RG)

*


References

1. Schmidt, PP. (1994). Sensitivity of random dot stereocuity and Snellen acuity to optical blur. Optometry

and Vision Science, 71 (7), 466-471.

2. Donzis, PB., Rappazzo, JA., Burde, RM., Gorden, M. (1983). Effect of binocular variations of Snellen's

acuity on Titmus stereoacuity. Archives of Ophthalmology, 101, 930 – 932.

3. Lovasik, JV., Szymkiw, M. (1985). Effects of aniseikonia, anisometropia, accommodation, retinal

illuminance, and pupil size on stereopsis. Investigative Ophthalmology & Visual Science, 26(5), 741-50.

4. Tutte, K., Whittle, J., Davis H. (1988). The effect of red/green filters on TNO stereoacuity. British

Orthoptic Journal, 45, 26-29.

5. Jenkins, PF., (2002). The effect of dissociation on the sensory status. American Orthoptic Journal, 52, 85-

88

6. Stathacopoulos, RA., Rosenbaum, AL., Zanoni, D., Stager, DR., McCall, LC., Ziffer, AJ., Everett, M.,

(1993). Distance stereoacuity. Assessing control in intermittent exotropia. Ophthalmology,. 100(4), 495-

500.

7. Haggerty, H., Richardson, S., Hrisos, S., Frisby, JP., Davis, H., Clarke, MP. (2004). Distance stereopsis in

intermittent distance exotropia: now you see it, now you don’t! Poster presented at 30th Meeting of

AAPOS, Washington, USA.

6


Does stereoacuity correlate with interpupillary distance

for normal observers?

John P. Frisby a , Emma Patchick a , Rebekah Edgar a , and Helen Davis b

a Department of Psychology University of Sheffield Sheffield S10 2TNUK

b Academic Unit of Ophthalmology & Orthoptics University of Sheffield, S.Yorkshire S10 2JF UK

e-mail: j.p.frisby@sheffield.ac.uk

Paper:

Abstract Interpupillary distance (PD) contributes to the size of binocular disparities yet it is

not known whether individual differences in stereoacuity correlate with PD. We measured

stereoacuities of 186 university students with normal vision. Stereoacuities were measured

using the Howard-Dolman task which requires setting two adjacent vertical rods to apparent

equidistance. One group (n=109) made distance settings (either at 5.5m or 4.9m), a second

group (n=77) made near settings (1m). PD was measured using a PD meter set for either

distance or near viewing as appropriate. Stereoacuities were normalised to group means to

eliminate mean differences between near and distance stereoacuities and then log transformed

to overcome skew. The resulting relative stereoacuities correlated significantly with relative

PD (r = -0.24, p


of 146″ and 114″ (sec arc) for PDs of 70 and 55mm respectively. These values are

approximations and assume targets viewed in central vision with symmetrical gaze. The

contrast between distance and near reflects the fact that disparities are scaled inversely with

the square of the fixation distance. Given these values and that many other factors affect

stereoacuity, this study used a large sample size of observers for the required statistical power.

Methods

Stereoacuities were measured using the Howard-Dolman task which requires setting two

adjacent vertical rods to apparent equidistance. The two rods were black and seen against a

brightly lit white background through a window in a white screen set about 20cm in front of

the fixed rod. The screen obscured the supports for the rods. The participant adjusted the

position in depth of one rod using either a long thin smooth hand-held pole (distance settings)

or by rotating a knob that that operated a ratchet linkage to the moveable rod (near settings).

In both cases, the participant could not make settings using unwanted cues from seeing the

pole or the ratchet mechanism as these were obscured by black cloth. Head movement

parallax cues were controlled with a chin rest. Pilot trials established that accuracy in rod

settings deteriorated dramatically under monocular viewing, demonstrating that the task was

performed using binocular cues.

Various apparatus constraints meant that the visual angles subtended by rod width, rod

separation and window size were different for the distant and near tasks. Thus, for the

distance and near cases respectively, rod widths were approximately 10’ and 7’ (min arc), rod

separations were 7.7º and 0.8º, and the width/height window sizes were 11.7º/4º and 2.5º/1º.

Allowance was made for these differences in the analysis by normalising the data to group

means. Each participant made 10 equidistance settings successively. They were encouraged to

complete each one in fewer than 10 secs. There was a pause between settings during which

the screen window was masked and the moveable rod set a few cm in front of or behind the

fixed rod. Practice was limited to the minimum needed for the observer to understand the

task. No feedback was given until all 10 settings were completed. The measure of stereoacuity

was 0.6745 of the standard deviation (SD) of the 10 settings to equidistance. This gives an

estimate of the semi-interquartile range of the psychometric function, which is a standard

measure of a difference threshold.

The participants were 186 psychology students of the University of Sheffield

attending laboratory classes. They gave their informed consent. Inclusion criteria were: no

strabismus or amblyopia history, 2.5SDs from the group

means, suggesting that they were unable to do the task on the same basis as other

participants). There were two groups of students run in successive years. One group (n=109,

mean age 19.9 yrs, range 18-22 yrs) made distance settings with the fixed rod set at 5.5m or

4.9m according to available room size. The second group (n=77, mean age 18.7 yrs, range 17

-24 yrs) made near settings with the fixed rod set at 1m. PD was measured using a PD-82II

Digital PD Meter (Towa Medical Instruments Co. Ltd) set for either distance or near viewing

as appropriate. PDs were first measured a few weeks prior to the stereoacuity measurements

in order to ensure that students from the ends of the PD range of the whole class (n > 300)

were invited to be participants, as time did not permit including all of them in the study. This

selection criterion did not lead to prominent bimodality in PDs as there were few students at

the ends of the PD distribution. PDs were measured again on the days when stereoacuities

were measured for confirmation, yielding the PD values used in the analyses.

2


Results

The distance and near stereoacuities produced similar correlations with PD when analysed

separately. Space limitations forbid a full report of each group’s data here (data from the

distance group have been reported elsewhere; ref. 3). Instead, we concentrate on a combined

analysis, in which each participant’s results were normalised to their group means, yielding

relative measures as the data for Pearson product moment correlations. Using relative

measures eliminated the variation in PD measurements arising from using distance and near

settings on the PD meter. It also eliminated differences in group means for the distance and

near stereoacuities. The group means prior to normalisation were: distance PD 60.3mm (SD

3.8mm); near PD 56.5mm (2.7mm), distance stereoacuity 5.3″ (2.4″), near stereoacuity 34″

(14″). We interpret the latter difference as caused by differences in the details of the two

Howard-Dolman displays rather than a genuine difference in near and distance stereoacuities.

For example, apparatus factors related to the ratchet mechanism meant that the rods had to be

separated by about 7.7º in the near case, as against only 0.8º for the distance settings. This

wider separation is likely to have made the near task harder.

Fig. 1 Frequency distribution of relative PD (N=186).

Fig. 2. Frequency distribution of relative

stereoacuities ( N=186)

Figs. 1 and 2 show frequency distributions of the relative PDs and relative

stereoacuities (equivalently, stereo thresholds). The stereoacuities were not normally

distributed, showing a longer tail for the larger values as is typical in this kind of data. This

skew was removed for correlations using a log transformation. Fig. 3 shows a scattergram of

the correlation (r = -0.24, p


small percentage (a few sec arc) of the observed stereoacuity variation. We conclude that it is

of theoretical interest rather than of clinical importance. It needs to be borne in mind,

Fig. 3. Scattergram of log relative stereoacuity against relative PD, with regression line (N=186).

Fig. 4. Scattergrams of log relative stereoacuity against relative PD for females (N=119) and males (N=67),

with regression lines.

however, that our near viewing distance was 1m. The risk of monocular cues affecting

Howard-Dolman task measurements for near distances precluded us testing at the customary

near clinical test distance of 40cm. It is also noteworthy that distance stereoacuities measured

with the FD2 (4), which was administered to the distance group (3), did not show a significant

correlation with distance PD. The FD2 is designed for clinical use and its procedures meet

clinical needs for a fairly speedy assessment of distance stereoacuity, thus producing less

precise measures than the more protracted laboratory-based Howard-Dolman task used here.

Acknowledgements

Michael Port and Andy Ham for apparatus construction. Robin Farr for help with figures.

References

1. Lang, J., Rechichi, C., Stürmer, J. (1991). Natural versus haploscopic stereopsis. Graefe’s Arch Clin Exp

Ophthalmology, 229, 115-118.

2. Gockeln, R. (1996). Der Einflub der Interpupillardistanz auf die Tiefensehschärfe. Klinische Monatsblatter

fur Augenheilkunde, 209(4), 205-210.

4


3. Frisby, J.P., Davis, H., Edgar, R. (2003). Does interpupillary distance predict stereoacuity for normal

observers? Perception, 32 (Supplement), 73-74.

4. Frisby J.P., Davis H. (2003). Clinical tests of distance stereopsis: state of the art. Transactions of the 9th

International Strabismological Association, Sydney, 187-90.

5


Assessment Of Sensory Ocular Dominance

Junko Fujita a , Takahiro Niida a , Kazuo Mukuno b

a Department of Orthoptics and Visual Science, School of Health Science,

International University of Health and Welfare

2600-1 Kitakanemaru, Otawara, 324-8501 JAPAN

b Kanagawa Dental College, Yokohama Dental & Medical Clinic

3-31-6 Tsuruya-cyo, Kanagawa-ku, Yokohama, 221-0835 JAPAN

jfujita@iuhw.ac.jp

Abstract

Purpose: To evaluate the nature of sensory ocular dominance, durations of the exclusive

perceptual dominance and modulation of the visual evoked potential (VEP) during binocular

rivalry were studied.

Methods: Nineteen healthy volunteers, aged 21 - 29, were participated. All had corrected-tonormal

visual acuity and normal stereo acuity. To measure durations of the exclusive

perceptual dominance, static black-and-white orthogonal bars were presented dichoptically.

Stimulus areas were 2, 2 - 5, 5 - 8 degree and their bar widths were 10, 15, 20 min arc,

respectively. Subjects were instructed to press either of two buttons to report which stimulus

was perceptually dominant. The modulation of transient VEP was calculated as the change

(%) of the amplitude during rivalry (two diagonal bars oriented orthogonally) to the amplitude

during fusion (those oriented similarly).

Results: Most of subjects showed the longest exclusive dominance at 2 degree stimulus.

Modulation of VEP ranged from – 39 to + 53 % and was categorized into three groups;

negative (< – 10 %), constant (≤ ± 10 %) and positive (> + 10 %). Relatively shorter durations

of perceptual dominance were seen in weak modulation group. Negative modulation group

showed a longer perceptual dominance even in 5 - 8 degree stimulus as well as a significantly

larger exophoria than positive modulation group.

Conclusion: It seems that positive modulation reflects a heightened visual attention by robust

rivalry and constant modulation reflects a piecemeal rivalry with weak sensory dominance. In

contrast, alternately extensive suppression of either eye as well as sub-optimal viewing

condition by ocular positions is responsible for negative modulation. These combined

methods should be useful to assess the strength of sensory ocular dominance.

Keywords

Sensory ocular dominance, Binocular rivalry, Exclusive perceptual dominance, Visual evoked

potential (VEP)

Introduction

An ocular dominance is roughly divided into three factors (1), i.e., Sighting, Sensory, Acuity

dominance. Magnitude of sensory ocular dominance is used as one of the indicator when we

choose therapy of anisometropic amblyopia and predict success of the monovision which is a

method to compensate for presbyopia. Binocular rivalry is usually used for an evaluation of

Sensory dominance. Binocular rivalry is a phenomenon in which dissimilar monocular

patterns presented to corresponding regions of the two eyes compete for perceptual

dominance, producing alternations in the visibility of one pattern. The dominant eye is

defined as the one that maintains its view in consciousness for a longer period of time (1).

Recently our colleagues have developed “balancing technique” (2) for quantitative

1


measurement of sensory dominance (3, 4), however, physiological assessment of sensory

dominance has not yet been fully established. In this study, in order to elucidate the nature of

sensory dominance, a correlation between the durations of the exclusive perceptual

dominance and the modulation of the visual evoked potential (VEP) during binocular rivalry

was investigated.

Material and Methods

Nineteen subjects (3 males and 16 females) without an ophthalmologic disorder participated

with this experiment. The ages of subjects were 21 - 29 years old (an average of 24.6 ± 2.46

years old). All had corrected - to - normal visual acuity and normal stereo acuity of at least 60

sec of arc and no distinct heterotropia. To measure durations of the exclusive perceptual

dominance, static black - and - white orthogonal bars were presented dichoptically with a

major amblyoscope (type 2001, Clerment Clarke). Stimulus areas were 2, 2 - 5, 5 - 8 degree

and their bar widths were 10, 15, 20 min of arc, respectively. Subjects were asked to fixate on

the red dot in center of each stimulus, and they were instructed to press either of two buttons

to report which stimulus was perceptually dominant. One trial was measured for 60 seconds

and sum of 3 trials was used for analysis. Perceptually dominant times of each subject were

divided into Right, Left, Both. “Right” is the total time when the image of right eye was

perceived. “Left” is the total time when the image of left eye was perceived. “Both” is the

total time when the images of right and left eyes were perceived simultaneously (piecemeal

rivalry). Transient VEP was recorded with Neuropack 8 (Nihon Kohden). In VEP recording,

bipolar configuration was chosen, the active electrode was 2.5 cm above the inion, the

reference was 12cm above the nasion and the ground was on the earlobe. Stimulus conditions

were as follows: mean luminance of 30 cd/mm 2 , 87 % contrast, field size of 11 degree, bar

widths of 15 min of arc, at a frequency of 2 rev/sec, and One hundred sweeps were averaged.

A small LED spot in the center of the display served as a fixation guide. The modulation of

transient VEP was calculated as the change (%) of the amplitude (N1P1) during rivalry (two

diagonal bars oriented orthogonally) to the amplitude (N1P1) during fusion (those oriented

similarly). The change of the amplitude was derived by using the following formula : [(rivalry

amplitude – fusion amplitude) / fusion amplitude]× 100. Objective angle of ocular deviation

was measured with a major amblyoscope.

Results

Most of subjects (17/19) showed the longest exclusive dominance at 2 degree stimulus (Fig.1).

Modulation of VEP ranged from – 39 to +53 % and was categorized into three groups:

negative (< –10 %), constant (≤ ±10 %), and positive (> +10 %) (Fig.2). Seven subjects were

negative, 8 subjects were constant, and 4 subjects were positive. Relatively longer durations

of perceptual dominance were seen in negative and positive modulation group. Negative

modulation group showed a longer perceptual dominance even in 5 - 8 degree stimulus than

positive and constant modulation group. Furthermore, average ocular deviations of a negative

modulation group showed significantly larger exophoria than those of the positive modulation

group (multiple comparison test, Tukey kremer, p < 0.05).

Discussion

It is generally accepted that the durations of exclusive perceptual dominance in binocular

rivalry reflects the strength of sensory dominance (1, 2, 5, 6). In this study, different bar width

corresponding to the retinal resolution of each stimulus area was used. Nevertheless, for most

subjects, the longest exclusive dominance was seen at 2 degree stimulus. This result is

consistence with previous report (6). Recent fMRI study during binocular rivalry revealed that

alternation of perceptual dominance coincides well with the activity of visual cortex and V1

2


activity in suppression phases is apparently reduced (7). Although averaged VEP we

employed could not detect such a real-time modulation, it has been shown that averaged

binocular VEP amplitude in rivalry condition is larger than those in fusion condition (see

Brown and Norcia, 1997 for details). It is well known that VEP amplitude is affected by a

number of factors such as visual attention, adaptation and stimulus conditions (9). Lee et al.

(7) have reported that a heightened visual attention is required in binocular rivalry. Taking

these into consideration, it seems that positive modulation reflects a heightened visual

attention by robust rivalry and constant modulation reflects a piecemeal rivalry with weak

sensory dominance. On the other hand, it has been reported that monocular suppression in

strabismic patients or artificially induced diplopia results in the inhibition of binocular VEP

responses (10). Therefore, a longer perceptual dominance even in 5-8 degree stimulus as well

as negative modulation of VEP amplitude presumably reflects alternately extensive

suppression of either right or left eye, rather than binocular rivalry. In addition, sub-optimal

viewing condition by fluctuation of ocular positions seems to be responsible for negative

modulation, since this group has a significantly larger exophoria as compared with the

positive modulation group. In summary, it is considered that these combined methods should

be useful to assess the strength of sensory ocular dominance.

Acknowledgements

This study was supported by Grants in Aid for Scientific Research (J. Fujita; No.16791064, T.

Niida; No.14571686) of Japan Society for the Promotion of Science.

References

1. Porac, C., Coren, S. (1976). The dominant eye. Psychological Bulletin, 83(5), 880-897.

2. Ooi, T. L., Optom, B., He, Z. J. (2001). Sensory eye dominance. Optometry, 72(3), 168-177.

3. Handa, T., Mukuno, K., Uozato, H., Niida, T., Shoji, N., Minei, R., Nitta, M., Shimizu, K. (2004). Ocular

dominance and patient satisfaction after monovision induced by intraocular lens implantation. J Cataract

Refract Surg, 30(4), 769-774.

4. Handa, T., Mukuno, K., Uozato, H., Niida, T., Shoji, N., Shimizu, K. (2004). Effects of dominant and

nondominant eyes in binocular rivalry. Optom Vis Sci, 81(5), 377-383.

5. Weinman, J., Cooke, V. (1982). Eye dominance and stereopsis. Perception, 11, 207-210.

6. Blake, R. (1989). A neural theory of binocular rivalry. Psychological Review, 96, 145-167.

7. Lee, S. H., Blake, R. (2002). V1 activity is reduced during binocular rivalry. Journal of Vision, 2, 618-626.

8. Brown, R. J., Norcia, A.M. (1997). A method for investigating binocular rivalry in real-time with the steadystate

VEP. Vision Res, 37(170), 2401-2408.

9. Shandiz, J. H., Douthwaite, W.A., Jenkins, T. C. A. (1992). Effect of attention on the VEP in binocular and

monocular conditions. Ophthal. Physiol. Opt., 12, 473-442.

10. Campos, E. C. (1980). Anomalous retinal correspondence. Monocular and binocular visual evoked responses.

Arch Ophthalmol, 98, 299-302.

3


Fig. 1. Durations of exclusive perceptual dominance.

Fig. 2. Total durations of the exclusive perceptual dominance (right + left) and the modulation of VEP amplitude

(negative < –10%, constant ≤ ±10%, positive > +10%). The mean heterophoria angle was significantly different

between positive group and negative group.

4


The Age-Related Decline in Stereopsis as Measured by Different

Stereotests

Louise Garnham and John Sloper

Moorfields Eye Hospital

City Road

London, UK

louise.garnham@moorfields.nhs.uk

Abstract

Stereoacuity has been reported to decline with age (For review see Zaroff et al 1 ). The present

study has examined whether a reduction in stereoacuity is found using a range of stereo tests.

Sixty subjects, aged 17-83 years had their stereoacuity assessed using the TNO, Titmus and

Frisby-Davis distance tests. All had good vision in each eye and no history of ophthalmic

disease. Motor fusion was also assessed. Stereoacuity as measured by all stereotests declined

with age with a marked drop in 5 subjects over 55 years with the TNO test. Much better

stereoacuity was found in these 5 cases with the other stereo tests. Results of random-dot

stereotests should be interpreted with caution in older patients.

Keywords

Stereoacuity; TNO, Titmus, Frisby and Frisby-Davis stereotests

Introduction

Stereoacuity declines with age, with a “catastrophic drop” having been described in some

elderly subjects using a random-dot stereotest 1 . Because stereoacuity depends on cortical

disparity detecting neurons, the decline in stereoacuity has also been interpreted as showing

declining cortical function. The present study has examined whether a similar drop in

stereoacuity is found in using a range of stereo tests, which utilize different types of stimulus.

Material and Methods

Stereoacuity has been measured in 60 normal subjects aged 17-83 years by the same observer

using TNO, Titmus, Frisby near and Frisby-Davis distance stereotests. All subjects had a best

corrected Snellen acuity of 6/9 in each eye and had no history of ophthalmic disease. An

orthoptic examination was carried out including assessing motor fusion for near and distance

using prisms.

Results

For all tests stereoacuity declined with age, (P


The results of all four stereotests confirmed that there is some decline of stereoacuity with age

for both near and distance. It seems likely that this reflects a decline in the function of cortical

disparity detectors with age. However some older patients showed a much greater reduction in

stereoacuity as measured by the TNO test.

These five patients with very poor TNO but good stereoacuity with the Titmus test are of

particular interest. Care was taken to ensure that they were not utilizing monocular clues with

the Titmus test by ensuring that they were seeing the stimulus circle stand out from the page

and not simply as different and that inversion of the page made the circle appear behind its

surround. These patients have good cortical disparity detectors as they have good stereo to a

contoured stimulus. The most likely explanation for their poor TNO stereoacuity was that

their fusion reflex was not able fully to overcome the dissociative effect of the TNO test. In

the real world most judgements of depth are performed utilising the disparity of contours,

which is more like the stimuli utilised by the Titmus test.

The large drop in stereoacuity seen in some older subjects using the random dot tests is

probably due to the dissociative effect of the test on fusion rather than a loss of cortical

disparity detectors. Results of random-dot stereo tests should be interpreted with caution in

older patients.

References

1. Zaroff, C.M., Knutelska, M. and Frumkes,T.E. 2003. Variation in stereoacuity: normative

description, fixation disparity, and the roles of aging and gender. Invest Ophthalmol Vis Sci:

44: 891-900.

2


A Clinical Quantitative Measurement Of Ocular Dominance

Tomoya Handa a , Hiroshi Uozato a , Kazuo Mukuno a , Takahiro Niida b

Nobuyuki Shoji a , Risako Higa c , Marie Nitta c , Kimiya Shimizu c

a Department of Orthoptics and Visual Science, School Allied Health Sciences, Kitasato

University,

1-15-1 Kitasato, Sagamihara, Kanagawa, 228-8555 Japan.

b Department of Orthoptics and Visual Science, School of Health Science, International

University of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara ,Tochigi,

324-8501 Japan

c Department of Ophthalmology, School of Medicine, Kitasato University,

1-15-1 Kitasato, Sagamihara, Kanagawa, 228-8555 Japan.

thanda@kitasato-u.ac.jp

Abstract

Clinical usefulness of a quantitative measurement of ocular dominance was investigated in

normal subjects and in monovision patients. The magnitude of ocular dominance was

measured using our balance technique based on binocular rivalry. In the magnitude of ocular

dominance, normal subjects showed the large individual variation and unsuccessful

monovision patients were significantly higher than successful monovision patients. Our

balance technique showed the large individual variation seen in the magnitude of ocular

dominance and success and the great influence in success and patient satisfaction in

monovision.

Keywords

Ocular dominance, Binocular rivalry, Sensory eye dominance, Balance technique,

Monovision

Introduction

Clinically, ocular dominance which is judged by a hole-in-card test is the most facile

investigative tool for sighting ocular dominance. However, this test is unable to quantitatively

assess the magnitude of ocular dominance. Therefore, most clinicians are unable to evaluate

the effects of ocular dominance in visual function, especially, evaluating patients having

bilateral cataract surgery who opt for monovision. Monovision is an optical means of

correcting presbyopia, where dominant eye is corrected for distance and nondominant eye for

near.

Recently, we developed a balance technique to quantitatively evaluate the quality of

ocular dominance. 1, 2 In present study, a clinical usefulness of our balance technique based on

binocular rivalry was investigated in normal subjects and monovision patients.

Material and Methods

The quantity of ocular dominance (sensory dominance) measured in 20 normal subjects, and

16 successful and 4 unsuccessful monovision patients induced by implanted intraocular lenses,

using our balance technique 1, 2 (see below for details) based on binocular rivalry. The

dominant eye was determined using the hole-in-card test (sighting dominance).

Our balance technique 1, 2 : subjects and patients were presented with binocular rivalry

targets, i.e., rightward tilted (45º) and leftward tilted (135º) shaped patches of rectangular 2

c/deg gratings that were 4 deg in size. The contrast of the target in the dominant eye was

1


varied, from 100% to 80% to 60% to 40% to 20%, while that in the nondominant eye was

fixed at 100% in all trials. Subjects estimated the exclusive visibility as a general dominance

of trial target visibility when compared with that of another targets. For the dominant eye

trials, subjects were told to press the button when the dominant eye target was exclusively

visibility during the dominant eye target was varied from 100% to 80% to 60% to 40% to

20%. For the nondominant eye trials, patients were told to press the button when the

nondominant eye target was exclusively visibility during the nondominant eye target was

fixed at 100%. Each trial lasted 1 min and was followed by an inter-trial interval of 1 min. All

trials were repeated 2 times. The qualities of ocular dominance were quantitatively evaluated

as reversal point where exclusive visibility of the nondominant eye crosses over that of the

dominant eye.

Weak ocular dominance is defined as the reversal points (where exclusive visibility of

the nondominant eye crosses over that of the dominant eye) were obtained in low decreasing

contrast of 80% and 60% in the dominant eye target. In contrast, strong ocular dominance is

defined as the reversal points were observed at high decreasing contrast of 40% and 20% or

not at all in the dominant eye.

Results

The sighting dominant eye identified by hole-in-card test coincided the sensory dominant eye

as determined by binocular rivalry. All subjects and patients recognized binocular rivalry

regardless of varying contrast in dominant eye. Fig.1 show the reversal point (exclusive

visibility of the nondominant eye crosses over that of the dominant eye) in normal subject and

monovision patients. The 15 normal subjects showed reversal point at 80% and 60%; the

other 5 subjects showed reversal point at 40% and 20%. Reversal point 80% and 60% are

weak magnitude comparison with 40% and 20%. In monovision patients, the reversal points

(20% and not at all) in unsuccessful patients were a significant lower contrast than that (80%

and 60%) in successful patients (p


Discussion

An important clinical finding shown by the current study was large individual variation seen

in the magnitude of ocular dominance, and success and patients satisfaction in monovision are

greatly influenced by the magnitude of ocular dominance. Our balance technique seems to be

a useful clinical quantitative measurement of ocular dominance. Further studies are needed to

clarify the role of ocular dominance in binocular vision.

Acknowledgements

This study was supported in part by Grant from the Ministry of Education, Science, Sports,

Culture, and Technology, Japan (No.14571686)

References

1. Handa, T., Mukuno, K., Uozato, H., Niida, T., Shoji, N., Minei, R., Nitta, M., Shimizu, K. (2004) Ocular

dominance and patient satisfaction after monovision by implanted intraocular lenses. J Cataract Refract

Surg, 30:769-774.

2. Handa, T., Mukuno, K., Uozato, H., Niida, T., Shoji, N., Shimizu, K. Effects of dominant and nondominant

eyes in binocular rivalry. (2004) Optom Vis Sci, 81:377-382.

3


Can stereo tests be an indicator of decreased visual acuity?

Toshie Hirai, Keisuke Takahashi, Yoshikatsu Kawase,

Muneko Tanabe and Norio Ohba

Orthoptics and Vision Science, Faculty of Medical Welfare, Aichi Shukutoku University,

23 Sakuragaoka Chigusaku Nagoya, Japan, 464-8671

e-mail: hiraito@asu.aasa.ac.jp

Abstract

Purpose: To study the correlation between visual acuity(VA) and stereoacuity and to assess

the value at which a person can maintain or lose stereopsis.

Subjects and Method: Thirty normal subjects (aged 18 to 22, mean 20 years old) were

examined with the Titmus stereo test (the Titmus) and the Lang stereotest I (the Lang). VA of

the non -dominant eye of each subject was lowered stepwise by a set of seven different filters

originated by N Bangerter. VA was measured with the log MAR chart (expressed decimal)

and the VA and stereo tests were examined at a distance of 40 cm.

Results: Ninety-seven percent of the subjects with VA of 0.32 in their non-dominant eye

passed the Lang and 100% of subjects whose decreased VA was 0.4 passed the animal

test in the Titmus. In the results of the circle test of the Titmus, subjects with VA

of 0.32 ranged from 0/9 (1/9: 800 seconds of arc (") to 9/9 (40") and 64% of subjects with

VA of 0.62 obtained the best score of 9/9 (40"). Eighty-three percent of subjects with VA of

0.125 failed all tests.

Conclusion: VA and stereoacuity is correlative, yet there is much discrepancy among

subjects. Therefore, stereoacuity cannot be an accurate indicator of VA, it gives rise to a gross

estimation. To establish stereoscopic vision, VA of 0.3 and above is required.

Keywords

Visual acuity, stereoacuity, Titmus stereo tests, Lang stereotest.

Introduction

It is generally accepted that there is a linear relationship between stereoacuity and visual

acuity (VA)(1). Thus, stereo tests are used for vision screening of preschool children (2, 3, 4)

and adults(5) along with a device to assess possible malingering(6). However it is reported

that the Lang fails to screen 60 to 70% of children with amblyopia. On the contrary, Brown et

al. (5) who examined 292 (adults aged 44-90, mean 59.4 years old) using the Lang found that

19 (6.5%) participants failed the test and failure was associated significantly (p


Subjects and Methods

Thirty normal subjects (male: 6, female: 24, aged 18 to 22, mean 20 years old) were examined

with the Titmus and the Lang. VA of the 30 normal subjects was1.0 or better in each eye and

all passed the circle test in the Titmus (9/9: 40"). VA of the non-dominant eye of each subject

was reduced stepwise using a set of seven different filters originated from N.Bangerter

(Transparent Occlusion, Ryser Optic, ST.Gallen, Switzerland). VA was measured with the

near log MAR chart (Nitten, Nagoya, Japan) originated by H.Uosato and O.Katsumi (Fig 1).

VA was divided into 12 levels from 1.0(0) to 0.08(1.1). Stereo tests were also examined at a

distance of 40 cm at each new level of monocularly degraded VA. The tests were

discontinued after 1) VA reached the point where no stereo test was possible or 2) the Titmus

stereo test score reached 9/9 for stereo acuity.

Fig.1 log MAR Visual Acuity Chart for Near (Landolt ring)

Results

The seven filters, which we used, reduced the normal vision to less than 0.1(< 0.1 ),0.1, 0.2,

0.3, 0.4, 0.6, 0.8. However, the filter of < 0.1 was so effective at lowering the VA of subjects,

that no one could distinguish any marks in the chart. Therefore, we did not use the filter. On

the contrary, no subject obtained VA of 0.1 using only one filter of 0.1 and none of the

filters offered the VA that they specified. Many subjects needed to wear two 0.1 filters and

one 0.3 filter above their non-dominant eye to lower their VA to 0.1. Thus, filters did not

work as we thought they would. In addition we discontinued the tests when we obtained pass

scores in the 3 tests. Therefore, the subjects who were divided into 12 different levels of VA

stages were in total not 180 subjects ( 6 filters x 30 subjects ), but 126. Therefore,

approximately one subject participated 4 times in these experiments, even though the number

of stepwise filters was 7. Each result is shown in Table 2, 3, 4.

2


Pass

No.

Table 1. Number .of subjects

with decreased VA

No. of

Decimal Log M

subject

1 0.08 1.1 6

2 0.1 1.0 18

3 0.125 0.9 5

4 0.15 0.8 16

5 0.2 0.7 9

6 0.25 0.6 10

7 0.3 0.5 15

8 0.4 0.4 12

9 0.5 0.3 12

10 0.64 0.2 14

11 0.8 0.1 8

Table 2.The results of the Lang

12 1 0 1

0/3 1/3 2/3 3/3126

Total

1.0 0 0 0 1 1

0.8 0 0 0 8 8

0.64 0 0 0 14 14

0.5 0 0 0 12 12

0.4 0 1 0 11 12

0.3 1 0 0 14 15

0.25 2 0 2 6 10

Pass

Fail

0.2 2 0 2 5 9 Fail

0.15 6 1 4 5 16 Ninety-seven percent of the subjects with VA of

0.125 4 1 0 0 5 0.32 in their non-dominant eye passed the Lang

(normal value: 3/3:Cat:1200" Star: 600", Car:550”).

0.1 14 2 1 1 18

One hundred percent of the subjects whose

0.08 6 0 0 0 6 decreased VA was 0.4 passed the animal test

(norm

al value: 3/3: Cat:400", Rabbit: 200",

0/3 1/3 2/3 3/3 Total

Monkey:100") in the Titmus. In the results of the

circle test of the Titmus, subjects with VA of

0.32 were distributed widely from 0/9: (1/9:

800") to 9/9 (40") and 64% of the subjects with

1.0

0.8

0.64

0

0

0

0

0

0

0

0

0

1

8

14

1

8

14

VA of 0.62% obtained the best score of 9/9

0.5 0 0 0 12 12

(40"). Eighty-three percent of the subjects with

VA of 0.125 failed all tests.

0.4 0 0 0 12 12

0.3 2 0 2 11 15

3

Table 3.

The results of the circle test in the Titmus

Table 4

The results of the Animal test in the Titmus

9

9

0.25 3 0 1 6 10

0.2 1 3 0 5 9

0.15 11 0 2 3 16

0.125 5 0 0 0 5


Discussion

In this study we reduced VA of the non-dominant eye of normal subjects, as we estimated that

it would be more natural and possibly occurred in cases with amblyopia and strabismus whose

dominate eye always leads binocular vision. In normal subjects dominancy between two eyes

was not typical, yet all possessed each leading eye. In our study, we regulated VA of subjects,

but we were unable to regulate values of the stereotest. Therefore, we cannot evaluate this

study logically, but our results can be used clinically. The result of the circle test in the

Titmus(table 3) shows roughly a liner relationship between VA and stereotest, but at the same

time it presents a variety of results among each subject. For example, with a VA of 0.32

some subjects barely maintained stereoscopic vision, but on the other hand, others presented

perfect bifoveal stereopsis of 40". The result of the Lang test and Animal tests give rise to

simpler and more understandable results. With the Animal test in the Titmus(Table 4), for

example, all subjects with VA of 0.125 failed:0/3, (though still one subject obtained a normal

value of 3/3 even with VA of 0.1). All subjects whose VA was equal or better than 0.4

passed:3/3. Therefore, there are the thresholds of VA at which all subjects pass or fail the

stereo tests. However, when VA is between each end, the results of the stereo test are diverse..

We use the clinically minimum separable visual angle measured by the Landlt ring, but we

believe that in stereoscopic vision, vernier visual acuity, minimum distinguishable acuity, and

cognizancable acuity, also play important roles in establishing binocular fusion. These

fusional abilities differ among the individuals and attributes to the diversity of the stereotest

results. In the Lang test, subjects with VA of around between 0.15 to 0.32, 40 out of 50

subjects (80%) passed the test. This result supports the report that the Lang failed to screen 60

to 70% of children with amblyopia.

In conclusion, VA and stereoacuity is correlative yet there is much discrepancy among

subjects due to individual difference of fusional ability. Therefore, stereoacuity cannot be an

accurate indicator of VA, yet it gives rise to a gross estimation. Reduced VA of one eye

prevents people from maintaining binocular fusion. To establish stereoscopic vision, VA

equal or greater than 0.3 is required. With VA of 0.125 and below people lose stereopsis.

References

1. Wary SH. (1995). Optic Neuritis (Stereoacuity.) In Albert DM, Jakobiec FA(Ed.),

Principal and Practice of Ophthalmology (Vol.4 p.2545). Philadelphia: WB Saunders.

2. Lang JI, Lang TJ.(1988). Eye screening with the Lang stereotest. American Orthoptic

Journal, 38, 48-50.

3. Johnstone R, Brown S.(1995) A comparative assessment of the Lang, TNO & Titmus

stereotests. Australian Orthoptic Journal. 27-30.

4. Ohlsson J, Villarreal G, Sjostrom A, Abrahamsson M, Sjostrand J.( 2002). Screening for

amblyopia and strabismus with the Lang II stereo card. Acta Ophthalmol Scand. 80(2),

163-166.

5. Brown S, Weih L, Mukesh N, McCarty C, Taylor H.(2001). Assessment of adult stereopsis

using the Lang 1 Stereotest: a pilot study. Binocul Vis Strabismus Q, 16(2).91-98.

6. Romano PE, Romano, JA.(1973) Fusion. Anew classification and method for determing the

level of sensory binocular co-operation. Surv. Ophthalmol. 17. 458.

7. Levy, NS, Glivk EB(1974). Stereoscopic perception and snellen visual acuity. Am. J.

Ophthalmol, 78, 722-724

8. Hirai T, Yonekura Y. (1973) Suppression of anisometropic amblyopia observed in the

Titmus stereo test. (Article Japanese) Japanese Orthoptic Journal; 1(2) 15

4


Stereoacuity Following Unilateral And Bilateral Cataract

Extraction

Rebekah Lawry, Susie Sarangapani, Sheriden Graham, Mandeep Sagoo,

Carolyn Calcutt, Veronica Ferguson, Raj Maini.

Charing Cross Hospital, Fulham Palace Road, London W6 8RF. UK

Email:speckybeckyuk@yahoo.co.uk

Abstract

To assess stereoacuity for near and distance in patients undergoing cataract surgery and to

determine whether there is a need for second eye surgery in order to restore binocular

function.

Method: 44 consecutive patients undergoing cataract surgery at a single ophthalmic unit were

prospectively recruited over a 3-month period. Patients were divided into 2 groups: those

undergoing surgery to the first eye and those having second eye cataract surgery. All patients

had stereoacuity measured using the TNO test for near (480-15 secs of arc) and the Braddick

slides on the synoptophore for distance (720-90 secs of arc). Visual acuity for distance was

also measured. Testing was undertaken pre-operatively and at between 1 month and 6 months

post-operatively.

Results: Pre-operatively median visual acuity in the cataractous eye was worse in the 1 st eye

group, 6/18, but improved more significantly (p=0.001) to a median of 6/9 compared to the

2 nd eye group, which had a median of 6/9 but improving to a median of 6/6 (p=0.003). Preoperatively

60% of patients in the 1 st eye group had significant anisometropia, with a similar

finding of 58% of patients in the 2 nd eye group. Pre-operatively, overall, patients with

anisometropia had significantly reduced stereoacuity levels, but only for near (p=0.049).

However, there was a strong negative correlation between the degree of anisometropia and

distance stereoacuity levels (p=0.025).

There was a significant reduction in the number of anisometropic patients in the 2 nd eye group

(p=0.036) post-operatively, compared with the 1 st eye group where 50% of patients developed

or remained significantly anisometropic. There was no change in the median post-op near

stereoacuity in the 1st eye group, the 2 nd eye group, however, significantly improved to 240

secs of arc (p=0.037). Despite improvements in distance stereoacuity in both groups, there

was no significance found to relate this to anisometropia or visual acuity changes.

Conclusion: Despite the significant increase in visual acuity, more so in the 1st eye compared

to the 2 nd eye, and similar improvements in levels of stereoacuity in each group, the factor that

seems to determine stereoacuity levels is anisometropia. 1 st eye surgery seems unable to

significantly reduce the prevalence of anisometropia and the degree of anisometropia,

compared with 2 nd eye post-operative results, where the number of patients with

anisometropia significantly reduces, and a significant improvement in near stereoacuity

occurs.

Keywords

Visual acuity, stereoacuity, near, distance, anisometropia

Introduction

Stereoacuity is a measure of depth perception between objects when viewed binocularly.

Obstructions to stereoacuity include poor visual acuity in one or both eyes, ocular

1


misalignment or anisometropia. Patients with cataracts gradually develop poor visual acuity,

and due to myopic shift, anisometropia, which in turn causes loss or reduction of stereoacuity.

Removal of the cataract restores the visual acuity, but is this enough to restore stereoacuity, or

is second eye surgery required?

Methods

Initially 44 subjects were included in the study. Patients with a history of binocular imbalance

or any form of amblyopia or a history of any other ocular disease apart from cataracts were

excluded from the study. Verbal consent was obtained from all participants before testing

according to the guidelines of the Declaration of Helsinki. Cataracts were removed by phaco

emulsification and implanted with a posterior chamber IOL.

The patients were divided into 2 groups: those undergoing surgery to the first eye and

those having second eye cataract surgery. All patients had stereoacuity measured using the

TNO test for near (480-15 secs of arc) and the Braddick slides on the synoptophore for

distance (720-90 secs of arc). The TNO test uses red and green goggles to view random red

and green dot images held at 45cm. Both test plates were used to check stereoacuity was

present before going on to grade the depth of stereoacuity. A negative result was recorded

where after 1 minute of viewing no depth of stereoacuity could be numerically graded. Using

the synoptophore, at the corrected subjective angle, the Braddick slides allow distance

stereoacuity to be measured. These black and white random dot patterns on each slide when

superimposed produce a depth effect in the form of a letter or shape. Each slide is graded for

depth of stereoacuity. Where the grossest slide could not be identified after 1 minute of

viewing a negative result was recorded. Grading was from 720-90 secs of arc. Visual acuity

for distance was also measured on the Snellen vision chart at 6 metres. All testing was done

with best corrected acuity using either current glasses or trial frames after auto-refraction.

Testing was undertaken pre-operatively on the day of surgery and at between 1 month and 6

months post-operatively.

Data analysis required non-parametric statistical methods as both vision and

stereoacuity followed nonlinear progression. Snellen acuity was converted to a decimal value,

stereoacuity to a linear equivalent, where negative was assigned the value 1, 60 sec of arc

valued at 9. Wilcoxon signed ranks testing was used to compare visual acuity and stereoacuity

ranks of each group, and Kendall’s 1 tailed correlation method was used to analyse

anisometropia as a factor of stereoacuity.

Results

39 patients met the inclusion criteria and completed the follow-up. 3 patients were lost to

follow-up; one was unfit to continue in the study. In the 1 st eye group 20 patients remained,

equal male to female ratio, mean age 69 years, range 56-90 years. In the 2 nd eye group 19

patients remained, equal male to female ratio, mean age 77 years, range 59-100 years.

Pre-operatively median visual acuity in the cataractous eye was worse in the 1 st eye

group 6/18, (6/9-


Table 1

Pre-operatively Post-operatively Significance

Measurement Median Range Median Range

1 st eye group visual acuity 6/18 6/9-100 secs of arc) was achieved by 26% of

3


patients, but was not significant. Near stereoacuity in the 1 st eye remained at a median of 240

secs of arc post-operatively, with 30% of patients achieving fine central stereoacuity.

Despite an improvement in distance stereoacuity in both groups to a median of 360

secs of arc from negative, with 50% of patients improving in the 1 st eye group and 58%

improving in the 2 nd eye group, there was no significance.

Discussion

Unilateral cataract surgery success is well-documented (2) but review is needed to evaluate the

need for second eye surgery after previous successful first eye operation. There is now more

evidence available to support second eye surgery, (3) (4) the benefits of which are improved

quality of life, reduced visual symptoms, in addition to improved visual acuity and

stereoacuity. This study has shown that despite the more significant increase in visual acuity

post-operatively after 1 st eye than 2 nd eye surgery (4) , and similar improvements in levels of

stereoacuity both near and distance, the factor that seems to determine near stereoacuity is

anisometropia (4) There was evidence to suggest that the pre-operative degree of anisometropia

had affect on distance stereoacuity in this study. Fawcett et al (5) found significant failure rates

of foveal fusion at distance in patients with moderate anisometropia. First eye surgery did not

significantly reduce the prevalence of anisometropia and the degree of anisometropia (4)

leading to 20% of patients losing stereoacuity altogether. Compared, however, with the 2 nd

eye post-operative results, the number of patients with anisometropia significantly reduced,

and a significant improvement in near stereoacuity occurred. (6) Post-operatively in the 2 nd eye

group 25% of patients who had previously been anisometropic showed no change in near

stereoacuity levels, all remaining negative despite good visual acuity levels. These patients all

waited over 3 months with monovision before 2 nd eye surgery was done, suggesting continued

susceptibility of stereoacuity even after surgical correction of anisometropia. (5) Only 1 patient

in the 2 nd eye group lost stereoacuity. In this patient, post-operative visual acuity became

worse in the operated eye, and it is probable that due to the patient’s age of 100 years, there

were macula changes occurring. Kwapiszeski et al (7) found no patients lost stereoacuity postoperatively,

but anisometropic patients were discounted from their study.

Second eye surgery has been shown not only to significantly reduce anisometropia but

also to improve near stereoacuity.

Acknowledgements

Appreciation to ‘Joe’ C. Danchaivijitr for compiling the statistics.

References

1. Awaya I Y. 1980. Studies on aniseikonia and binocular fusion with special reference to stereoacuity. Nippon

Ganka Gakki Zasshi 84: 1619-1628

2. Desai P. 1993. The national cataract surgery survey: II clinical outcomes. Eye; 7: 489-94

3. Laidlaw D A H, Harrad R A, Hopper C D, Whitaker A, Donovan J L, Brookes S T, Marsh G W, Peters T J,

Sparrow J M. 1998. Randomised trail of effectiveness of second eye cataract surgery. The Lancet vol 352;

925-29

4. Elliot D B, Patla A E, Furniss M, Adkin A. 2000. Improvements in clinical and functional vision and quality

of life after second eye cataract surgery. Optometry and Vision Science. Vol 77, no 1, January:13-24

5. Fawcett S, Herman W, Alfieri C, Castleberry K, Parks M, Birch E. 2001. Stereoacuity and foveal fusion in

adults with longstanding surgical monovision. Journal of AAPOS vol 5; 342-7

6. Campos E C, Enoch J M. 1980. Amount of aniseikonia compatible with fine binocular vision: some old and

new concepts. J Pediatr ophthalmol strabismus. 17: 44-49

7. Kwapiszeski B R, Gallagher C C, Holmes J M. 1996. Improved stereoacuity: An indication for unilateral

cataract surgery. J Cataract refract Surg vol 22, May: 441-445

4


Measurement And Improvement Of Visual Skills In Young Adults

Yoshie Morita 1 , Akiko Toshimitsu 2 , Mitsuko Shima 2 , Maureen Powers 1

1 Gemstone Foundation Research Institute, Rodeo, CA , USA, 94572, 2 Tokyo College of

Medico-Pharmaco Technology, Tokyo, Japan. Email mamori71@aol.com

Keywords

Visual skills, prevalence, accommodative facility, vergence, binocular vision

Introduction

This study aimed to measure visual skills that may be related to reading in college students in

Japan, a population for which no standards exist. We intended this study to be a pilot for

determining visual skill norms in Japan, and for determining whether an inexpensive, internet

visual skills training program 1 can help students in need.

Method

Vision and visual skills testing for 61 orthoptic students (avg. age 20 yr., 95% female)

included: visual acuity (far and near), refractive errors(auto-refractometer), Titmus Stereo

Test, binocular balance (far and near), near point of convergence (NPC), near point of

accommodation (NPA), prism vergence at near (Base In, Base Out, break/recovery),

accommodative facility at near ( + 2.00D, monocular)(AF), Developmental Eye Movement

test (DEM) 2 , and symptom list.

All visual skills were measured with their habitual glasses/CL. Four cases were

excluded due to ocular disease history. All students were asked to participate in an internet

vision training program (cVST) 1 . Under this program, students completed 30 sessions, 20

minutes/day at least three times a week. The same screening tests were given after program

completion.

Results

Prevalence: All students were 20/20 at far with correction. Figure 1 shows refractive errors.

43 students (75.1%) exceeded -1.00 Diopters, and the overall average was -3.21D (Figure 1).

52 students (91.2%) were 20/20 with their glasses/CL at near and 5 students (8.8 %) were

between 20/30 and 20/25 in either eye. 55 students showed 40” of arc and two showed 60”

and 80” of arc in stereo test.

No.of Students

20

15

10

5

0

Fig 1: Refractive Errors

over+3.00

0-+0.25

under -1.00

-1.00


Figure 2 shows the result of phoria far and near. 14 students (24.6%) were exophoric

at both far & near, 18 students (31.6%) were exophoric only at near and 1 student (1.8%) was

esophoric only at near.

Based on Morgan’s criteria 3 , 7 (12.3%) students were “out of normal range” with

more than 4X pd at far, 12 (21.1%) with more than 8X pd, and 1 with more than 2E pd at

near.

Prism vergence Base Out average was 38.04 pd for break and 30.84 pd for recovery;

Base In averaged 15.93 pd for break and 11.33 pd for recovery. See Fig 3A, 3B. NPC avg.

was. 4.4 cm (3 to 11cm). NPA avg. was 8.6 cm (5 to 15cm).

Fig 3A: Vergence (Base Out)

50

40

PD

30

20

10

0

recovery

break

Fig 3B: Vergence (Base In)

30

25

20

PD

15

10

5

0

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55

The DEM Ratio of 12 students (21.1%) was above 1.24, which is 2 standard

deviations slower than normal (Figure 4). Vertical average time for DEM was 23.40 sec

(17.05 to 31.01 sec), horizontal average time was 26.64 sec (17.95 to 40.20sec), and the ratio

averaged 1.14 (0.13 sd). Average Accommodative Facility was 12.32 c/m (range 0 to 23)

(Figure 5).

.

No. of Students

20

15

10

5

0


Table 1

Criteria for visual skills and Number of students classified as “weak”

BI break


overwhelmingly female; thus, clearly more work needs to be done to determine whether our

results might apply to male students as well. Nonetheless, our results are in agreement with

others showing a high amount of myopia among young Japanese < today. They are also in

agreement with regard to exophoria: 56% of students in this sample were exophoric at near,

which also seems high, and may or may not be related to myopia • . The Base Out vergence

and NPC values were showed remarkably strong 7 , but the Base In result was relatively weak

both in break and recovery, in spite of the fact that there were many exophoric students.

The prevalence of problems with AF, and with the DEM, was remarkable. In 4 cases,

these academically accomplished students could not facilitate even 1 cycle within 1 minute.

During the test, many subjects had a particularly hard time dealing with +2.00D compared to

– 2.00D. These are very poor values regardless of the criterion one s selects ‚ƒ6 . As for the

DEM, students who have learned to read vertically may take particular care not to make

mistakes in horizontal reading, which may affect the result. Since these two tests (AF and

DEM) are relatively new to Japanese people, we need to collect data from more subjects to

determine whether these findings are general in the population.

The cVST result shows improvement after Treatment. However, some No-Treatment

Control subjects also improved, and the reasons for their improvement need to be examined.

Overall many students felt improvement in vergence and comfort. It is possible that we are

not adequately measuring important variables that describe their conditions and subsequent

improvement.

This study measured a set of basic eye conditions and visual skills in Japanese young

adults. However in daily life, such individual skills must function together to achieve specific

visual tasks. For example, even though a student has excellent convergence skills, or

“perfect” 20/20 visual acuity, he or she may still have difficulty reading. And in some cases

that difficulty can be related to visual skills. In the course of this study we found 2 students

who realized they had reading problems since childhood. For example, they felt different

from their peers while studying. Without this study they would not have a chance to consider

their problems are, and they would continue to be hidden. Both of theses students completed

cVST and both improved their weak visual skills. One improved dramatically after tracking

training binocularly. Now she enjoys reading.

The prevalence of such extreme reading problems, related to visual skills, in such an

educated population as orthoptics students, may seem small: only 3.5%. But this value

matches the general prevalence of strabismus and amblyopia, and thus deserves more

attention than it now receives from scientists, orthoptists, and the public at large.

Acknowledgments

We thank the Gemstone Foundation for its continued support of reading-related vision

problems, and the students and staff of the Tokyo College of Medic –Pharmaco Technology.

References

1. Grisham, D., Powers, M., Epstein, G. & Riles, P. (2002). Visual skills screening and computerized training of

underachieving high school students. Manuscript submitted for publication

2. R. P., Richman, J. E., Nicholson, S. B. & Gaines, C. S. (1990). A new visual-verbal saccade test: the

Developmental eye movement test (DEM). J Am Optom Assoc 61(2),124-135.

3. Morgan, MW, Analysis of clinical data,.(1944) Am J Optom Arc Am Acad Optom 21 477-491

4. Tokoro T. (Ed) (1992) Kussetu ijou to sono kyousei Kanehara shuppan

5. Yamashita M., Tokoro T.: (1987) Kussetu joutai to gani-ijou, J. A.S.A Vol14.161-165

6. Zallers J. A, Alpert T.L, Rouse M. W.(1984) A review of the literature and a normative study of

accommodative facility J. of Amer Opto Ass Vol 55 No.1, 31-37

7. Powers M,, Morita Y. (2004) Large differences between Japanese and US students in convergence break and

recovery. Paper presented at ARVO.

4


Diagnosis And Treatment In Patients With Asthenopic Symptoms

Due To Exophoria

Birgitta Neikter

Brigitte Eriksson-Derouet

Department of Clinical Neuro Sciences

Karolinska Institutet

S:t Eriks Ögonsjukhus

SE-112 82 Stockholm

Sweden

birgitta.neikter@ste.ki.se

Abstract

Patients with asthenopia complain most commonly of headache, tiredness in fixating,

problems in changing focus and diplopia at near fixation. The aim of the study was to

determine proper methods to diagnose patients with asthenopic problems and to separate them

from patients with similar problems from other causes. The study included 109 patients, 79

women and 30 men. All the patients had an orthoptic investigation including history, visual

acuity and assessment of binocular single vision, accommodation, retinoscopy and/or

subjective refraction in cycloplegia. Diagnostic occlusion and a careful prism-adaptation test

were also performed. Prism glasses were prescribed and had to be changed from time to time,

due to increase of the angle of strabismus and symptoms. In about 1/3 (36) of the patients in

this study the angle of squint increased so that surgery was necessary.

Keywords

Asthenopia, prism glasses, operation, resection, recession.

Introduction

Asthenopia is a common condition in modern’s society and the number of patients with

asthenopic problems has increased probably due to stronger psychosocial demands on visual

performance [1,2]. Many of these patients have additional psychological problems [3] and

often they are incapable of working [4, 5].

Patients with asthenopia mainly complain of pain around the eye(s) and headache,

mostly in the frontal and temporal regions. They sometimes also describe dizziness and

blurred vision, and the symptoms may also include pain in the gastro-intestinal area, in the

back and shoulders. The patients complain of being tired when doing visual near work, but

also when driving a car or watching TV. Both adults and children may have asthenopic

problems. Children have other symptoms, such as attention problems and unwillingness to

read or to do other types of near work [6, 7]. In most patients the asthenopic symptoms are

developing when they have to read with higher intensity than before, thus during the last years

of school and in college or at university [3].

Asthenopia is thought to represent disturbances in the sensory- motor system [8]. Such

anomalies may be a heterophoria, disturbed function of the extraocular muscles or poorly

corrected refractive errors including anseikonia [3]. Asthenopic symptoms may appear when

compensation-mechanisms for these anomalies become insufficient.

1


Material and Methods

Inclusion criteria for the patients of this study were asthenopic symptoms, such as headaches,

tiredness, dizziness, double vision, blurred vision (i.e. problems in focusing when shifting

fixation from far to near).

Patients with heterotropia, paretic strabismus, amblyopia, pathological nystagmus or

other ophthalmological diagnoses or headache related to diseases were excluded from the

study.

The study population included 109 patients, 79 women and 30 men, with a median age

of 30 years and an age range between 9 and 67 years of age. Diagnostic occlusion in cases

with unclear orthoptic results. It was applied on the non-dominant eye for three to ten days

[9].

Statistical differences were tested with Wilcoxon Signed Ranks Test and analysis of

variance (General Linear Model).

Results

Most of the patients complained of several symptoms. Some of the patients had problems

after only a short time of near work and others late in the afternoon or evening (57%). A small

number (13%) stated problems in the morning. The most common symptoms were tiredness

and headaches after near work (71%), also strain in the head, forehead, face- and eye muscles

(61%). Diplopia was found mostly at near (34%). Other common symptoms were migraine

headache (13%), neck problems (11%), blurred vision (12%), focusing problems (14%) and

dizziness (15%). Less common symptoms were grinding of the teeth (0,8%), pains in the

stomach (3%) and back (6%).

We also noted that patients with poor near point of convergence at the first

consultation had an almost normal convergence after wearing refraction with prisms. The

changes were statistically significant (p=


Reduction of asthenopic symptoms - patient satisfaction

Treatment with prisms and surgery gave subjective improvement 97 (89%) of the patients.

Ten (9%) of the patients were partially satisfied and 2 (1,8%) not at all (fig 2). The patients

were after treatment free from asthenopic symptoms (such as headache and strain) and also

felt comfortable in focusing for near and distance. Those who still had problems were

continuously treated.

89%

9%

1,8%

Satisfied Part satisfied Not satisfied

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

Figure 2 Subjective improvement in all 109 patients.

In summary, this study shows that this group of patients with asthenopic problems is

much larger than we previously thought. Only ten years ago the treatment of these types of

patients was to treat fusion ability and convergence. The patients felt comfortable for 3-6

months, but they always returned for a new period of treatment. The majority of the patients

were women. We have also observed that patients with long standing asthenopic problems

were difficult to diagnose and treat. In these cases it is very important to listen to the patient

and to try to understand the whole situation. The most common refractive error was

hypermetropia, but only half of the patients had correct spectacles. It is important to discover

an exophoria that is controlled with the accommodative convergence, resulting in an

orthophoria or even an esophoria. In children it is also important to differentiate between an

exophoria with asthenopia combined with reading-problems, and true dyslexia. The

differentiation can be made after an adequate orthoptic/ ophthalmological investigation in

these children.

Discussion

In this investigation of 109 patients with asthenopic problems it has been shown that after a

thorough orthoptic investigation all of them had a heterophoria, and always an exophoria. The

exophoria is compensated by the accommodative convergence [10, 11] and not only with the

help of motor fusion.

Some of the patients (12/109) in our study belong to the hypo-accommodative group.

Costenbader [12] divided the non-refractive accommodative convergence excess into two

groups (hyper kinetic and hypo-accommodative) where hyper kinetic is classified as the

esodeviation that we refer to as the convergence excess type i.e. with a large esophoria/tropia

at near and without problems. Characteristic for both groups is the disproportion between

accommodation and convergence. The hypo-accommodative group is more rare and is often

discovered later than the hyper kinetic one, which is successfully treated with bifocals with a

3


large near section. The hypo-accommodative type is more difficult to diagnose and can appear

as a pathophoria, exophoria, esophoria or/and in combination with a vertical deviation.

An important diagnostic test is the ”4∆ basein test” introduced by Mühlendyck (11,

13) and Rüssman (14, 13). The “4∆ basein test” is a quick diagnostic test. All patients

responded to it by reporting relief of asthenopic symptoms, either immediately or after

wearing the prisms for some time.

Acknowledgements

Thanks to the orthoptists in the clinic who helped us with orthoptic investigations.

References

1. CALCUTT, C., KINNEAR, P.:

Accommodative defects in children and young adults. Br Orthopt J, 54:58, 58-60; 1997.

2. CHROUSOS, G. A., O´NEILL, J. F., LUETH, B. D., PARKS, M. M.:

Accommodation Deficiency in Healthy Young Individuals. J. of Ped. Ophth. & Strab., Vol 25, No. 4, 176-

179, 1988.

3. von NOORDEN, G.K., CAMPOS, E. Binocular vision and Ocular Motility: Theory and management of

strabismus. - 6 ed. - St. Louis: Mosby, 2001. -672 s.

4. JAMES, E.L.:

Hypo-accommodative esotropia. Br Orthopt J, 54:54, 54-57; 1997

5. PETRUNAK, J.:

Spasm of the Near Reflex. Am. Orthoptic J., vol 37,122-1125,1987.

6. MATSOU, T., OHTSUKI, H.:

Follow-up results of a combination of accommodation and convergence insufficiency in school-age children

and adolescents. Graefe´s Arch. Clin. Exp. Ophth. 230, 166-170, 1992.

7. MÄNTYJÄRVY, M.,I.:

Accommodation in hyperopic and myopic Schoolchildren, J. of Ped. Ophth. & Strab., Vol 24, No. 1, 37-41,

1987.

8. WALSH, F.B., HOYT, W.: The Neurology of Accommodation: the motor system for the ciliary muscle

Clinical Neuro-Ophthalmology Vol 2., 4 ed. the Williams & Wilkins Comp. Baltimore, p.534-551, 1985.

9. NEIKTER, B.:

Horizontal and vertical deviations after prism neutralization and diagnostic occlusion in intermittent

exotropia, Strabismus Vol. 2, No.1, 13-22, 1994.

10. von GRAEFE, A.:

Ueber musculäre Asthenopie. V. Gaefes Arch. Ophth. N:o 8, 314-367, 1862.

11. MÜHLENDYCK, H., et al.:

Konvergenzexzess bei juveniler Akkommodationsschwäche Schielen Nr. 12, Wiesbaden 1979, 117-128,

1980.

12. COSTENBADER, F. D.:

Clinical course and management of esotropia.

Strab. Ophth. Symp. 11 St. Louis, The CV Mosby Co, 325-353, 1958.

13. MÜHLENDYCK, H., RÜSSMANN, W., REINBOTH, J.:

Der 4 Prismendioptrien-Basis-innen-Test in der Diagnostik von Exophorien mit Asthenopie und

Kompensation über die akkommodative Konvergenz. Ophthalmologe 90, 6-10, 1993.

14. RÜSSMANN, W.:

Heterophorie (latenter Strabismus). Strabismus, Enke, Stuttgart, ed. Kaufmann H, de Decker, W., Friedburg,

D., Haase, W., Komerell, G., Rüssmann, W., 121-136, 1986.

4


Monovision By Implanted Intraocular Lenses

Marie Nitta a , Takahiro Niida b , Risako Higa a , Kimiya Shimizu a

a Department of Ophthalmology, Kitasato University Hospital,

1-15-1 Kitasato, Sagamihara, Kanagawa, 228-8555 Japan

b Department of Orthoptics and Visual Science, School of Health Science, International

University

of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara ,Tochigi, 324-8501 Japan

Marie-n@mve.biglobe.ne.jp

Abstract

Purpose: Monovision by implanted intraocular lenses (IOL) compensates for loss of

accommodation after cataract surgery. We evaluated the visual function and patient

satisfaction of monovision by IOL.

Methods: The subjects were 84 patients (17 males, 67 females). The mean age was 68 years

old. All subjects had informed consent and applied to our criteria, their dominant eye

determined by the hole-in-card-test was corrected for distance and the other eye was corrected

for near. Visual acuity at all distances, contrast sensitivity, fusional amplitude and

stereoacuity were measured. Questionnaire was used as assessment of satisfaction.

Results: The mean amount of anisometropia was 2.53 D. The binocular visual acuity at all

distances was 20/25 or better, especially at middle distances the binocular visual acuity

showed binocular summation. The contrast sensitivity at low and middle spatial frequencies

also showed binocular summation. The stereoacuity was 80 seconds of arc and the fusional

amplitude was 44.7 prism diopter. 77.4% of patients satisfied monovision.

Conclusion: Monovison by IOL was considered effective method to compensate for loss of

accommodation after cataract surgery.

Keywords

Monovision, IOL, Visual acuity, Binocular function, Satisfaction

Introduction

Monovision is one of a strategy to compensate for presbyopia in which one eye is corrected

for distance vision and the other is corrected for near vision (1). Monovision by contact lens

has become popular and recently monovision has applied to refractive surgery (2, 3).

On the other hand, the loss of accommodation after cataract surgery is a severe

problem. Since 1999, we have tried to overcome this problem by monovision with bilateral

cataract surgery. In this study, we evaluated the visual function and patient’s satisfaction of

monovision by IOL.

Material and Methods

The subjects were 84 patients (17 males and 67 females) who performed monovision by IOL

from May 1999 to April 2004 at Kitasato University Hospital. Their average age was 68 years

old (29 ~ 86 years old), and the average period of follow-up was 19 months (1 ~ 59 months).

All subjects had informed consent and applied to our criteria, their dominant eye determined

by the hole-in-card-test was corrected for distance and the other eye was corrected for near.

1


Visual acuity at all distances (AS-15, KOWA), contrast sensitivity at middle distance,

fusional amplitude and near stereoacuity (Titmus stereo tests) were measured. Questionnaire

was used as assessment of satisfaction.

Results

The average refraction of dominant eye was 0.11 D (-0.50 ~ +0.88 D) and that of

nondominant eye was -2.41 D (-1.50 ~ - 4.00 D). The mean amount of anisometropia was

2.53 D (1.50 ~ 4.25 D).

The binocular visual acuity was 20/25 or better at all distances and especially

binocular visual acuity at middle distances (0.7 m and 1.0 m) was greater than the monocular

visual acuity (Fig.1).

At low spatial frequencies (0.5 ~ 2.0 cpd), the binocular contrast sensitivity was

greater than the monocular contrast sensitivity and it was statistically significant. At high

spatial frequencies (greater than 4.0 cpd), the binocular contrast sensitivity was equal to or

below the monocular contrast sensitivity (Fig.2).

The median of stereoacuity in monovision was 80 seconds of arc (40 ~ 800 seconds of

arc) and 40 seconds of arc (40 ~ 200 seconds of arc) under full correction of refractive error.

81 % of patients, the stereoacuity was better than 100 seconds of arc (Fig.3).

The mean of fusional amplitude in monovision was 44.7 prism diopter (10 ~ 84 prism

diopter) and 64.9 prism diopter (22 ~ 118 prism diopter) under full correction of refractive

error (Fig.4).

77.4% of patients satisfied monovision. The rate of using glasses was 15.5%.

Discussion

It is well known that less than + 1.50 D add power is recommended in monovision with

contact lens (2) or LASIK (3). This study revealed that best add power in monovision by IOL

is +2.25 ~ +2.50 D since pseudophakic patients lost their accommodation completely.

Binocular visual acuity at middle distance was obviously better than each monocular visual

acuity. Thus, it indicates obvious binocular summation of visual acuity was observed in

middle distance. In contrast, anisometropic blur reduced binocular summation of contrast

sensitivity, particularly at high spatial frequencies, since blurred image lacks high frequency

detail (4). It has been indicated that the suppression of anisometropic blur plays an important

role in binocular summation (4, 5). It seemed that the difference of binocular summation

between visual acuity and contrast sensitivity was due to a discrepancy of each stimulus

condition such as contrast, background luminance and optical arrangement of device.

Although stereoacuity in monovision reduced as compared to that of under full correction of

refractive error, 81 % of patients showed within normal limits. Consequently, 77.4% of

patients were satisfied monovision. This value is in good agreement with the previous report

(6). However, some patients complained about asthenopia and reduced near or middle

distance acuity. Larger add power and / or larger interocular differences in visual acuity must

inevitably reduce binocular visual functions. Likewise, strong ocular dominance interrupts

blur suppression as well as the switching of eye, i.e., smooth alternation of fixation.

In summary, most of patients showed good visual quality and were satisfied with

monovision. Therefore, it is strongly suggested that monovison by IOL is effective method to

compensate for loss of accommodation after cataract surgery. Careful selection of patients as

well as precise measurement of IOL power is needed to improve patient’s satisfaction

furthermore.

2


Acknowledgements

This study was supported in part by Grant from the Ministry of Education, Science, Sports,

Culture, and Technology, Japan (T. Niida; No.14571686).

References

1. Fonda, G. (1966). Presbyopia corrected with single vision spectacles or corneal lenses in preference to bifocal

corneal lenses. Trans Ophthalmol Soc Aust, 25, 78-80.

2. Jain, S., Ou, R., Azar, DT. (2001). Monovision outcomes in presbyopic individuals after surgery.

ophthalmology, 108, 1430-1433.

3. Wright, KW., Guemes, A., Kapadia, MS., et al. (1999). Binocular function and patient satisfaction after

monovision induced by myopic photorefractive keratectomy. J Cataract Refract Surg, 25, 177-182.

4. Schor, C., Landsman, L., Erickson, P. (1987). Ocular dominance and the intraocular suppression of blur in

monovision. Am J Optom Physiol Opt, 64, 723-730.

5. Collins, MJ., Brown, B., Bowman, KJ. (1989). Contrast sensitivity with contact lens corrections for

presbyopia. Ophthaimic Physiol Opt, 9, 133-138.

6. Jain, S., Arora, I., Azar, DT. (1996). Success of monovision in presbyopes: review of the literature and

potential applications to refractive surgery. Surv Ophthalmol, 40, 491-499.

Fig.1. Visual acuity at all distances.

Fig.2. Log contrast sensitivity as a function of spatial frequency.

3


Fig.3. Stereoacuity measured by Titmus stereo tests at 40 cm.

Fig.4. Fusional amplitude measured by major amblyoscope.

Fig.5. Satisfaction.

4


The Effect Of Simulated Torsional Disparity On Horizontal

Fusional Vergence And Stereopsis In Normal Subjects.

Michael Sleep, Zoran Georgievski

School of Orthoptics, La Trobe University

Bundoora Victoria 3086 Australia

michaelsleep@hotmail.com, z.georgievski@latrobe.edu.au

Abstract

Purpose. To explore the extent to which increasing torsional disparity affects horizontal

fusional vergence and stereopsis. Methods. Increasing excyclotropia was simulated at a

synoptophore on 21 normal subjects and the horizontal fusional amplitudes and stereoacuity

were assessed. Results. The differences between the mean baseline fusional divergence and

mean amplitude at 6 ° of simulated excyclotropia (SE) reached statistical significance, and

similarly with convergence. Finer levels of stereopsis were decidedly affected at greater than

4 ° of SE, with the more gross levels affected beyond 6 ° . Conclusion. Despite patients having

the sensory capacity to fuse up to and beyond 10 ° of torsion, better torsional re-alignment

surgically would result in greater BSV function and fewer related symptoms.

Keywords

torsion, cyclotropia, fusional vergence, stereopsis, binocular single vision.

Introduction

Adaptations to horizontal disparity and, to a lesser extent, vertical disparity, have been

investigated by many researchers. Perhaps the least researched, and as a consequence the least

understood, is the effect that torsional disparity has upon binocular single vision (BSV). The

aim of the present study was to explore the effect of simulated excyclotropia (SE) on two

clinical measures of BSV: horizontal fusional vergence and stereopsis. The hypothesis was

that there will be a gradual decrease in these measures as the level of SE increases.

Several researchers have speculated about and investigated fusion amplitudes in the

torsional plane. Lyle (1951) indicated that approximately 6 o -10 o of either incyclotropia or

excyclotropia could be overcome via torsional fusional reserve.(1) Watts’ (1972) findings

concurred with this - in a study of 49 normal subjects, no more than a mean of 8 o of

incyclotropia or excyclotropia could be tolerated.(2) Subsequent authors and researchers have

reported somewhat higher torsional fusion amplitudes. Veronneau-Troutman (1972) carried

out an investigation of torsional fusion amplitudes and found that subjects were able to fuse

an average of 16.8 o of SE and 11.8 o of simulated incyclotropia.(3) Jampel et al (1975)

investigated the motor and sensory components of torsional fusion and found that up to 22 o of

torsional disparity was “easily fused”.(4) Guyton (1987) claimed that up to 15 o of torsional

disparity could be fused by combining sensory fusion of 8 o allowed by Panum’s peripheral

fusional areas and torsional motor fusion responses of 6-8 o observed by other researchers.(5)

Pratt-Johnson and Tillson (1987) reported that torsion of greater than 10 o or bilateral

torsion interrupted BSV in a series of patients with bilateral superior oblique palsy (SOP).(6)

This was most likely due to a large increase in excyclotropia in down gaze, as demonstrated

by Kraft et al (1983) and Georgievski and Kowal (1995), both measuring an increase in the

mean excyclotropia from primary position to down gaze of 57% and 100%, respectively, in

patients with bilateral SOP.(7,8)

1


Materials and Methods

The sample comprised 21 adult subjects (mean age 26.4 years, range 18-38 years) and their

suitability for participation was determined using the following criteria: uncorrected visual

acuity of 6/9 or better; no manifest deviation or significant (>10 ∆ ) heterophoria; no

extraocular muscle imbalance; and stereoacuity of at least 550 seconds of arc (”) (Lang test).

A Clement Clarke synoptophore (Model 2053), Series F fusion slides and Braddick

random dot graded stereo slides was used to simulate excyclotropia and assess horizontal

fusional vergence and stereoacuity.

A ‘baseline’ assessment of horizontal fusional vergence was performed without any

simulated excyclotropia (SE), followed by assessment at 5 levels of unilateral SE. These 5

levels ranged from 2 o to 10 o in increments of 2. Each subject was instructed to report the point

at which horizontal diplopia was first recognised whilst their visual axes were encouraged to

initially diverge and subsequently converge. Fusional vergence was measured objectively and

subjectively and repeated twice at each level.

A baseline assessment of stereoacuity was performed without any SE, again followed

by assessment at 5 levels of unilateral SE. At each, the subject was presented with the random

dot stereoscopic images and asked to identify the symbol depicted and nominate whether it

was raised or sunken (according to crossed and uncrossed disparity conditions) relative to the

surrounding random dots. Three separate images were presented at each level of stereoacuity

and success was defined as at least 2 correct answers out of the 3.

Results

The mean baseline fusional divergence amplitude, that is, without SE, was 6.09 (range 3-

10 , SD 1.81). As the SE increased, the mean fusional divergence amplitude decreased, with

the lowest mean measurement at 10 o of SE (2.76 , range 0-6 , SD 1.60) (Table 1).


Table 1. Mean fusional divergence amplitude at baseline and varying levels of SE.

SE Mean fusional div. amp. SE (cont.) Mean fusional div. amp. (cont.)

Baseline (0 o ) 6.09 (+/- 1.81) 6 o 4.28 (+/- 1.67)

2 o 5.33 (+/- 1.88) 8 o 3.71 (+/- 1.73)

4 o 5.09 (+/- 1.78) 10 o 2.76 (+/- 1.60)

Pairwise comparison between the mean baseline fusional divergence amplitude and

the mean at the varying levels of SE showed that there were statistically significant

differences between the baseline measurement and 6 o of SE or greater (Table 2).


Table 2. Pairwise comparison between the baseline mean amplitude of fusional divergence and means at each

level of SE.

Baseline (B) Excyclotropia (E) Mean difference (B-E) Significance

0 o 2 o 0.76 1.000

4 o 1.00 0.087

6 o 1.81 0.002

8 o 2.38 0.000

10 o 3.33 0.000

Similar to the fusional divergence results, the mean baseline fusional convergence

amplitude was highest, 41.42 (range 14-90 , SD 24.52), with the lowest mean measurement

at 10 o of SE (13.81 , range 4-42 , SD 10.65) (Table 3).

Pairwise comparison between the mean baseline fusional convergence amplitude and

the mean at the varying levels of SE showed similar results to those found with fusional

divergence. Statistically significant differences were reached between the baseline

measurement and 8 o of SE or greater (Table 4).

2


Table 3. Mean fusional convergence amplitude at baseline and varying levels of SE.

SE Mean fusional conv. amp. SE (cont.) Mean fusional conv. amp. (cont.)

Baseline (0 o ) 41.42 (+/- 24.52) 6 o 25.71 (+/- 18.75)

2 o 33.38 (+/- 19.53) 8 o 21.00 (+/- 14.57)

4 o 28.38 (+/- 15.63) 10 o 13.81 (+/- 10.65)


Table 4. Pairwise comparison between the baseline mean amplitude of fusional convergence and means at each

level of SE.

Orthophoria (O) Excyclotropia (E) Mean difference (O-E) Significance

0 o 2 o 8.04 0.806

4 o 13.04 0.063

6 o 15.71 0.056

8 o 20.42 0.002

10 o 27.61 0.000

All subjects achieved stereoacuity of 90” without any SE, as was the case at 2 o of SE.

At 4 o of SE, the first effects of the torsional disparity on stereoacuity became evident with 3

subjects (14.3%) no longer being able to appreciate the random dot slide images representing

90”. Of these 3 subjects, 2 were still able to appreciate stereoacuity of 180” and the remaining

subject was only able to appreciate gross stereopsis representing 360” or greater.

At 6 o of SE, 9 subjects (42.9%) were able to appreciate stereoacuity of 90”. Of the

remaining 12 subjects; 3 achieved stereoacuity of 180”; 3 identified the images representing

360”; 1 had stereoacuity of 720”; and 5 (23.8%) were not able to achieve any stereopsis.

At 8 o of SE, 4 subjects (19%) were still able to identify images representing 90”. Of

the remaining subjects, 1 (4.8%) had stereoacuity of 180” and 16 (76.2%) were not able to

achieve any stereopsis. At 10 o of SE, no stereopsis was achieved by any but 1 subject, who

unexpectedly maintained stereoacuity of 90”. This result was obviously an outlier.

Discussion

Two papers published in the last decade are particularly important as far as the present study

is concerned. The first is by Sharma et al (1999), who reported that baseline horizontal

fusional vergences decreased once levels of simulated torsion reached approximately 4 o .(9)

Their findings were indicative of a gradual decrease in horizontal fusional vergences across

the range of torsional fusion, the mean torsional fusion amplitudes being about 13 o . The

present study supports the findings of Sharma et al (1999) and expanded on them to provide a

more definitive explanation of the effect of SE on horizontal fusion.

The second study is by Yagasaki et al (1994), who explored stereoacuity in the

background of torsional disparity and found that a random dot stereoscopic image of 125”

could not be appreciated beyond 4 o of SE.(10) However, a coarse disparity of 805” was able

to be appreciated with up to 9 o of SE. The present study bridges the knowledge gap between

such fine and coarse stereoacuity levels.

The findings of the present study can be summarised as follows. With respect to

fusional divergence, the baseline measurements became statistically significantly affected at

6 o of SE, though even at 4 o of SE the significance level was 0.087. Similarly with fusional

convergence; the baseline measurements came statistically significantly affected at 8 o of SE,

though at 6 o and even 4 o of SE the significance levels were 0.056 and 0.063, respectively,

indeed close to the set alpha of 0.05. Certainly, these mean measurements relative to the

baseline were conspicuous from a clinical perspective.

With respect to stereopsis, there was no deterioration of stereoacuity with 2 o of SE.

Nor did 4 o of SE have a significant effect - 18 subjects (86%) appreciated stereoacuity of 90”,

and 20 subjects (95%) appreciated stereoacuity of 180”. Beyond 4 o of SE, there was a marked

decrease in the number of subjects able to appreciate the finest (90”) level of stereoacuity. At

3


6 o of SE, only 9 subjects (43%) could appreciate 90”, while 20 (95%) still appreciated 180”.

At 8 o of SE, a mere 4 subjects (19%) appreciated 90”, while the number that appreciated 180”

dropped to 5 (24%).

Similar to the findings of Yagasaki et al (1994), this ‘threshold’ of 4 o was increased

with the larger disparities. At 4 o of SE, all subjects (as opposed to 86%) appreciated

stereoacuity of 360” and 720”. At 6 o of SE, 15 subjects (71%, as opposed to 43%) appreciated

stereoacuity of 360” and 16 subjects appreciated stereoacuity of 720”. Beyond 6 o of SE, there

was a marked decrease in the number of subjects able to appreciate these coarser levels of

stereoacuity. At 8 o of SE, only 5 subjects (24%) appreciated stereoacuity of 360” and 720”.

By combining these results with those of Yagasaki et al (1994), it appears that excyclotropia

beyond 4 o significantly impacts on the abilities of most individuals to appreciate finer levels

of stereopsis, whilst greater disparities become affected with a slightly greater threshold of 6 o .

Conclusion

The findings of this study impact on the way treatment of torsion and excyclotropia in

incomitant strabismus should be tackled. Some researchers assessing the surgical management

of torsion appear to rate successful treatment as elimination of torsional diplopia (Pratt-

Johnson and Tillson, 1987; Price et al, 1987).(6,11) Whilst this is largely correct and should

be an aim of surgery, the findings of this study would suggest that success should be qualified

with regard to the well-being and function of the fusional vergences and stereopsis

mechanisms, since both are integral to the patient having comfortable BSV. Therefore,

surgery for torsion should be aimed at reducing torsion to at least (or a maximum of) 6 o , and

for optimum binocular vision results, to at least 4 o .

References

1. Lyle, K. T. (1965). Cyclotropia due to bilateral superior oblique palsy caused by head injury.

British Orthoptic Journal, 22, 2-10.

2. Watts, R. (1972). The assessment of cyclotropia in paralytic squint. In J. Mein, Bierlaagh J.J.M.,

Brummelkamp-Dons, T.E.A. (Ed.), Orthoptics. Proceedings of the Second International Orthoptic

Congress (1971) (pp. 309-316). Amsterdam: Excerpta Medica.

3. Veronneau-Troutman, S. (1972). Cyclotropia. American Orthoptic Journal, 22, 36-43.

4. Jampel, R. S., Stearns, A., Bugola, J. (1976). Cyclophoria or cyclovergence: illusion or reality? In

S. Moore, Mein, J., Stockbridge, L. (Ed.), Orthoptics: Past, Present, and Future. Proceedings of

the Third International Orthoptic Congress (pp. 403-408). New York: Grune and Stratton.

5. Guyton, D. L. (1987). Ocular torsion: sensorimotor principles. American Orthoptic Journal, 37,

13-20.

6. Pratt-Johnson, J. A., Tillson, G. (1987). The investigation and management of torsion preventing

fusion in bilateral superior oblique palsies. Journal of Pediatric Ophthalmology & Strabismus,

24(3), 145-150.

7. Kraft, S. P., O'Reilly, C., Quigley, P.L., Allan, K., Eustis, H.P. (1993). Cyclotorsion in unilateral

and bilateral superior oblique paresis. Journal of Pediatric Ophthalmology & Strabismus, 30, 361-

367.

8. Georgievski, Z., Kowal, L. (1995). A survey of symptomatic ocular torsion. Strabismus, 3(4), 169.

9. Sharma, P., Prasad, K., Khokhar, S. (1999). Cyclofusion in normal and superior oblique palsy

subjects. Journal of Pediatric Ophthalmology & Strabismus, 36(5), 264-270.

10. Yagasaki, Y., Konda, N., Nonura, H. (1994). Stereoscopic perception in the background of

cyclofusional stimuli. Investigative Ophthalmology & Visual Science, 35(Suppl), 2109.

11. Price, N., Vickers, J., Lee, J., Fells, P. (1987). The diagnosis and surgical management of acquired

bilateral superior oblique palsy. Eye, 1, 78-85.

4


Strabismus In Childhood: Unilateral Cataracts Function Of Age

At Surgery (About 75 Cases)

D. Thouvenin (1, 2), C. Lesage (1), S. Nogue(1), L. Fontes(1), O. Norbert(1),

J.L. Arne(2)

dr.thouvenin@wanadoo.fr

1 : Clinique Saint Nicolas, 55 allées Charles de Fitte 31000 Toulouse France

2 : Service d’Ophtalmologie, CHU Purpan, Place Baylac, 31000 Toulouse cedex France

Abstract

Introduction: We were interested in binocular and oculomotor consequences of unilateral

cataracts (UC) in children, as they provoke an interruption of binocular vision (BV)

development at a more or less sensible stage function of the age of occurrence.

Method: We report 75 cases of UC followed more than 3 years after surgery. 28 cases were

operated on before age 1 year (group1), 22 between 1 and 4 (group2), 25 between 4 and 8

(group3). All had amblyopia treatment.

Results: We describe in each group visual results, oculomotor and BV state, at the latest

exam. Three of the specific signs of infantile strabismus are found in 60% of cases in group1

and none in 84% of older groups. 15 cases (14 in group1) present documented abnormal

retinocortical correspondence, 12 (10 in group3) present normal retinocortical

correspondence, the other cases present profound neutralisation, distributed in all groups. All

types of horizontal deviation are found: essentially esotropia in group1 and microtropias in

others.

Discussion: We observed 2 groups with totally different binocularity. Group1 present typical

“acquired” infantile strabismus syndrome. In older groups, initial development of binocularity

is normal, underlying BV quality increases with age of opacification. Sensorial scars may be

limited to neutralisation. Strabismus is related to the interruption of fusion, but 70% present

microtropias.

Conclusions: Observing unilateral cataracts in children gives unique clinical examples of

dated binocular development arrest and a clinical proof that post natal conditions may lead to

infantile strabismus.

Keywords

Unilateral congenital cataracts. Visual results. Binocular vision. Infantile strabismus.

Introduction

Unilateral congenital cataracts (UCC) have many sensorial consequences: interruption of

monocular visual development which leads to deprivation amblyopia and interruption of

binocular visual development with sensorial and motor disorders.

On a monocular aspect, the brain plasticity period spread over the first decade. The

more precocious, intense and extended the deprivation period, the deeper and more difficult to

treat the amblyopia. This is the usual point of discussion when talking of unilateral cataracts

in children.

On a binocular aspect, the major period of development is limited to the six first months

of life. Early unilateral deprivation disrupts binocular vision (BV) maturation process. The

consequences should be similar to infantile strabismus syndrome. Secondary unilateral

1


deprivation occurs as BV has already matured. Its deterioration should be all the more light

since cataract appears late in the first decade.

Methods

75 cases of unilateral cataracts in children, last exam realised at least 3 years after cataract

surgery (med 6.8 years). We separated the cases in 5 age groups function of age at surgery:

0 to 6 months: 16 cases = group 1

6 months to 1 year: 12 cases = group 2

1 to 2 years: 8 cases = group 3

2 to 4 years: 14 cases = group 4

4 to 8 years: 25 cases = group 5

Surgical procedure, treatment of aphakia and patching procedure are usual and have

been discussed elsewhere, with monocular visual results [1]. We although report monocular

visual results to be more complete on cases description.

We focused the study essentially on binocular state: oculomotricity, state of BV

(Normal or abnormal Retino Cortical Correspondence (nrcc or arcc), neutralisation) and

stereoscopy (Lang stereotest and TNO).

Results

Monocular visual acuity: Fig.1

In group 1 and 2 (surgery before age 1), 40% of the cases gained over 0.4, 40% gained

between 0.1 and 0.4, and 20% stayed below 0.1.

After age 1, 66.8% gained over 0.4, 26.6% gained between 0.1 and 0.4 and 6.6%

stayed below 0.1.

These results are obtained after more than 3 years of amblyopia therapy, medium 6,8

years, and are discussed elsewhere [2].

Visual results in 75 cases of unilateral cataracts in

children

100

80

60

40

20

0

0.4

Surg from 0 to 3 mths (11 cases)

Surg from 1 to 8 yr (45 cases)

Surg from 0 to 1 yr (30 cases)

Fig.1: Visual results function of age at surgery(percentage of cases)

Specific signs of infantile strabismus: Fig.1

Some clinical signs are really specific of infantile strabismus syndrome, the most

primitive state of BV: manifest latent nystagmus, fixation in adduction, dissociated vertical

deviation, asymmetry of optokinetic nystagmus

Three of these signs are found together in more than 75% of cases in group 1, and

60% of cases in group 1 + 2. None of these three signs are found in 84 % of cases of group 3,

4 and 5.

State of Binocular Vision = retino cortical correspondence and neutralisation: Fig.2

48 cases present neutralisation (masking evaluation of RCC), distributed in all groups.

15 cases present proved ARCC, almost all in groups 1 and 2

2


12 cases present documented NRCC, 80% in group 5.

Manifest Latent Nystagmus

DVD

100%

100%

80%

80%

60%

60%

40%

40%

20%

20%

0%

1 2 3 4 5

0%

1 2 3 4 5

% with MLN % without MLN

% with DVD % without DVD

Fig1 : presence or not of MLN and DVD function of age groups at surgery

State of BV

100%

80%

60%

40%

20%

0%

1 2 3 4 5

NRCC ARCC Neutralisation

Fig.2 : State of binocular vision function of age groups at surgery

Stereoscopy improves markedly with age of surgery: Fig.3

No real stereoscopy can be identified on Lang test (and eventually TNO) in groups 1, 2 and 3.

Gross stereoscopy (Lang 500” and TNO > 120”) is found in 3 cases in group 4 and 8 cases in

group 5, and fine stereoscopy in 1 case in group 5 (TNO 60”).

Stereoscopy

100%

80%

60%

40%

20%

0%

1 2 3 4 5

No stereoscopy Depth perception Gross steroscopy Fine stereoscopy

Fig.3: State of stereoscopy function of age at surgery

The type of horizontal deviation presents no specificity: Fig.4

Microtropia is found in 40% of group 1, 2 &3 and 70% of group 4 & 5. The frequency of

esodeviation seems to lessen with age of surgery: 40% in group 1 & 2, 15% over age 1.

Exotropia is found in all age groups around 15%.

3


Horizontal Deviation

100%

80%

60%

40%

20%

0%

1 2 3 4 5

Et > 10 -10 > CT > 10 Xt > 10

Fig.4: Type of horizontal deviation function of age at surgery

Discussion

We can separate two groups with totally different binocularity :

Opacification before age 1 (groups 1 & 2):

We observe a specific binocular anomaly. Binocularity cannot develop itself and definitive

sensorial signs are observed: ARCC, no real stereoscopy. Infantile strabismus syndrome is

observed in 80% of cases in group 1, and 60% in group 1+2. 40% present esotropia, 42%

present microtropia and 18% exotropia. This infantile strabismus syndrome is peculiar. It is

often called “congenital monophtalm syndrome” also observed in other cases of congenital

monocular blindness. It is spontaneously non alternating because of amblyopia but may

become alternating in the specific case of treated monocular congenital cataracts with

amblyopia treatment. It may, in itself limit VA of the sound eye, because of fixation

anomalies (MLN, Fix in Add…) [3]. This last point represents a major reason to cure these

amblyopias. It is possible that vision recovery of the operated eye as tenuous as it may be,

lessen motor anomalies of the sound eye, by balancing visual inputs when fixating in

binocular status.

Opacification after age 1 (groups 3 to 6):

Initial development of binocularity is normal. The later the lens opacification, the better the

underlying BV quality. Sensorial scars may be limited to neutralisation, eventually with

normal underlying binocularity. 70% of groups 4 and 5 have micro or orthotropia, essentially

associated with good monocular visual results. These last cases developed the highest grades

of stereoscopy. « Sensorial strabismus » may appear if deprivation is extended, 10% present

esotropia and 20% exotropia.

Conclusion

Infantile unilateral cataracts lead to a peculiar infantile strabismus syndrome, spontaneously

non alternating that maybe threatful for the vision of the sound eye. This reason must

motivate full treatment of these cataracts. It is an example of « acquired » infantile strabismus,

and a clinical proof that post natal conditions may also lead to this situation.

Later opacified unilateral cataracts appear on a more or less developed BV.

Neutralisation is the most common scar. Normal BV may be recovered in late juvenile

cataracts. Strabismus is related to the interruption of fusion, but 70% of our case present

micro or orthotropia. Exotropia is found in less than 20% of cases in all age groups.

References

1. Thouvenin D., Lesueur L., Arne J.L.(1995). Intercapsular lens implantation in pediatric aphakia : study of 87

cases compared to 88 cases without lens implantation.. J Fr Ophtalmol, 18 (11), 678-687.

2. Thouvenin D., Nogue S., Fontes L., Arne JL. (2003). Long term functional results of the treatment of

unilateral congenital cataracts with early surgery. About 20 cases. J Fr Ophtalmol, 26 (6), 562-569.

3. Thouvenin D., Taurines E., Noblet P. (2000). Oculomotor Status in Treated Monocular Congenital Cataracts.

In De Faber (Ed.), Trans 26 th meeting ESA. (pp 44-50). Swets and Zeitlinger: Lisse.

4


The Use Of A Computerised System For The Study Of Binocular

Vision: First Experiences

Hector Rojas-Anaya a-b , Joy White a , Lionel Ripley b

a Sussex Eye Hospital, Orthoptic Department

Eastern Road, Brighton BN2 5BF, United Kingdom

joy.white@bsuh.nhs.uk

b University of Sussex, Department of Engineering and Design

Falmer, Brighton BN1 9QT, United Kingdom

h.rojas@sussex.ac.uk

Abstract

A computerised system is described, which takes advantage of information-technology

techniques and the availability of affordable multimedia hardware to provide subjective tests

for the clinical assessment of binocular vision. Six basic orthoptic tests were implemented:

dissociated phoria, AC/A ratio, Hess screen, fusion, aniseikonia and stereoacuity. Results

from the dissociated phoria test are discussed in this article, showing that the system

constitutes a robust platform on which clinical research can be performed, providing a

powerful and versatile means of presenting dichoptic visual stimuli and collecting and

analysing psychophysical data. Lessons learned with this prototype will permit further clinical

investigations on the performance of the human visual system that may suggest novel ways of

assessing binocular vision function.

Keywords

Binocular vision, psychophysics, dichoptic stimuli, phoria, computerised tests.

Introduction

The last three decades have seen an enormous amount of research on vision in a range of

disciplines: biomedical engineering, experimental psychology, neurophysiology, cognitive

sciences and other related areas. Most of the research related to binocular vision has been

carried out using expensive dedicated computerised systems due to the requirement of

presenting accurate dichoptic stimuli. Although this research has produced much valuable

knowledge about binocular vision function, not enough of this knowledge has been

transferred to the consulting room because of practical and financial limitations. A major

contribution of computerised systems to the study of binocular vision is the use of dynamic

stimuli to study temporal properties of the visual system, which have traditionally been

implemented using graphics-system microprocessors to enhance the speed of images

manipulation and assembly language to provide real-time generation of the patterns and exact

timing (1). With the advent of the personal computer (PC) and its widespread use throughout

the 1980s, there was a growing interest in the design of PC based tests for orthoptic diagnostic

and therapeutic procedures, resulting in several dozen commercial and freeware systems with

several advantages over their microprocessor-based counterparts (2). Recent examples of this

kind of PC based systems are the Test Chart 2000 (3) and the I-Bit (4). Current advances in

information technology and computer graphics make it now possible to apply techniques from

the binocular-vision research domain to the diagnosis and treatment of patients with

binocular-vision abnormalities thanks to the fact that multimedia hardware and, increasingly,

computer power are now available at affordable prices for extended clinical use. The system

1


described in this article was designed to explore this possibility with the future aim of finding

new testing paradigms for clinical binocular vision.

Material and Methods

Subjects viewed dichoptic targets on a flat-screen computer monitor (Iiyama Vision Master

Pro 453 ® ) by looking through a pair of LCD shutter-glasses (Stereographics Crystal Eyes ® )

at a fixed viewing distance of 330 mm with the head positioned on a chin-rest. The monitor

had a resolution of 1024x768 pixels driven by a stereo-ready graphics card (3Dlabs GVX1 ® )

which also provided synchrony with the LCD shutter-glasses through an infrared emitter

(Stereographics ENT3 ® ), at a vertical refresh rate of 120 Hz, such that each eye saw images

at 60 Hz. The display view port was 360 x 270 mm, with 1 pixel subtending 3.6 min arc.

Observers sat in a room with low levels of ambient illumination provided by natural light. The

mean luminance of the screen, as measured through a shutter lens, was 6.0 cd/m 2 . The patient

response to the stimuli was detected using the keyboard, the mouse or a game pad. A block

diagram and images of the system are presented in Fig. 1 and Fig. 2. The main program is

written in Visual C/C++ ® , the visual stimuli and the LCD glasses interface are programmed

in OpenGL ® and the data from the different tests are sent to a computation engine written in

Matlab ® for psychophysical analysis and presentation of results.

Fig. 1. Block diagram of the system Fig. 2. Images of the system

Twenty subjects took part in the experiments to evaluate the dissociated phoria test.

The sample comprised members of staff at the Sussex Eye Hospital. All had Snellen visual

acuity of 6/6 or better. Corrective spectacles were worn when necessary. The research

followed the ‘Code of Ethics of the World Medical Association’ (Declaration of Helsinki).

Two targets subtending 3 x 3 degrees are presented dichoptically at the display origin,

which position is calibrated by the operator to be at the subject’s eye level on the median

plane. There are two symbols located centrally on one of the targets, which are aligned

vertically and change randomly over time: sometimes there are two similar symbols and

sometimes there are two dissimilar symbols. Each symbol subtends 11 x 11 min arc, with a

gap of 7.3 min arc between them. For the measurement of dissociated phoria, the subject

under test performs two tasks simultaneously while the dichoptic targets are on the screen.

The first task is to constantly superimpose the targets, which drift away from each other. This

task determines the phoria measurements. The second task is to press a game-pad button

every time the two tattoos are the same, receiving audible feedback for correct answers. This

task is used to control accommodation.

A geometry consistent with the model of the binoculus or theoretical median eye is

employed (5). In this case there is a single set of visual directions related to the position of the

head, head-centrally rather than oculo-centrally (6). This geometry allows the measurement of

phoria to be independent of the subject’s interpupillary distance. The main program collects

the raw data, which consist of samples of horizontal and vertical differences in pixels between

the dichoptic targets, together with the time in seconds of each sample from the start of the

2


test. The main program also monitors performance of the symbol-pair accommodation task,

sending a ‘successful test’ message if the task was carried out properly, or a warning if the hit

rate is less than 75% or if the false-alarm rate is greater than 25%, which are indicators of

poor accommodation, helping the operator decide if the data collected should be retained or

discarded. The raw data are sent to the computation engine, which plots the change of

horizontal and vertical phoria during 70 s of eye dissociation, calculates the phoria values in

prism dioptres and displays the final results in the output window, shown in Fig. 3.

Fig. 3. Output window of the dissociated phoria test

Results

Repeatability was assessed using SPSS ® and following the ‘within-subject standard deviation

(sw)’ method (7), which consists of obtaining the common standard deviation of repeated

measurements (sw) and calculating a repeatability coefficient from it, as defined by standard

BS5497, part 1, of the British Standards Institution (8). A sample of m=20 repeated phoria

measurements on each of n=8 subjects was used giving a repeatability coefficient of 2.0 Δ.

The tests were carried out randomly throughout a period of 40 days, with at least a two-hour

rest between consecutive tests if carried out in the same day and with no more than three tests

per day per subject.

Agreement between the computerised and clinical test was assessed using the 95%

limits of agreement method of Bland and Altman, as an alternative to the use of the

correlation coefficient which they show may be misleading for this purpose (9). One

measurement was made with the computerised phoria test and one with the objective

alternating prism cover test (clinical test) for each of the 20 subjects, in random order. All

clinical measurements were made by the same qualified orthoptist. A single reading by both

methods was taken, without repeating suspect readings. Results show 95% limits of

agreement of ±2.7 Δ.

Discussion

The repeatability coefficient indicates that the difference between two measurements for the

same subject is expected to be less than 2.0 Δ, which is acceptable, considering that phoria

cannot be measured with high precision because of the number and variety of neural factors

which cannot be eliminated and which are constantly changing (10). The 95% limits of

agreement of ±2.7∆ suggest that a phoria measurement by the computerised method would be

between 2.7 ∆ less and 2.7 ∆ greater than a measurement by the prism cover test, which is

considered as good agreement because the prism cover test is limited by the smallest deviation

of an eye that a clinician can detect, which, on average, is about 2 Δ (11). Also, Daum (12)

has suggested that lateral phoria measurements by the prism cover test are accurate within 3 Δ

to 5 Δ. Moreover, a review of the literature by Schroeder et. al (13), regarding comparisons

3


among methods of measuring dissociated phoria, found that they differ in the technique used

for dissociation, in the ability to control accommodation, in the level of proximal convergence

induced, or in the method by which phoria is quantified. These differences amongst methods

justify the limits of agreement found.

The above results show that the system measures changes of horizontal and vertical

phorias over time accurately, has good repeatability and correlates well with its clinical

counterpart. The main advantages of the proposed phoria test over traditional methods are

better accommodation control, a more attractive test for children, and more importantly, the

possibility of tracking and plotting phoria changes over time. This last characteristic is

currently being explored and it opens a new field of research. A disadvantage of the use of

LCD shutter-glasses for eye dissociation is the presence of crosstalk when viewing peripheral

dichoptic targets. In conclusion the system described constitutes a robust platform on which

clinical research can be performed, providing a powerful and versatile means of presenting

dichoptic visual stimuli and collecting and analysing psychophysical data over time.

Acknowledgements

Most of the research related to this paper was supported by the Mexican National Council for

Science and Technology (CONACYT). Special thanks to the staff of the Orthoptic

Department of the Sussex Eye Hospital, Brighton, England, for the enormous help provided

regarding practical and clinical issues during this project.

References

1. Obaidat, M. S., Abu-Saymeh, D. (1999). A real-time video pattern generator for use in Ophthalmology.

Journal of Medical Engineering & Technology 23(4), 135-143.

2. Maino, D.M., Maino J.H. (1989). Computer Applications in Optometry. Boston: Butterworths.

3. Thomson, W. D. (2002). Test Chart 2000. Retrieved 13 October, 2002, from http://www.thomson-softwaresolutions.com

4. Nottingham Technology Ventures (2004). Interactive binocular treatment (I-BiT). Retrieved 18 August,

2004, from http://www.nottinghamtechnologyventures.com/healthcare_op.htm

5. Ono, H. (1991). Binocular visual directions of an object when seen as single or double. Vision and visual

dysfunction, (9), 1-18.

6. Howard, I. P., Rogers, B. J. (2002). Seeing in depth. Ontario: I. Porteous.

7. Bland, J.M., Altman, D.G., (1996). Statistic notes: measurement error and correlation coefficients. British

Medical Journal, 313, 41-42.

8. British Standards Institution (1979). Precision of tests methods I: Guide for the determination and

reproducibility for a standard test method (BS5497, part 1). London: British Standards Institution.

9. Bland, J.M., Altman, D.G. (1986). Statistical methods for assessing agreement between two methods of

clinical measurement. Lancet, i, 307-310.

10. Ogle, K. N. (1964). Researches in binocular vision. New York: Hafner Publishing Company.

11. Romano, P.E., van Noorden, G. K. (1971). Limitations of cover test in detecting strabismus. American

Journal of Ophthalmology, 72, 10-12.

12. Daum, K.M. (1991). Heterophoria and heterotropia. In: J.B. Eskridge, J.F. Amos, J.D. Bartlett (Eds.) Clinical

Procedures in Optometry. (pp 72-90). Philadelphia, PA : Lippincott.

13. Schroeder, T.L., Rainey, B.B., Goss, D.A., Grosvenor, T.P., (1996). Reliability of and comparisons among

methods of measuring dissociated phoria. Optometry and Vision Science. 73(6), 389-397.

4


Abstract

Disruption of Binocular Vision following Cataract Surgery.

Joy White

Orthoptic Department, Sussex Eye Hospital, Eastern Road, Brighton BN2 5BF,UK

joy.white@bsuh.nhs.uk

The aim of this study was to assess the incidence of disruption of binocular vision following

cataract surgery and to re-evaluate the role of Orthoptists in pre-assessment clinics for

cataract surgery.

A retrospective study was carried out of all patients who attended the hospital for cataract

surgery between January 2003 and December 2003. The incidence of ocular motility disorders

and diplopia which had been recorded in the case notes was noted pre-operatively, two

weeks post operatively and if it was still persisting more than six weeks post operatively. All

patients with persistent diplopia/symptoms related to disruption of binocular vision had been

referred for Orthoptic assessment.

In the period from January-December 2003 2147 patients had cataract surgery, 93% of whom

had surgery under local anaesthesia. There was a total of 17 (0.8%) cases with persistent

disruption of binocular vision post cataract surgery. The aetiology of the binocular problems

was divided into three groups 1) refractive, 2) pre-existing deviation and 3) induced deviation.

Treatment was by means of prisms, refractive correction, occlusion, Botulinum toxin and

surgery.

The incidence of disruption of binocular vision in those patients undergoing cataract surgery is

not high. However the symptoms that they have can be very difficult for the Orthoptist to

eliminate despite a range of treatment modalities. The Orthoptist therefore has an important

role in pre-assessment cataract surgery clinics in highlighting those patients in which there are

potential binocular complications.

Keywords

Cataract, diplopia

Introduction

The incidence of binocular complications has been well documented. The aim of this paper

was to assess the incidence of these complications and to re-evaluate the role of Orthoptists in

pre-assessment clinics for cataract surgery. Orthoptists in the UK have an increasing role in

cataract clinics, carrying out ophthalmic assessments to include biometry both pre-op and

post-operatively. The same patients seen in the Cataract clinics may then attend the

Orthoptic clinics with binocular complications.

Methods


A retrospective study was carried out of all patients attending for cataract surgery at the

Sussex Eye Hospital from January 2003 until the end of December 2003. The case notes were

reviewed to ascertain whether there was any documented ocular motility disorder or diplopia

pre-operatively, and also whether surgery had been cancelled for any of these reasons. It was

then noted whether the patients had any binocular complaints at two weeks post-op and

persisted at six weeks post-op. The aetiology of the disruption of binocular vision was

ascertained where possible and any treatment recorded.

The type of cataract surgery carried out was noted and whether it was carried out

under local or general anaesthetic. Any complications at the time of surgery were also noted.

Results

A total of 2147 cataract operations were carried out in the period from January to December

2003. The procedure was carried out under local anaesthetic in 93% of cases.

Pre-operatively ? cases had been noted to have a pre-existing condition which may

give rise to binocular complications but in no case was surgery cancelled.

Discussion

Orthoptists should be seen to take a pro-active role to ensure that the binocular complications

that are experienced by patients are minimised, and excluded where avoidable.

Acknowledgements

The Consultant Ophthalmologists of the Sussex Eye Hospital for allowing me to report on

their patients.

References

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