‘Global Perspectives Converge Downunder’
Transactions of the Xth International Orthoptic Congress
14-17 November 2004
Edited by: D.Verlohr, Z.Georgievski, A.Rydberg
and t Institution of Engineers, Australia.
Table of Contents
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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
Ophthalmic Technology & Vision Science
Professional Development & Education
Public Health Agenda & Screening
Strabismus - Concomitant
Strabismus - Incomitant
Symposia - AAPOS: Childhood Blindness Worldwide
- ISA: Update on Chemical (or Pharmacological) Treatment
- Vision Screening: Critical Appraisal of the Evidence in
Favour (or not...!) of Vision Screening in Children
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Oral presentations in black
Posters in blue
‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress
Factors Contributing to the Outcome of Sensory Testing in Patients with Anomalous Binocular Correspondence — Kyle
‘Global Perspectives Converge Downunder’- Xth International Orthoptic Congress
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
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
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,
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
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
Range of Accommodation and Binocular Vision after Refractive Surgery — Jeroen Claeys, D.Godts, R.Trau,
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
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.
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
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.
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
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-
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
At 33 cm
Only 25 (34%) 3 (4%) 22 (30%) 12 ± 2Δ
Only 1 (1%) 5 (7%) 10 (14%) 30 ± 3Δ
Retinal Elements 7 (9%) 2 (3%) 4(5%) 18 ± 2Δ
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).
Fig. 1 Magnitude and Direction of Strabismus vs. Pattern of Rewiring in Patients with ARC
Fovea of deviating eye
-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
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
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 <
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
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
Time in months
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).
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
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
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.
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.
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Science. 35: 4168-4179.
Range of accommodation and binocular vision after refractive
Jeroen Claeys, Daisy Godts, Ren Trau, Marie-Jos Tassignon
University Hospital Antwerp, Department of Ophthalmology
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
Conclusion: In our study refractive surgery does not alter binocular vision and ocular motility.
Accommodation may change in a number of patients.
Binocular vision, accommodation, refractive surgery, orthoptics, LASEK.
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
accommodation and convergence were measured with the R.A.F. near point rule, using pushup
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).
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.
Patient Preoperative refractive error Postoperative refractive error Preoperative
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
values -1.92 -1.97
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
-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
values -7.63 -7.06
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
values +2.06 +2.06
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.
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
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
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
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.
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
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
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
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
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
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.
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-
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-
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.
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
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
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
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
Ocular dominance, Monovision correction
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
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?
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. 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.
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.
Right Left Alternating
Right Left Alternating
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.
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
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
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:
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.
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
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.
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
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-
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-
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.
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
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.
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.
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.
Michael Port and Andy Ham for apparatus construction. Robin Farr for help with figures.
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.
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.
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
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.
Sensory ocular dominance, Binocular rivalry, Exclusive perceptual dominance, Visual evoked
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
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
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.
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).
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
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.
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.
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.
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.
The Age-Related Decline in Stereopsis as Measured by Different
Louise Garnham and John Sloper
Moorfields Eye Hospital
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.
Stereoacuity; TNO, Titmus, Frisby and Frisby-Davis stereotests
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
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
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:
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
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,
c Department of Ophthalmology, School of Medicine, Kitasato University,
1-15-1 Kitasato, Sagamihara, Kanagawa, 228-8555 Japan.
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
Ocular dominance, Binocular rivalry, Sensory eye dominance, Balance technique,
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
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
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
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.
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
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.
This study was supported in part by Grant from the Ministry of Education, Science, Sports,
Culture, and Technology, Japan (No.14571686)
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
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.
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
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.
Visual acuity, stereoacuity, Titmus stereo tests, Lang stereotest.
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)
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.
Table 1. Number .of subjects
with decreased VA
Decimal Log M
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
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
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
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
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
The results of the circle test in the Titmus
The results of the Animal test in the Titmus
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
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.
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),
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
Stereoacuity Following Unilateral And Bilateral Cataract
Rebekah Lawry, Susie Sarangapani, Sheriden Graham, Mandeep Sagoo,
Carolyn Calcutt, Veronica Ferguson, Raj Maini.
Charing Cross Hospital, Fulham Palace Road, London W6 8RF. UK
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
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
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
Visual acuity, stereoacuity, near, distance, anisometropia
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
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?
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
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.
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-
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
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.
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.
Appreciation to ‘Joe’ C. Danchaivijitr for compiling the statistics.
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;
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
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 email@example.com
Visual skills, prevalence, accommodative facility, vergence, binocular vision
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.
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
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.
Fig 1: Refractive Errors
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
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)
Fig 3B: Vergence (Base In)
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)
No. of Students
Criteria for visual skills and Number of students classified as “weak”
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
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.
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.
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.
Diagnosis And Treatment In Patients With Asthenopic Symptoms
Due To Exophoria
Department of Clinical Neuro Sciences
S:t Eriks Ögonsjukhus
SE-112 82 Stockholm
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.
Asthenopia, prism glasses, operation, resection, recession.
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  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 .
Asthenopia is thought to represent disturbances in the sensory- motor system . Such
anomalies may be a heterophoria, disturbed function of the extraocular muscles or poorly
corrected refractive errors including anseikonia . Asthenopic symptoms may appear when
compensation-mechanisms for these anomalies become insufficient.
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
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
Statistical differences were tested with Wilcoxon Signed Ranks Test and analysis of
variance (General Linear Model).
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
Satisfied Part satisfied Not satisfied
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
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  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
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.
Thanks to the orthoptists in the clinic who helped us with orthoptic investigations.
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-
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,
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,
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.
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
of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara ,Tochigi, 324-8501 Japan
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.
Monovision, IOL, Visual acuity, Binocular function, Satisfaction
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.
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.
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
77.4% of patients satisfied monovision. The rate of using glasses was 15.5%.
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
This study was supported in part by Grant from the Ministry of Education, Science, Sports,
Culture, and Technology, Japan (T. Niida; No.14571686).
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.
Fig.3. Stereoacuity measured by Titmus stereo tests at 40 cm.
Fig.4. Fusional amplitude measured by major amblyoscope.
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
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.
torsion, cyclotropia, fusional vergence, stereopsis, binocular single vision.
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)
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.
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).
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.
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
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 .
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 .
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,
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,
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-
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.
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),
1 : Clinique Saint Nicolas, 55 allées Charles de Fitte 31000 Toulouse France
2 : Service d’Ophtalmologie, CHU Purpan, Place Baylac, 31000 Toulouse cedex France
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
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
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
Unilateral congenital cataracts. Visual results. Binocular vision. Infantile strabismus.
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
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
deprivation occurs as BV has already matured. Its deterioration should be all the more light
since cataract appears late in the first decade.
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 . 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).
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 .
Visual results in 75 cases of unilateral cataracts in
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
12 cases present documented NRCC, 80% in group 5.
Manifest Latent Nystagmus
1 2 3 4 5
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
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”).
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%.
1 2 3 4 5
Et > 10 -10 > CT > 10 Xt > 10
Fig.4: Type of horizontal deviation function of age at surgery
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…) . 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
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.
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.
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.
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
b University of Sussex, Department of Engineering and Design
Falmer, Brighton BN1 9QT, United Kingdom
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.
Binocular vision, psychophysics, dichoptic stimuli, phoria, computerised tests.
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
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
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
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.
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
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.
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.
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2004, from http://www.nottinghamtechnologyventures.com/healthcare_op.htm
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dysfunction, (9), 1-18.
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reproducibility for a standard test method (BS5497, part 1). London: British Standards Institution.
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clinical measurement. Lancet, i, 307-310.
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11. Romano, P.E., van Noorden, G. K. (1971). Limitations of cover test in detecting strabismus. American
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Disruption of Binocular Vision following Cataract Surgery.
Orthoptic Department, Sussex Eye Hospital, Eastern Road, Brighton BN2 5BF,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
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
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.
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.
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.
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.
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.
The Consultant Ophthalmologists of the Sussex Eye Hospital for allowing me to report on