Transactions from the Xth International Orthoptics Congress 2004

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Fig. 1 Magnitude and Direction of Strabismus vs. Pattern of Rewiring in Patients with ARC Temporal Retina Nasal Retina Fovea of deviating eye Optic Disc -30 -20 -10 +10 +20 +30 Only deviation point rewired Only fovea rewired Both points rewired Only those deviations between XT 15 and ET 20 are compatible with a pseudo-fovea. Nasal retina, and the corresponding areas in the visual cortex, appears capable of acquiring fusion with the non-corresponding point in the dominant eye over a wider range of deviations than temporal retina. The deviating fovea is more likely to “rewire” in large angles of strabismus. Mean visual acuity in the dominant eye was .9 ± .02 (20/22 or 6/7), compared to .7 ± .04 (20/30 or 6/9) in the deviating eye. This is statistically different (p < .001). Amblyopia was found in 44% of cases. Visual acuity appears to have no effect on the pattern of rewiring. Specifically, decreased acuity is not associated with rewiring of the fovea of the deviating eye (p > .3). ARC is more common in esotropia, than in exotropia or hypertropia. Seventy-four percent of the study patients were esotropic, 19% exotropic, and only 7% hypertropic. The mean angle of strabismus for esotropic patients was 19 ± Fig. 2 Direction of Deviation vs. Pattern of Rewiring % of Patients 80 70 60 50 40 30 20 10 0 Pseudofovea Rewired Fovea ET XT Esotropes were more likely to acquire a pseudofovea, while exotropes were more likely to rewire the deviating fovea (p .5), esotropes and exotropes developed different patterns of ARC. Fig. 2 illustrates that esotropes are more likely to acquire a pseudo-fovea than to rewire the deviating fovea. The exotropic patient was as likely to develop a pseudo-fovea as to rewire the fovea. Exotropes are significantly more likely to rewire the fovea than esotropes (p < .005). All study patients had onset of strabismus during the first 10 years of life. The oldest age at onset of a new strabismus that resulted in ARC was 6 years. This esotropic patient rewired both retinal elements on both tests within 8 months of onset of the strabismus. The oldest age at which ARC was noted for the first time in a patient with longstanding strabismus was 15 years of age. This patient first had surgery for a large angle infantile esotropia at age 12 years. In the years prior to surgery, she repeatedly demonstrated dense alternating suppression on all sensory tests. Within 4
three years of surgical alignment, she began to report a pseudo-fovea on the Bagolini Test. The oldest age at which a pre-existing ARC modified to adapt to a new deviation following strabismus surgery was 17 years (2 patients). ARC was confirmed at a younger age in both Fig. 3 Magnitude of Exodeviation vs. Time to ARC Response 30 Time in months 25 20 15 10 5 0 0 10 20 30 40 50 Exotropia in prism diopters The larger the angle of exotropia, the longer it takes to develop ARC (r = .81). cases, and a new anomalous correspondence developed within 3 months of surgery. For the group as a whole, the mean length of time needed to rewire a pre-existing ARC following a change in the deviation was 7.7 ± 1 months (range 2 – 24 months). There was no correlation between the age of the patient at the time of surgical alteration in the strabismic angle and the length of time needed to adjust the ARC to the new angle (r = .01). Mean time needed to rewire was more closely correlated with magnitude and direction of strabismus. Esotropic deviations took an average of 6.3 ± 1 months to adapt, while exotropic deviations required a mean 15.5 ± 3 months. This difference is significant (p < .0025). There was a weak positive correlation between the magnitude of esotropia and time to new correspondence (r = .31), but a very strong positive correlation between the severity of exotropia and time needed to rewire (r = .81) (Fig. 3). Patients tended to demonstrate evidence of ARC on Bagolini glasses after a mean 7 ± 2 months, compared to 12 ± 2 months for the Worth 4-dot (p < .01). The mean time needed to rewire the point of deviation was 6 ± 1 months, while it took an average of 10 ± 2 months to rewire the fovea, regardless of test used (p < .05). The disparity in time needed to rewire the fovea is more pronounced on the Worth test than the Bagolini (p < .02). Discussion This study compared one mildly dissociating test and one highly dissociating test of retinal correspondence to evaluate the subjective visual direction of both the deviation point and the fovea of the deviating eye. Results provide clear evidence in support of earlier studies concluding that the greater the similarity of the images received by the two eyes, the easier it is for the visual system to achieve anomalous fusion. In this study, subjects were more likely to demonstrate an ARC response, and to do so after a significantly shorter period of time, on the minimally dissociating tests. However, the 7% who exhibited ARC on the Worth 4 dot, and not on the Bagolini test, clearly defy the classic teaching on the effect of dissimilar retinal images on fusion ability. A previous study has also shown that, contrary to traditional thought, it is possible to show ARC on a highly dissociating test, without expressing ARC on a minimally dissociating test.(3) It appears then, that dissociation is not the only factor that determines sensory test results. According to this study, the other variables that appear to impact the outcome include: (a) retinal element evaluated (fovea vs. deviation point), (b) magnitude of the deviation, (c) direction of the deviation (ET vs. XT), and (d) age of onset of the strabismus. Retinal Element Evaluated. It has been thought that all retinal elements of the strabismic eye between the deviation point and the fovea simultaneously rewire to correspond with the fixating eye.(1) If this were the case, testing the directional value of any single point within that range, or detecting fusion in the presence of a manifest strabismus, would be sufficient to prove 5
Page 1 and 2: ‘Global Perspectives Converge Dow
Page 9 and 10: The Burian Memorial Lecture: Factor
Page 11: Results Seventy-four patients fulfi
Page 15 and 16: onto temporal retina, regardless of
Page 17 and 18: Range of accommodation and binocula
Page 19 and 20: Table 2 Patient Preoperative fusion
Page 21 and 22: Assessing The Dominant Eye: A New M
Page 23 and 24: Figure 1. The Sensory Dominance Tes
Page 25 and 26: Does Dissociation Reduce Stereoacui
Page 27 and 28: Methods Observers were students in
Page 29 and 30: Initial 1.2 ** 1.4 ** 6.4 **** 7.1
Page 31 and 32: Does stereoacuity correlate with in
Page 33 and 34: Results The distance and near stere
Page 35 and 36: 3. Frisby, J.P., Davis, H., Edgar,
Page 37 and 38: measurement of sensory dominance (3
Page 39 and 40: Fig. 1. Durations of exclusive perc
Page 41 and 42: The results of all four stereotests
Page 43 and 44: varied, from 100% to 80% to 60% to
Page 45 and 46: Can stereo tests be an indicator of
Page 47 and 48: Pass No. Table 1. Number .of subjec
Page 49 and 50: Stereoacuity Following Unilateral A
Page 51 and 52: Table 1 Pre-operatively Post-operat
Page 53 and 54: Measurement And Improvement Of Visu
Page 55 and 56: Table 1 Criteria for visual skills
Page 57 and 58: Diagnosis And Treatment In Patients
Page 59 and 60: Reduction of asthenopic symptoms -
Page 61 and 62: Monovision By Implanted Intraocular
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Acknowledgements This study was sup
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The Effect Of Simulated Torsional D
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Table 3. Mean fusional convergence
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Strabismus In Childhood: Unilateral
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12 cases present documented NRCC, 8
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The Use Of A Computerised System Fo
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test. The main program also monitor
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Abstract Disruption of Binocular Vi
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Transactions from the Xth International Orthoptics Congress 2004

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