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T Ma-Naim, U Polat, Y Bonneh, D Sagi; Normal Contrast Summation Between Eyes In Amblyopia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3936.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To explore contrast summation between the eyes in amblyopia. Methods: Contrast detection thresholds (temporal 2AFC, 160 ms each presentation) were measured for each eye, amblyopic and non-amblyopic, and both, for vertical Gabor targets (1.5-6 cpd; λ=σ) in isolation and in the presence of laterally placed (4λ from target) collinear Gabor flankers (C=5*Cthreshold) of the same spatial-frequency. For binocular measurements the contrasts presented to the amblyopic eyes were either factorized (to compensate for reduced sensitivity) or not. 62 amblyopic and 16 normal sighted observers were sampled. Results: Thresholds for the amblyopic eyes were higher, as compared with the non-amblyopic eyes, by a factor of 3.3 (SE=0.35) for isolated targets and 4.05 (SE=0.52) with flankers present. The presence of flankers had no significant effect on thresholds in the amblyopic eye (4% improvement) but significantly improved thresholds in the non-amblyopic eye of amblyopes by 27%, and in the normal-sighted observers by 61%. This difference reflects reduced lateral facilitation in the amblyopic eyes. Binocular thresholds in amblyopes were similar to thresholds in the non-amblyopic eye, showing a binocular/monocular ratio of 0.9 (SE=0.13), not significantly different from unity, as compared with 0.69 (SE=0.04) in normals. When the target contrast presented to the weaker eye was increased to compensate for the reduced sensitivity, binocular thresholds showed strong summation between the eyes and were 0.65 (SE=0.024) of the monocular thresholds in amblyopes, and 0.61 (SE=0.06) in normals. No significant differences were found between the different amblyopia types. Conclusion: Despite having abnormal spatial integration, contrast summation across eyes in amblyopia is as efficient as in normal sighted observers when monocular inputs are compensated for sensitivity loss. This result holds in the presence and absence of high contrast flankers.
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