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Vidhya Subramanian, Reed M. Jost, Yi-Zhong Wang, Eileen E. Birch; Quantification of Suppression in Strabismic and Anisometropic Amblyopia. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6339.
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While the dominant theory is that amblyopia develops as a result of suppression, this hypothesis has not been directly tested in amblyopic children. We aimed to determine whether suppression is associated with amblyopia and set out to quantify the severity of suppression, separately for strabismic vs. anisometropic children.
8 amblyopic children (4 strabismic; 4 anisometropic) and 20 normal controls ages 6-15 years participated. A coherent motion threshold (% coherence) was measured using video gaming goggles, which allowed dichoptic presentation; One eye viewed coherent motion (dots moving up or down), and the other eye viewed noise (pseudorandom motion dots). The contrast of the dots in the amblyopic eye (AE) was always 100%; contrast in the fellow eye (FE) was set to 100%, 80%, 60%, 40% or 20%. Thus, dichoptic motion coherence threshold was obtained for contrast ratios (AE/FE) = 1.0, 1.25, 1.67, 2.5, and 5.0. The contrast ratio which allowed the child to experience binocular combination of signals presented to the amblyopic and fellow eyes, was used to quantify the strength of suppression. We also calculated a second index of strength of suppression, the dichoptic motion coherence threshold ratio (AE threshold/FE threshold) at contrast ratio = 1.0 (same contrast presented to both eyes).
Amblyopic children required a contrast ratio ≥ 5.0 to reach a dichoptic threshold ratio close to 1 (mean = 1.27). Amblyopic children showed severe suppression, with a mean dichoptic threshold ratio of 4.1 at contrast ratio of 1, significantly higher than normal control children (1.3; Mann-Whitney U = 18; p < 0.001). Interestingly, children with strabismic amblyopia had a mean dichoptic threshold ratio that was approximately 4X greater than children with anisometropic amblyopia (10.8 vs 2.6). Severity of suppression was not correlated with depth of amblyopia (p>0.10).
In this study we were able to demonstrate the presence of suppression and residual binocular interaction in amblyopic children. More importantly, our results indicate that the severity of suppression is associated with etiology of amblyopia but may not be associated with depth of amblyopia.
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