Purpose: Dense congenital unilateral cataracts may compromise visual development through visual deprivation and biased interocular competition, whereas dense congenital bilateral cataracts compromise visual development primarily through visual deprivation alone. Differences in sensory deficits between the two patient groups with these disorders may reflect the specific effects of unequal competition. To determine whether early treatment (at <8 weeks of age) minimizes the adverse effects of unequal competition, grating acuity deficits during the immediate posttreatment period and contrast sensitivity deficits at 6 to 8 years of age were assessed in 29 children with histories of dense congenital unilateral or bilateral cataracts who had had treatment between 1 and 8 weeks or 12 and 30 weeks. All children maintained good to excellent compliance with optical correction and occlusion therapy.
Methods: Grating acuity was measured using a two-alternative forced-choice preferential-looking staircase protocol. Contrast thresholds at three spatial frequencies (0.38, 1.5, and 6 cyc/deg) were measured at each of two temporal frequencies (2- and 8-Hz sinusoidal counterphase modulation) using D6 grating patches.
Results: Grating acuity deficits in the immediate posttreatment period were similar in patients with a history of unilateral cataract (n=10) and those with a history of bilateral cataracts (n=6) when treatment was provided during the first 8 weeks of life. With later treatment, patients with a history of unilateral cataract (n=7) had significantly larger grating acuity deficits than patients with a history of bilateral cataracts (n=6). Children with a history of dense congenital unilateral cataract had similar deficits in contrast sensitivity to children with a history of bilateral cataracts when treatment was initiated during the first 8 weeks of life. When treatment was initiated later (i.e., at 12-30 weeks), patients with a history of unilateral cataract showed greater deficits in contrast sensitivity and a dependence of the amount of spatial contrast sensitivity deficit on temporal frequency than did patients with a history of bilateral cataracts.
Conclusions: These findings support the hypothesis that only visual deprivation is active as an amblyogenic factor during the first weeks of life, but when unilateral deprivation is prolonged to 12 to 30 weeks, unequal competition also plays a role in amblyogenesis.