Assessment of vision and amblyopia by preferential looking tests after early surgery for unilateral congenital cataracts.

Preferential looking tests obtained over the first 3 years were used to evaluate the development of visual acuity of 21 patients who underwent surgery for unilateral congenital cataracts and fitting of contact lenses before age 6 months. Mean acuity of the aphakic eyes improved rapidly in the first year; however, between the end of the first year and the end of the third year there was no improvement in mean aphakic acuity. Consistent with this, the percentage of patients who were amblyopic by the criterion interocular difference in acuity (IOD) of 0.5 octaves (oct) or greater was 94% at the first test age near the onset of occlusion therapy, decreased to 72% at the end of year 1, and increased to 89% by the end of year 3. Variations in occlusion therapy appear to account for these results: mean hours of occlusion per day were 6.2 in year 1, 4.4 in year 2, and 2.7 hours in year 3. Furthermore, the IOD at age 1 year was negatively correlated with hours of occlusion in the first year and the IOD at age 3 years was negatively correlated with cumulated hours of occlusion over all 3 years. That is, the less the amount of occlusion therapy, the greater the IOD. The patients' ages at time of surgery did not account for any further variance in these results than that accounted for by occlusion therapy. This study demonstrates that PL acuity measurement can aid in monitoring the response to occlusion therapy of infants with deprivation amblyopia due to unilateral congenital cataracts.