Contrast sensitivity in amblyopia. III. Effect of occlusion.

Contrast sensitivity of 26 children (mean age 9 years) was measured using vertical gratings during the course of pleoptic treatment. A statistically highly significant improvement in the vision of amblyopic eyes occurred during intensive treatment in the hospital. Occlusion of the amblyopic eye (inverse occlusion) before the pleoptic treatment did not effect the function of the amblyopic eyes. During 8-week occlusion of the dominant eye (direct occlusion) after pleoptic treatment changes in the vision of the amblyopic eyes were statistically insignificant. In some patients there was change in contrast sensitivity without a corresponding change in visual acuity. The contrast sensitivity of the dominant eye decreased markedly during occlusion in 12 patients. After a continuous occlusion of only 2 weeks there was a statistically significant decrease at spatial frequency 6 c/deg. There was no simultaneous decrease of visual acuity; thus the change can be called 'hidden occlusion amblyopia'. An additional 8-week occlusion did not cause any statistically significant decrease in contrast sensitivity, but visual acuity of 2 patients decreased slightly, a sign of beginning occlusion amblyopia. The changes disappeared during 'Einschleich'-occlusion or penalization except in one child whose previously dominant eye became non-dominant and slightly amblyopic.