Further observation was made of 100 cases of occlusion amblyopia (form vision deprivation amblyopia) in order to study the symptomatology and the results of treatment by intensive occlusion of the sound eye. The occlusion was classified into three categories: (1) Short-term total occlusion after entropion or other minor lid surgery, (2) Long-term total occlusion lasting more than 2 weeks as a consequence of unilateral congenital or traumatic cataract, (3) Long-term incomplete occlusion as in the case of a small punctate posterior pole cataract or a linear scar of the corneal endothelium. Ocular deviations, fixation pattern, and retinal correspondence were examined. The visual evoked response (VER) was studied with reference to the recovery of visual acuity after treatment. Th occurrence of amblyopia and the recovery of visual acuity were analysed in relation to the age at the time of occlusion and the age at the time of treatment in order to clarify the critical or sensitive period in the development of visual system in humans.