Histological studies of the visual system in monkeys with experimental amblyopia.

Amblyopia can be produced in rhesus monkeys by suturing the lids of one eye (visual deprivation amblyopia) or by producing artificial esotropia (strabismic amblyopia) during visual immaturity. Sections from retinas, lateral geniculate nuclei (LGN), and areas 17 and 18 of the visual cortex from monkeys with behaviorally proved amblyopia and cortical neurophysiologic changes were examined histologically and compared with normal tissue. Other than significant reduction in cell section areas in all layers of the LGN that received input from the deprived or esotropic eye, we were unable to demonstrate anomalies elsewhere in the visual system. In spite of the difference in pathogenesis of visual deprivation and strabismic amblyopia, the similarity of findings in the LGN of monkeys with both types of amblyopia suggests a common mechanism. Since dissimilarity of visual input from the two eyes caused by unilateral lid suture has been shown to affect geniculate cell size in visually immature kittens, we surmise that binocular competition at the geniculate or cortical level is operative in both unilateral lid closure and strabismus and causes similar changes in the primate visual system.