Original Articles: Experimental Amblyopia in Monkeys. Further Behavioral Observations and Clinical Correlations

The effects of unilateral lid closure and artificial esotropia on the development of visual acuity were studied in visually immature rhesus monkeys (Macaca mulatta). Irreversible amblyopia occurred in all animals whose lids were sutured between birth and nine weeks of age. Lid closure at the age of 12 weeks did not produce amblyopia. During the age of susceptibility only brief periods of occlusion (two to four weeks) were effective in causing severe amblyopia. Strabismic amblyopia occurred in monkeys in which the onset of experimental esotropia was during the first week of life. Correlation of these data with those obtained from human patients indicate that the human visual system remains sensitive to unilateral lid closure for a longer period of time than that of the monkey. Clinical observations also suggest that, as in monkeys, unilateral occlusion for only brief periods during infancy may cause irreversible amblyopia and, therefore, is contraindicated.