Interocular alignment following visual deprivation in the cat.

Kittens were placed in the dark just after birth and then removed at various ages for the study of interocular alignment. It was found that kittens dark-reared for 4 months or longer were characteristically incyclotorted with respect to normal animals. Deprivation periods of less than 2 months were ineffective in producing these changes. Divergence of the visual axes was also observed in some dark-reared cats. Pupillary constriction in response to light was much more pronounced in dark-reared cats than in normal cats. This enhanced pupillary reaction persisted for at least 3 weeks after the deprived animals were brought into an illuninated environment. When dark-reared cats were allowed a recovery period in a normally lit visual environment, their ocular alignment changed markedly. The incyclotorsion and divergence of the visual axes disappeared, and instead cats allowed recovery from deprivation could display excyclotorsion and/or convergence of the visual axes. These anomalies of ocular alignment associated with the recovery from visual deprivation could occur following periods of initial deprivation as short as 30 days or as long as 2 years. The mechanisms and possible significance of such anomalies are considered.