Effects of enucleation of the fixating eye on strabismic amblyopia in monkeys

The effects of enucleation of the fixating eye on the visual function of the deviating eye were studied in two rhesus monkeys with strabismic amblyopia. An esotropia was surgically induced when the monkeys were approximately 1 mo of age, and the fixating eyes were then enucleated at age 3 yr 11 mo. Four measures of visual function (photopic increment-threshold spectral sensitivity, scotopic spectral sensitivity, spatial modulation sensitivity, and temporal modulation sensitivity) were determined for both eyes prior to enucleation and for the deviating eyes over an 11-month period following the surgical removal of the fixating eye. Both monkeys showed some recovery of contrast sensitivity of their deviating eyes. The extrapolated cut-off values for their spatial modulation sensitivity functions increased from .27 to 2.8 c/deg for one animal and from .28 to 6.3 c/deg for the other. The extrapolated cut-off frequencies for the temporal modulation sensitivity functions of both animals showed an increase of 20-25 Hz compared to the pre-enucleation values. The spectral sensitivity functions of one monkey recovered to near normal values following enucleation, while both the photopic and scotopic functions of the other animal remained at pre-enucleation levels. Overall, the results of the experiments indicate that the removal of the fixating eyes of monkeys with strabismic amblyopia can result in significant improvements in the functional capacity of their deviating eyes.