NEURONAL CORRELATES OF AMBLYOPIA IN THE VISUAL-CORTEX OF MACAQUE MONKEYS WITH EXPERIMENTAL STRABISMUS AND ANISOMETROPIA

Amblyopia is a developmental disorder of pattern vision. After surgica l creation of esotropic strabismus in the first weeks of life or after wearing -10 diopter contact lenses in one eye to simulate anisometrop ia during the first months of life, macaques often develop amblyopia. We studied the response properties of visual cortex neurons in six amb lyopic macaques; three monkeys were anisometropic, and three were stra bismic. In all monkeys, cortical binocularity was reduced, in anisomet ropes, the amblyopic eye influenced a relatively small proportion of c ortical neurons; in strabismics, the influence of the two eyes was mor e nearly equal. The severity of amblyopia was related to the relative strength of the input of the amblyopic eye to the cortex only for the more seriously affected amblyopes. Measurements of the spatial frequen cy tuning and contrast sensitivity of cortical neurons showed few diff erences between the eyes for the three less severe amblyopes (two stra bismic and one anisometropic). In the three more severely affected ani mals (one strabismic and two anisometropic), the optimal spatial frequ ency and spatial resolution of cortical neurons driven by the amblyopi c eye were substantially and significantly lower than for neurons driv en by the nonamblyopic eye. There were no reliable differences in neur onal contrast sensitivity between the eyes. A sample of neurons record ed from cortex representing the peripheral visual field showed no inte rocular differences, suggesting that the effects of amblyopia were mor e pronounced in portions of the cortex subserving foveal vision. Quali tatively, abnormalities in both the eye dominance and spatial properti es of visual cortex neurons were related on a case-by-case basis to th e depth of amblyopia. Quantitative analysis suggests, however, that th ese abnormalities alone do not explain the full range of visual defici ts in amblyopia. Studies of extrastriate cortical areas may uncover fu rther abnormalities that explain these deficits.