Interocular interactions in esotropia.

In cats the unilateral convergent strabismus surgically induced in the early postnatal life causes monocular spatial vision deficits and loss of binocular activation of the primary visual cortex. It is assumed that the asynchrony of inputs from the two eyes, by disrupting binocular convergence, leads to unbalanced binocular interactions that favour the non-deviated eye. The competitive advantage of this eye reduces both the excitatory drive to the cortex and the behavioural visual capabilities of the strabismic eye that exhibits the loss of the nasal portion of the visual field. Our experimental evidence indicate that the esotropic input, released by interocular influences by the chiasm section, recovers at least as much effectiveness to achieve orienting reactions in the previously neglected nasal field. In addition we found that the excitatory drive of the ipsilateral strabismic input, which is the one mostly impaired in esotropic animals, is fully preserved when the interocular interactions are impeded at birth and it is greatly improved in the esotropic cats with section of the optic chiasm performed in adulthood. All together these results suggest that functional impairment of the esotropic input prior of chiasmotomy does not reflect developmental changes of the visual afferents yet the active inhibition exerted by interocular mechanisms.