The neural locus of binocular rivalry and monocular diplopia in intermittent exotropes

Patients with intermittent exotropia (strabismus) can either fixate normally or allow one eye to deviate outward by as much as 60 degrees. Two such patients (D.N. and K.C.) were studied and it was found that during eye deviation, binocular correspondence is maintained by completely 'remapping' egocentric space for the deviating eye alone using extraretinal signals from that eye. Also, by using foveal afterimages we showed that binocular rivalry occurs at a site earlier than this egocentric remapping, probably in area 17 itself. And finally, consistent with the neural remapping hypothesis, patient K.C. also experienced monocular diplopia; objects appeared double when viewed with the deviating eye.