Spatial mapping of retinal correspondence in strabismus

Strabismus (misalignment of the visual axes of the eyes) can lead to visual confusion and diplopia. To avoid these problems, stimuli projecting onto a region of the deviating retina can be actively inhibited (inter-ocular suppression) or realigned with corresponding retinal positions in the fixating eye (anomalous retinal correspondence). Here we describe a dichoptic matching method for mapping the degree of retinal correspondence between the eyes at multiple locations in the visual field in normal and strabismic observers. Two dots, each viewed by a different eye, are positioned at corresponding locations in the visual field with reference to a central fixation cross, seen by both eyes. This positional mapping method provides good quantification of the degree of retinal correspondence in strabismus. We will present evidence for: (1) systematic shifts in positional localization that correspond to the subjective angle of squint; (2) magnified biases in regions of the central visual field that are consistent with classic patterns of suppression; and (3) a left-right hemifield asymmetry in positional correspondence that is well-correlated with the direction of squint. We will discuss these binocular distortions of visual space with reference to the associated cause of early visual deprivation.