ABSTRACT
The effects of strabismus, considered as a long-term adaptation of the visual system to a monocular shift in visual direction, were studied for the spatial organization of stereoscopic depth perception. The minimum and maximum disparities for stimulating stereopsis in strabismus were examined as a function of spatial separation of disparate stimuli. Disparities and their spacing were produced by spatial modulation of two vertical lines viewed dichoptically. Most strabismics had normal upper disparity limits but elevated stereothresholds. Moderate stereothreshold elevations (100 arc sec) occurred independently of spatial separations of less than 15 arc min. A spatial crowding effect upon stereopsis resulted from the elevated lower threshold in several cases and a reduced maximum disparity limit for stereopsis in another case. Clinical tests of stereopsis that crowd stimuli closer than .25 degree underestimate the patients' optimal stereoacuities between two and fourfold. The results indicate that the spatial organization of stereopsis had not compensated for the monocular directional shift represented by the strabismic condition.
