Effects of surgically-induced unilateral exotropia on orientation anisotropy in rhesus monkey
The contrast sensitivity for sine wave gratings as a function of the grating orientation was determined for both eyes of two rhesus monkeys which had been reared with surgically-induced exotropia. The data were collected at both threshold and suprathreshold contrast levels. The fixating eyes exhibited a normal oblique effect which was slightly larger in magnitude than that of humans. The deviating eyes of both monkeys exhibited a vertical effect [reduced sensitivity for gratings with vertical orientation] rather than an oblique effect. The suprathreshold experiments showed that the vertical effect was present at approximately the same magnitude at all suprathreshold contrast levels. The presence of the vertical effect in the strabismic eyes of the monkeys is an additional parallel in the development of human and monkey and strengthens the use of the monkey as a model for the human visual system.