The accuracy of fixation in lateral gaze and the problem of retinal slip.

The mean accuracy of foveal fixation in lateral gaze was measured by means of an after-image method used previously in the study of autokinesis. During physiological excursions of gaze a lag between target image and foveal image could not be demonstrated. It must be smaller than 1/1000 of the excursion. Thus there is a striking difference between the mechanism of voluntary gaze on the one hand and the mechanism of vergence on the other hand. During sustained divergence the eyes lag almost 1/10 in respect to the required vergence.