Slow control of eye position in strabismic amblyopia.

Unsteady and eccentric monocular fixation were examined in subjects with strabismic amblyopia. Records of horizontal components of unsteady fixation by amblyopic eyes were characterized by abnormally large saccades and a nasalward bias for slow drifts. Typically, these fixational movements aligned the retinal image on an eccentric nasal retinal region. The presence of a slow control mechanism for eye position in amblyopia was examined by teaching subjects to voluntarily suppress fixation saccades. In the absence of saccades, amblyopic eyes continued to fixate eccentrically, using slow drifting movements. When attempting to fixate in the dark, fast drifts moved an amblyopic eye several degrees from its usual eccentric fixation posture, and large saccades were necessary to control eye position. Results demonstrate the operation of a slow control mechanism for eye position in amblyopia.