Abstract
Abstract:
Vergence and accommodation are thought to be linked by a single unitary command in order to enable clear single vision of approaching and receding targets (as modeled by the AC/A and CA/C ratios). In many forms of strabismus, the link between accommodation and vergence is thought to be anomalous. Abnormal accommodation and convergence ratios are used to define subgroups of esotropia and exotropia, which in turn influence management. Although it is straightforward to measure normal eye alignment and strabismic deviations including vergence, measures of accommodation are usually inferred through indirect clinical tests.
Eye position and accommodation were directly and simultaneously measured in 7 normal subjects. Recordings were made from both eyes in real time as the subjects followed accommodative targets that moved smoothly in depth on the midline. Both eyes were recorded during both binocular and monocular viewing. Occlusion was done with an infrared filter that permitted recording from the occluded eye while blocking visible light.
We show that normal individuals with both eyes viewing show symmetric behavior for vergence and accommodation but symmetric ocular behavior with one eye viewing and, moreover each eye behaving differently under occlusion while accommodation response remained symmetric in the two eyes. These findings are incompatible with a strict vergence-accommodation link and suggest that normal individuals, like strabismic patients, may have some degree of independent oculomotor control.
Arvind Chandna, Jeremy Badler, and Steve Heinen.