Bilateral oculomotor abnormalities in strabismic amblyopes: evidence for a common central mechanism

The preferred eyes of strabismic amblyopes, generally presumed to be normal, have been implicated by recent studies as manifesting oculomotor abnormalities. We sought to determine whether these motor abnormalities occurred together and, if so, whether they could be related to a single underlying deficit. Occurring together in the preferred eyes of our strabismic amblyopes were: unsteady fixation (consisting of nasal drifts alternating with temporal saccades), minute fixational eccentricity (as indicated by eccentric directionalization of the Maxwell spot) and asymmetries of pursuit tracking. These motor abnormalities of the preferred eye are attributable to the presence of high-velocity nasal drifts. Since nasal drifts also account for several qualitatively similar motor abnormalities exhibited under monocular conditions by the fellow amblyopic eye, we conclude that a centrally-generated nasal drift bias is responsible for anomalous oculomotor behaviors of both eyes of strabismic amblyopes.