Saccadic instabilities in albinism without nystagmus.

Albinism effects a surprising manipulation of the visual pathway in which some of the normally uncrossed axons of the temporal retina instead cross at the chiasm. An expected consequence of this misrouting is that subjects with albinism will have difficulty in specifying the targets of saccades. Usually albinos have nystagmus so the stability of their saccadic eye movements is not readily accessible, but some albinos do not have nystagmus. In these subjects it was found that they had frequent saccadic intrusions, the sizes of which were correlated with velocities of steady drifts in fixations (r = 0.802, P < 0.05). An explanation for the correlation between the amplitudes of the intrusions and the velocities of the drifts is that it is due to a common failure in the development of a saccadic system which is responsible for converting a given retinal displacement into a matching eye movement, with the extent of the failure reflecting the severity of the misrouting.