Vestibulo-ocular and optokinetic deficits in albinos with congenital nystagmus

Vestibular and optokinetic responses were recorded in three albino subjects with congenital nystagmus. Although an ice-water caloric stimulus did not elicit nystagmus, all patients showed a response to rotational stimuli containing high frequency components. Vestibular responses to a constant velocity rotation decremented with abnormally short time constants of 1-2 sec (normal 15-20 sec). For sinusoidal oscillation, in one subject, the cut-off frequency (where the amplitude of the response was 70% of maximum) was increased to 0.8 Hz (normal about 0.01 Hz). Full-field optokinetic stimulation generated no nystagmus response. These abnormalities may be due to defects in networks that act as mathematical integrators : either the final common neural gaze-holding network that converts velocity into position information for the ocular motor neurons or the "velocity-storage" mechanism that normally combines sensory inputs from both the labyrinths and visual system to generate appropriate (per-rotatory) nystagmus during rotation and to suppress inappropriate (post-rotatory) nystagmus after rotation.