Eye movements were examined clinically in 56 patients (age range, 2-25 years; mean, 10.7 years) with ataxia telangiectasia (A-T) at Johns Hopkins University, Baltimore, MD. Electrooculographic recordings of eye movements were obtained in 33 patients. Deficits occurred in eye movement systems that stabilize images on the retina (pursuit, gaze holding, convergence, vestibular and optokinetic slow phases, and cancellation of vestibular slow phases), and in systems that maintain fixation and shift gaze, characterized by abnormal reflexive and voluntary saccades, head movements associated with gaze shifts, ocular motor apraxia, impaired fixation, and a reduction in vestibular and optokinetic quick phases. Clinical oculomotor abnormalities increased with age and were more prevalent in patients with severe neurologic abnormalities, whereas electrooculographic signs were not age or neurologic sign related. Deficits in image stabilization are associated with dysfunction in the cerebellar flocculus and ventral paraflocculus, and fixation deficits are probably correlated with dysfunction in the cerebellar vermis or the basal ganglia which affects the superior colliculus. 
COMMENT. Atrophy of the cerebellum, especially the vermis, is the most prominent structural abnormality in pathological and imaging studies of ataxia telangiectasia. Eye movement abnormalities involving stabilization of retinal images are localized in the cerebellum, whereas impairments of fixation and shifts in gaze are more likely correlated with dysfunction in the cerebellar vermis or basal ganglia.