Comparison of oculomotor findings in the progressive ataxia syndromes.

In this study we compare the results of quantitative oculomotor function testing in patients with Friedreich's ataxia (FA), olivopontocerebellar atrophy (OPCA) and cerebello-olivary atrophy (CA). Common features in all three syndromes included gaze-evoked nystagmus, saccade dysmetria and prolonged saccade reaction times. Patients with FA showed a characteristic combination of frequent saccadic intrusions, especially ocular flutter, relatively preserved optokinetic nystagmus (OKN) and smooth pursuit, and impaired vestibulo-ocular reflex (VOR) responses. In patients with CA saccadic intrusions were infrequent, OKN and smooth pursuit were severely impaired and VOR gain was normal or increased. Results in OPCA were more variable. When present, slowing of saccades or the combined loss of pursuit and vestibular function were characteristic for OPCA. The ability to suppress the VOR with a head fixed target was relatively preserved in FA, normal to moderately impaired in OPCA and always severely impaired in CA. We conclude that oculomotor testing is useful in the differential diagnosis of the progressive ataxia syndromes.