Ocular and oculomotor signs in Joubert syndrome

A number of oculomotor defects have been described in Joubert syndrome. Thi s study systematically examined the oculomotor systems of 13 individuals pr eviously diagnosed with Joubert syndrome. Twelve had the characteristic "mo lar tooth sign" seen on magnetic resonance imaging scan. In all individuals , smooth pursuit gain and vestibule-ocular reflex cancellation were decreas ed in the horizontal and vertical directions and volitional saccades, when generated, were hypometric. We believe that these defects arise from a diso rder in the posterior cerebellar vermis. All individuals also had partial t o complete oculomotor apraxia in which initiation of saccades was prolonged or impaired. The oculomotor apraxia in Joubert syndrome differs from conge nital idiopathic oculomotor apraxia in that both volitional saccades and qu ick phases of nystagmus were impaired both in the horizontal and vertical d irections, and the defects did not resolve with time. We believe that the o culomotor apraxia arises from a disorder involving the projections from the superior colliculus to the parapontine reticular formation and rostral int erstitial nucleus of the medial longitudinal fasciculus. A subset of indivi duals also had severe visual loss, pendular nystagmus, pigmentary changes i n the fundus, and decreased vestibule-ocular reflexes. We believe that this is a form of Leber's amaurosis occasionally associated with Joubert syndro me. In summary, key oculomotor features of Joubert syndrome are decreased s mooth pursuit and vestibule-ocular reflex cancellation, partial to complete oculomotor apraxia both in the horizontal and vertical directions, and hyp ometric saccades if oculomotor apraxia is not complete.