Monocular "pinball" saccadic intrusions and ophthalmoparesis in spinocerebellar ataxia type 3

From an ocular motor and vestibular standpoint, patients with spinocerebellar ataxia type 3 (SCA 3) may present with downbeat nystagmus, gaze-evoked nystagmus, ophthalmoparesis and/or vestibular loss. This patient had gaze-evoked nystagmus and ophthalmoparesis (vertically and horizontally, more abduction paresis than adduction) with proportionally slow saccades. Additionally, there was eyelid myokymia, and monocular adducting saccadic pulses ("pinball" intrusions, which lack a return saccade), which have been reported in SCA 3. These monocular intrusions may be a reflection of equal innervation to yoked muscle pairs in accordance with Herring's law in lateral gaze (e.g., an adducting nystagmus due to predominant abduction paresis akin to an abducting nystagmus due to adduction paresis with an internuclear ophthalmoplegia), or when occurring spontaneously, perhaps represent impaired control of the saccadic machinery (e.g., paramedian pontine reticular formation, PPRF), monocular or asymmetric output from PPRF to ocular motor nuclei, and/or related to her ophthalmoparesis and convergent strabismus.