Preserved Eye Movements In Adults With Spinal Muscular Atrophy

Introduction: Spinal muscular atrophy (SMA) most prominently affects proximal limb and bulbar muscles. Despite older case descriptions, ocular motor neuron palsies or other oculomotor abnormalities are not considered part of the phenotype.Methods: We investigated oculomotor function by testing saccadic eye movements of 15 patients with SMA. Their performance was compared with that of age-matched healthy controls. Horizontal rightward and leftward saccades were recorded by means of video-oculography, whereas subjects looked at light-emitting diode targets placed at +/- 5 degrees, +/- 10 degrees, and +/- 15 degrees eccentricities.Results: No differences in saccade amplitude gains, peak velocities, peak velocity-to-amplitude ratios, or durations were observed between controls and patients. More specifically, for 5 degrees target eccentricities, patients had a mean saccadic peak velocity of 153 degrees/s, whereas for 10 degrees and 15 degrees these values were 268 degrees/s and 298 degrees/s, respectively. The corresponding mean peak velocities of the control group were 151 degrees/s, 264 degrees/s, and 291 degrees/s.Discussion: Our results indicate that patients with SMA perform fast and accurate horizontal saccades without evidence of extraocular muscle weakness. These quantitative oculomotor data corroborate clinical experience that neuro-ophthalmic symptoms in SMA are not common and, if present, should prompt suspicion for an alternative neuromuscular disorder.