Unusual monocular pendular nystagmus in multiple sclerosis.

Two unusual cases of monocular pendular nystagmus in patients with multiple sclerosis are reported. One patient showed regular horizontal oscillations of the right eye in abduction, associated with right abduction paresis. The second patient had a similar abnormal eye movement of the left eye in adduction, with partial left internuclear ophthalmoplegia. Such eye position–dependent monocular pendular nystagmus provides new insights into pathogenic mechanism for acquired pendular nystagmus. Different mechanisms are discussed such as the combination of paresis and commonly accepted hypothesis of dysfunction of visual and/or motor feedback loops in the ocular motor neural network. Journal of Neuro-Ophthalmology 2011;31:38–41 doi: 10.1097/WNO.0b013e3181f8dc23 2011 by North American Neuro-Ophthalmology Society T he most frequently reported eye movement disorders in multiple sclerosis (MS) are internuclear ophthalmoplegia, isolated ocular motor palsy, gaze-evoked nystagmus, and pendular nystagmus (1). Pendular nystagmus is characterized by quasi-sinusoidal oscillations of the eyes along a horizontal, vertical, or torsional direction. Pendular nystagmus in MS may be asymmetrical and in this case, most frequently of greater amplitude in the eye with poorer vision (2). Strictly, monocular forms of pendular nystagmus in MS have been reported, either associated with chronic visual deficit following optic neuropathy (2,3) or observed during convergence (4). We report 2 patients with MS with monocular horizontal pendular nystagmus, which was specifically triggered in eccentric gaze.