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.