Acquired Pendular Nystagmus
Acquired pendular nystagmus includes pendular, slow-phase eye movements in the horizontal, vertical, and torsional planes (often forming elliptical waveforms). In contrast, congenital pendular nystagmus usually manifests with only horizontal movements. Pendular nystagmus with both vertical and horizontal components produces oblique nystagmus (if the components are in phase) or circular or elliptical nystagmus (if the components are out of phase). The eye movements may be conjugate or disconjugate and are often dissociated.
The localizing value of acquired pendular nystagmus is poor. It is most commonly observed in patients with MS, who may exhibit asymmetric or monocular forms. This form of nystagmus can also develop after blindness occurs secondary to optic nerve disease, including optic neuropathy due to MS. When vision is reduced in both eyes, the nystagmus is typically larger in the eye with poorer vision.
Memantine or gabapentin may reduce the severity of nystagmus and improve vision in patients with acquired pendular nystagmus. Unilateral retrobulbar injection of botulinum toxin type A reduces the amplitude of nystagmus and may improve vision for patients who are willing to view monocularly. However, total cessation of eye movements has its own consequences; for example, some patients report blurred vision when walking because of the loss of the normal VOR that adjusts eye position as the head moves.
Shery T, Proudlock FA, Sarvananthan N, McLean RJ, Gottlob I. The effects of gabapentin and memantine in acquired and congenital nystagmus: a retrospective study. Br J Ophthalmol. 2006;90(7):839–843.
Thurtell MJ. Treatment of nystagmus. Semin Neurol. 2015;35(5):522–526.
Oculopalatal Myoclonus or Tremor
Acquired pendular nystagmus may accompany palatal myoclonus, an acquired oscillation of the palate. The eye movements are continuous and rhythmic, occur at a frequency of approximately 1 Hz, typically conjugate in the vertical plane, and persist during sleep. This eye movement disorder may also be associated with synchronous movements of the facial muscles, pharynx, tongue, larynx, diaphragm, trunk, and extremities. The condition usually arises several months (up to years in rare cases) after a lesion occurs that involves the Guillain-Mollaret triangle—a region that encompasses pathways that travel between the red nucleus, the inferior olivary nucleus, and the contralateral cerebellar nuclei. Lesions of this pathway produce inferior olivary hypertrophy, which is visualized with MRI as a T2 hyperintensity within 1 or both inferior olives.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.