Pendular nystagmus and oculopalatal tremor.

Abstract: Acquired pendular nystagmus consists of quasi-sinusoidal oscillations of the eyes that significantly impair gaze stability and visual clarity. It most commonly occurs in demyelinating disorders such as multiple sclerosis and in acquired degenerative conditions like oculopalatal tremor. Other etiologies-including drug toxicity, metabolic and genetic disorders, and granulomatous diseases-can also produce syndromes featuring pendular nystagmus. Analysis of its kinematic properties has provided clues to the underlying mechanisms of this otherwise enigmatic disorder. In this review, we examine the clinical features of neurological conditions associated with pendular nystagmus, with emphasis on its acquired forms, and summarize recent advances in diagnostic strategies and therapeutic development. Pendular nystagmus is defined by quasi-sinusoidal oscillations of the eyes that impair visual acuity and produce oscillopsia.1 Despite its designation as "nystagmus," this disorder lacks the hallmark waveform of classical nystagmus-slow drifts followed by rapid corrective saccades. Instead, pendular nystagmus consists of consecutive slow phases of eye movement, giving it a pendular appearance. These oscillations typically exhibit a dominant frequency of 4 to 6 Hz, although certain conditions, such as oculopalatal tremor (OPT; see below), present with lower frequencies around 2 Hz, while demyelinating disorders may reach frequencies up to 8 Hz. The phenomenology of pendular nystagmus reflects diverse underlying pathophysiological mechanisms associated with neurodegenerative, toxic-metabolic, immune-mediated, and genetic disorders. This review aims to provide a comprehensive resource on the pathophysiology, phenomenology, etiology, and therapy of pendular nystagmus.