Acquired Monocular Nystagmus in Adults: Etiology, Mechanisms, and Clinical Implications

Background Acquired monocular nystagmus is a rare and diagnostically challenging condition that contrasts with the typical binocular and conjugate nature of nystagmus. The aim of this study was to systematically review reported cases of acquired monocular nystagmus in adults, focusing on underlying etiologies, clinical features, neuroimaging results, and proposed pathophysiological mechanisms. Methods A systematic review was conducted following PRISMA 2020 guidelines. PubMed, Web of Science, and Scopus were searched on 24 February 2026 for studies reporting acquired monocular nystagmus in adults. Eligible studies included case reports or series with extractable patient-level data. Additionally, two illustrative cases are presented. Data were synthesized narratively. Results Eighteen studies with 32 published cases, along with two additional cases, involved 34 patients. The median age was 40 years (range 19–63), with a female predominance (59%). Multiple sclerosis was the most common underlying condition (47%). Reduced visual acuity in the affected eye was observed in 82%, and oscillopsia in 56%. Pendular nystagmus was most common (88%), predominantly vertical. Neuroimaging frequently showed brainstem and periventricular lesions. The most frequent mechanism was combined sensory deprivation and neural integrator dysfunction (32%), followed by sensory deprivation alone (29%) and isolated neural integrator dysfunction (21%). The clinical course was mostly chronic (91%), with an often prolonged delay between visual loss and onset. Conclusion Acquired monocular nystagmus arises from the interaction between asymmetric sensory input and focal disruption of central ocular motor networks. Recognition should prompt evaluation of both visual pathways and brainstem ocular motor systems.