Ocular Torsional Instability—A Neurodiagnostic Sign of Prenuclear Disease

Abstract

Background: Accurate diagnosis of efferent visual system disease in neuro-ophthalmology involves the classification of clinical signs as prenuclear, nuclear, or infranuclear in origin. Over many years, I have come to recognize ocular torsional instability as a clinical sign of prenuclear disease. Methods: Retrospective chart review of patients in whom ocular torsional instability was diagnosed using indirect ophthalmoscopy. Results: Twenty patients were diagnosed as having ocular torsional instability (OTI). Eight had neuro-ophthalmologic disease caused by structural injury to prenuclear ocular motor areas. Six of these had structural lesions primarily involving the cerebellum, one had a midbrain glioma, and one had traumatic encephalomalacia. Eight additional patients had infantile strabismus (esotropia in 7, exotropia in 1) associated with various combinations of monocular nasotemporal optokinetic asymmetry, latent nystagmus, and dissociated vertical divergence (DVD), indicating prenuclear involvement of subcortical visuovestibular pathways within the brain. Three additional patients presented with intermittent exotropia with DVD signifying early onset, while 2 had acquired esotropia that was noninfantile in origin. One had partially accommodative esotropia with bilateral inferior oblique overaction, and one presented with acquired esotropia followed by spontaneous secondary exotropia. Conclusions: OTI provides a useful clinical sign of prenuclear ocular motor dysfunction. When detected in patients without any signs of infantile or early-onset strabismus, OTI signifies the need for neuroimaging to rule out neurovestibular or cerebellar causes of prenuclear disease.