Esophoria or esotropia in adulthood: a sign of cerebellar dysfunction?

Convergent strabismus is a common diagnosis in early childhood, when it is mostly considered benign. If it develops later in life, strabismus can, however, be a sign of neurological disease. In these cases the underlying pathophysiological mechanisms are largely unknown. In this retrospective case-control study we analyzed the neuro-ophthalmological examination reports of 400 adult patients who presented at the German Center for Vertigo and Balance Disorders to determine an association between ocular misalignment and cerebellar dysfunction. Patients with cerebellar signs (i.e., cerebellar ataxia and/or cerebellar ocular motor signs) had a 4.49 (95 % CI [1.60; 13.78]) times higher frequency of ocular misalignment and specifically a 13.3 (95 % CI [3.80; 55.73]) times increased frequency of esophoria/esotropia (ESO) during distant gaze than patients without cerebellar dysfunction. ESO when looking into the distance was associated with saccadic smooth pursuit, dysmetria of saccades, and downbeat nystagmus (DBN) (chi (2) test, p < 0.0001 for all associations). Patients with cerebellar dysfunction also showed mildly impaired eye abduction (chi (2) test, left eye and right eye: p < 0.0001), associated with horizontal gaze-evoked nystagmus (chi (2) test, p < 0.0001). The association of ESO and DBN implicates a pathophysiological involvement of the cerebellar flocculus, while the association with dysmetric saccades suggests involvement of the oculomotor vermis. This is compatible with animal studies showing that the pathways of the flocculus/posterior interposed nucleus and vermis/nucleus fastigii are both involved in vergence movements and static binocular alignment. From a clinical point of view, a newly diagnosed esophoria/esotropia only during distant gaze may be a sign of a cerebellar disease.