Skew deviation is likely encountered clinically more often than previously thought. Cerebellar causes of skew deviation appear to be the rarest cause and should be considered by clinicians when encountering patients with findings consistent with skew deviation.

This case report describes an undiagnosed, asymptomatic skew deviation in an established glaucoma patient returning for routine follow-up. Appropriate diagnosis and subsequent neuroimaging identified a chronic ischemic cerebellar infarction.

A 72-year-old man presented for a routine glaucoma follow-up examination. Cover test revealed a 10–prism diopter left hypertropia, which worsened in right gaze and left head tilt. Double Maddox rod testing showed 5° excyclotorsion of the right eye and no torsion in the left eye. Upright-supine testing was positive. Given the patient's noticeable right head tilt, left hypertropia, increased excyclotorsion of his lower eye, and positive-upright test, the patient was diagnosed with a skew deviation. Brain MRI revealed a chronic, undiagnosed cerebellar ischemic infarction, a known cause of skew deviation and the associated ocular tilt reaction.

It can be challenging to identify skew deviations and their underlying causes. When clinically encountering a vertical deviation, appropriate tests (cover-uncover test, Parks-Bielschowsky three-step test, ocular torsion testing, and upright-supine test) are imperative to help make the correct diagnosis. Neuroimaging can then be pursued in hopes of identifying the underlying cause.