skew deviation
Skew deviation is a vertical misalignment of the eyes caused by a prenuclear lesion of the vertical vestibulo-ocular pathways in the brainstem or cerebellum.1 Brainstem strokes and tumors are the most common causes.2 The deviation is usually comitant and is frequently associated with cyclotorsion of one or both eyes.1
Skew deviation combined with ocular torsion and a head tilt is called the ocular-tilt reaction, and the triad results from dysfunction of the utricular pathways that run from the labyrinths to the rostral brainstem.2 A noncomitant skew deviation can be hard to tell from a fourth nerve palsy, because both may give a positive head-tilt or three-step test.2 Torsion helps separate them.2 In skew deviation both eyes are torted, with the higher eye usually incyclorotated and the lower eye excyclorotated, whereas a fourth nerve palsy excyclorotates the hypertropic eye alone.2 The vertical deviation and torsion of a skew deviation also decrease with the patient supine, but those of a trochlear nerve palsy stay the same.2
More detail
The upright-supine test helps confirm the diagnosis.3 The patient fixates an object 1/3 meter away, alignment is measured upright and then supine, and a decrease of more than 50% in the vertical deviation in the supine position is a positive result.3 With lesions of the midbrain or upper pons the contralateral eye is lower (contraversive skew), and with lesions of the lower pons or medulla the ipsilateral eye is lower (ipsiversive skew).1 Fourth nerve palsy and myasthenia gravis can occasionally present in a similar fashion.3
Treatment options include prismatic correction in spectacles, botulinum injections and, in persistent cases, vertical muscle surgery.3
Sources (8)
- Yanoff and Duker, Ophthalmology (2023), part 9
- Liu, Volpe and Galetta, Neuro-Ophthalmology: Diagnosis and Management, ch. 15
- Kanski, Clinical Ophthalmology (2024), ch. 19
- Brodsky, M.C., Donahue, S.P., Vaphiades, M. and Brandt, T. 2006. Skew deviation revisited. Survey of Ophthalmology, 51(2), pp.105-128.
- Keane, J.R. 1975. Ocular skew deviation: analysis of 100 cases. Archives of Neurology, 32(3), pp.185-190.
- Rutstein, R. and Daum, K. 1997. Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
- Wong, A.M. and Sharpe, J.A. 2005. Representation of static eye positions in three-dimensional space. Vision Research, 45(4), pp.501-515.
- Wong, A.M., Tweed, D. and Sharpe, J.A. 2002. Deficits in position constancy in one incomitant strabismus. Investigative Ophthalmology & Visual Science, 43(13), pp.4305-4311.
Reviewed October 2026