Walsh & Hoyt: Skew Deviation and the Ocular Tilt Reaction

Skew deviation is a vertical misalignment of the visual axes caused by a disturbance of prenuclear vestibular inputs to the oculomotor nuclei. Torsional and horizontal deviations may be associated findings. The hypertropia may be the same (comitant) in all positions of gaze, or it may vary and even alternate (typically with an alternating abducting hypertropiai.e., right hypertropia on right gaze, left hypertropia on left gaze). When skew deviation is incomitant, it may mimic an isolated superior or inferior oblique palsy by the Bielschowsky three-step test. In such cases, however, it appears that the addition of a fourth step, assessment of ocular torsion in both eyes, may be able to distinguish skew deviation from isolated oblique weakness: with skew mimicking superior oblique palsy, the hypertropic eye is incyclotorted (rather than excyclotorted, as one would expect if the hypertropia were the result of superior oblique weakness). By analogy, when skew mimics inferior oblique palsy, the hypotropic eye is excyclotorted (rather than incyclotorted, as one would expect if the hypotropia were the result of inferior oblique weakness). It remains to be seen, however, whether the addition of this fourth step will reliably distinguish between superior oblique palsy and all forms of skew deviation, or whether some cases will simply be indistinguishable at the bedside.