Skew Deviation Revisited

Ocular tilt reaction. Top Left: Facial photograph shows mild left head tilt. Top Right: Fundus photographs show intorsion of the right eye and extorsion of the left eye. Bottom left: MR imaging shows focal lesion involving the right medial longitudinal fasciculus. Bottom right: Diagram depicting causative lesion. (Reprinted from Vaphiades²⁰⁵ with permission of Wisconsin University Press.)

Figure showing physiologic and pathologic skew deviation. In the physiologic ocular tilt reaction (left), the compensatory head tilt predominates, with only a small skew deviation or static ocular counterroll. In the pathologic ocular tilt reaction (right), all three components of the ocular tilt reaction are present. (Reprinted from Brodsky³⁷ with permission of the American Medical Association.)

Physiologic ocular tilt reaction in a motorcycle rider when tilted in the roll plane. (Reprinted with permission from Bike magazine, p 74, August 2001.)

Figure showing close anatomical correspondence between semicircular canals and extraocular muscles in man. (Reprinted from Simpson and Graf¹⁷⁶ with permission of the New York Academy of Sciences.)

Vesitibulo-ocular connections showing showing extraocular muscles activated by individual semicircular canals (I = ipsilateral; c = contralateral). Central connections through the vestibular nucleus are not shown.

Graviceptive pathways from the otoliths and vertical semicircular canals mediating the vestibular reactions in the roll plane. The projections from the otoliths and the vertical semicircular canals to the ocular motor nuclei (trochlear nucleus IV, oculomotor nucleus III, abducens nucleus VI), and the supranuclear centers of the interstitial nucleus of Cajal (INC), and the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) are shown. They subserve vestibuloocular reflex (VOR) in three planes. The VOR is part of a more complex vestibular reaction that also involves vestibulospinal connections via the medial and lateral vestibulospinal tracts for head and body posture control. Note that graviceptive vestibular pathways for the roll plane cross at the pontine level. Ocular tilt reaction is depicted schematically on the right in relation to the level of the lesion (i.e., ipsiversive with peripheral and pontomedullary lesions, and a contraversive with pontomesencephalic lesions). In vestibular thalamus lesions, the tilts of the subjective visual vertical may be contraversive or ipsiversive. (Reprinted from Brandt and Dieterich²⁵ with permission of Wiley.)

Figure showing different types of skew deviation that can result from selective unilateral injury to otolithic either the anterior or posterior semicircular canals. These asymmetric injuries provide an explanation for incomitant forms of skew deviation.

Lateral alternating skew deviation. Top: Diagram depicting the ocular motor affects of bilateral prenuclear lesions affecting otolithic pathways corresponding to the anterior semicircular canals. These lesions would activate the posterior semicircular canals which excite all four depressors. The greater torsional actions of the superior oblique muscles in primary position also produces static intorsion of the globes. Bottom: Because the vertical actions of the oblique and rectus muscles summate in adduction (the oblique muscles have mainly a torsional effect in abduction), this disorder results in laterally alternating skew deviation with overdepression of the adducting eye. (Reprinted from Brodsky and Donahue³⁸ with permission of the American Medical Association.)

Ocular tilt reaction simulating superior oblique palsy. Top left: Facial photograph demonstrates a left head turn and a slight head tilt. Top right: Field measurements are consistent with right superior oblique palsy (HT = hypertropia). Bottom left and right: Retinal photographs show intorsion of the higher eye and extorsion of the lower eye which signifies an ocular tilt reaction. (Reprinted from Donahue et al⁶⁸ with permission of the American Medical Association.)

Dissociated vertical divergence. In the patient with congenital strabismus, unequal binocular visual input exerts the same physiologic effect as unbalanced utricular input, producing a combined vertical divergence and cycloversion of the eyes. In DVD, however, the cycloversion movement is opposite in direction to that seen with the utricular ocular tilt reaction. (Reprinted from Brodsky³⁶ with permission of the American Medical Association.)