Vertical Misalignment in Skew Deviation vs. Trochlear Nerve Palsy: Dependence on Head Orientation

Abstract

Purpose: : Skew deviation is a vertical strabismus caused by supranuclear or peripheral vestibular lesions. It has been attributed to imbalance of the vestibulo-ocular reflex projections from the utricles to ocular motoneurons. The utricles normally detect static positions (tilts) of the head. We previously reported that the abnormal ocular torsion is head position-dependent in skew deviation, but not in trochlear nerve palsy. The purpose of this study is to investigate whether the vertical misalignment in skew deviation differs in upright vs supine position, and to compare these findings with those in peripheral trochlear nerve palsy in a larger series of subjects.

Methods: : Ten patients with skew deviation, 14 with trochlear nerve palsy, and 12 normal subjects were recruited. Vertical misalignment was measured by the prism and alternate cover test while the subjects fixated a target at 1 m. The test was performed in upright and supine positions. Changes in vertical misalignment were measured by calculating a vertical change index (VCI), defined as (V_up - V_supine)/ (V_up + V_supine), where V_up is vertical misalignment in upright and V_supine is vertical misalignment in supine position.

Results: : In skew deviation, the magnitude of vertical misalignment decreased substantially or disappeared completely in supine position, whereas in peripheral trochlear nerve palsy, there was little or no change between different positions. The mean VCI was 0.74 ± 0.34 in skew deviation, -0.05 ± 0.09 in trochlear nerve palsy, and -0.06 ± 0.14 in control subjects (ANOVA, p<0.001).

Conclusions: : Our previous and present results provide the basis of additional tests which could be used clinically to differentiate trochlear nerve palsy from skew deviation: torsion and vertical misalignment that decrease from upright to supine position indicate skew deviation, whereas torsion and vertical misalignment that do not change between positions indicate trochlear nerve palsy.

Keywords: strabismus: diagnosis and detection • neuro-ophthalmology: diagnosis