Ocular Counter-Roll Is Decreased After Vertical Vergence Adaptation

Abstract

Purpose: : Ocular counter-roll is a reflex that allows the horizontal meridian of the retina to remain more parallel to the earth horizontal during head roll. The gain of this reflex is reduced by horizontal convergence and by cerebellar disease causing vertical ocular misalignment. We examined the effect of vertical vergence training on ocular counter-roll gain.

Methods: : A tilting haploscopic viewing device with circular targets spanning >54 degrees was used to stimulate vertical vergence. Normal subjects were trained to vertical target disparity for 30 minutes, causing a transient cyclovertical ocular deviation. Static ocular counter roll for 45 degree head tilt was measured from 15 to 60 seconds after completion of head rotation. Eye movements were recorded with a video eye tracker mounted on the haploscope. Ocular torsion was determined with a polar correlation algorithm, using natural iris landmarks.

Results: : Prior to vergence adaptation, static ocular counter-roll varied from 0.5 to 7.7 degrees with 45 degree head roll (gain 0.01 to 0.17) for both eyes. The difference in torsion rotation between eyes averaged 0.6 degrees. After vertical vergence stimulation, static ocular counter-roll decreased by 1.2 degrees (23%) for both eyes (P < 0.001 by paired t-test).

Conclusions: : Static ocular counter-roll varied considerably in normal individuals and was decreased after vertical vergence training. Vertical vergence tone may modulate torsion eye position.

Keywords: adaptation: motion • vergence • vestibulo-ocular reflex