Adaptive changes of the otolith-ocular reflex after injury to the trochlea

Abstract

In a case of superior oblique eye muscle palsy due to an injury of the trochlear region, a Bielschowsky head-tilt phenomenon (BHP) of 28° was found. As calculated in a computer model of eye movements by D. A. Robinson, this large amount of the BHP cannot be explained by the traditional concept that assumes the change in vertical deviation is merely due to the loss of downward torque of the paretic superior oblique muscle in ocular counterrolling. Rather, an increased gain of the otolith-ocular reflex affecting the vertical rectus muscles has to be postulated. Unusually large counterrolling of the non-paretic eye that subsided, together with the BHP, after corrective surgery in the paretic eye, suggested that the increased gain of the otolith-ocular reflex affected all muscles of both eyes that normally participate in ocular counter-rolling, with the only exception of the paretic superior oblique muscle. It is speculated that the increased gain of the otolith-ocular reflex could be an adaptive phenomenon for the sake of minimizing the contralateral head-tilt required for binocular vision.

Key Words:

• Bielschowsky head-tilt phenomenon
• ocular counterrolling
• otolith-ocular reflex
• superior oblique eye muscle palsy
• trochlear palsy