Effects of neck muscles proprioception on eye position and vergence movements

Abstract

Perception of gaze direction can be influenced not only by visual input but also by extraretinal information from eye and neck muscle proprioception. Vibration of neck muscles with the head fixed is known to induce a visual illusory movement of a fixated object. A study of the effects of neck muscles proprioception on eye position and vergence movements has not been done before. Aims of this study are to investigate: 1) the effects of neck muscle proprioception on eye position during steady fixation; 2) the dynamics of the accommodative vergence movements driven by the dominant and non-dominant eye; 3) the effect of neck proprioception on accommodative vergence movements, driven by each eye. Subjects sat on a chair with the head fixed and one eye covered. Vibration was applied on three groups of neck muscles, two of which turn the head horizontally and the third group extend the head when the muscles contract. Accommodative stimulation was presented by a bar of LEDs lit in sequence. Eye movements were measured by an infrared system (Ober-2) during three stimulation conditions: 1). Vibration on neck muscles alone; 2). Accommodative stimulation alone in monocular viewing by each eye; 3). Vibration on neck muscles of the groups which turn the head horizontally, in combination with accommodative stimulation. Neck muscles vibration during fixation of a steady visual target could induce eye position changes which were related in directions to the muscles vibrated. During accommodative stimulation alone, the dynamics of vergence movements were different depending on whether the dominant or the non-dominant eye was driving the accommodation. The gain was higher when the non-dominant eye was fixating. Vibration on the neck muscles shortened the time constant of the accommodative vergence movement to square wave stimulation by the non-dominant eye. Extraretinal signals from neck proprioceptions could influence the static eye position, and the dynamics of accommodative vergence.