Eye position changes induced by neck muscle vibration in strabismic subjects.

BACKGROUND

In normal subjects vibratory stimulation of neck muscle proprioceptors can induce eye position change and visual illusory movement. The direction of apparent movement is vertical when the back muscles of the neck are stimulated and horizontal when lateral-rotation muscles are stimulated. The effect of muscle proprioceptor stimulation in individuals with defects in binocular vision, such as strabismus, has not been studied previously and is the subject of the present report.

METHODS

In 23 strabismic patients with different levels of binocular vision, 70-Hz mechanical vibration was applied to three groups of neck muscles under both dark and normal light conditions, and eye position changes were recorded for each eye using an infrared reflection technique. The dominant eye fixated on a target while the non-dominant eye was covered.

RESULTS

When the back muscles were stimulated, eye position changed in a downward direction, as previously demonstrated in the normal subjects. However, in strabismic subjects with poor binocular vision, stimulation of the horizontal rotation neck muscles resulted in eye position changes generally to the same side regardless of the muscle group activated. This differed from normal subjects, where the direction of the eye position changes is related to the group of muscles stimulated. The direction and amplitude of the eye position changes were the same under dark and light conditions.

CONCLUSION

Proprioceptive information from neck muscles plays an important role in regulation of gaze direction. The difference that exists between normal subjects and strabismic patients is most likely related to differences in binocular function.