A role for extra-ocular afferents on visually evoked cortical potential of exotropic patients

Abstract

Visually evoked cortical potentials (VECPs) were obtained from four normal subjects and 26 exodeviated patients. Checkerboard pattern shift stimuli with shift frequencies of 1 and 10 Hz were used, and peak amplitude was measured and compared. An opaque suction contact lens was inserted on the dominant eye and pulled manually medially and laterally to a deviation of about 40°. Stimuli were given to the non-dominant eye.

VECPs of patients without binocular function responded remarkably to the forced ductions. Adduction of the dominant eye caused an increase of peak amplitude to 163.5 ± 24.68, abduction an increase to 138.8 ± 28.5%, and in patients with binocular functions, peak amplitude decreased to 89.3 ± 27.3% by adduction. and decreased to 84.4 ± 28.55% by abduction. In normal subjects. peak amplitude decreased to 74.3 ± 20.35% by adduction, and decreased to 77.2 ± 12.9%. The normal subjects and the exodeviates with binocular functions responded almost identically. However, patients without binocular function responded significantly excitatory to the forced ductions. In confirmation of these results, one typical case of strabismus and monocular amblyopia was carefully studied. This patient had lost the dominant eye; correction of the eye position was carried out, and after surgery, a remarkable improvement of VECPs and visual acuity were noted.

These data suggest that changes of tonicity in extraocular muscles in the dominant eye can influence the VECPs when visual input is abolished.