Cortical binocularity in convergent strabismus after section of the optic chiasm

Area of Science:

• Neuroscience
• Ophthalmology
• Visual System Research

Background:

• Convergent strabismus (esotropia) leads to functional advantage of the nondeviated eye and inhibition of the esotropic eye due to spatial asynchrony.
• Strabismic suppression is hypothesized to result from inhibitory interocular interactions.
• Interrupting interocular pathways at the optic chiasm could potentially remove strabismic suppression.

Purpose of the Study:

• To investigate the role of interocular pathways in strabismic suppression.
• To determine if sectioning the optic chiasm in adult strabismic cats restores cortical responsiveness of the esotropic eye.
• To analyze cortical activation patterns and binocularity after optic chiasm section.

Main Methods:

• Electrophysiological recordings from the striate cortex of adult cats with induced convergent strabismus.
• Surgical section of the optic chiasm in strabismic cats.
• Stimulation of both deviated and nondeviated eyes to assess cortical responsiveness and neuronal activation.

Main Results:

• Cortical responsiveness to the strabismic eye significantly increased after optic chiasm section compared to intact controls.
• Stimulation effectiveness of the deviated eye matched the nondeviated eye in driving cortical neurons.
• Significant binocular activation was observed in the cortex ipsilateral to the deviated eye, while the contralateral cortex remained largely monocularly driven.

Conclusions:

• The impaired effectiveness of esotropic input is due to active inhibitory influences via interocular pathways, not developmental deficits.
• Strabismic suppression is mediated by interocular mechanisms similar to those in binocular rivalry.
• Restoring input from the deviated eye is possible by disrupting interocular inhibitory pathways.