Electrical stimulation of superior colliculus affects strabismus angle in monkey models for strabismus

Area of Science:

• Neuroscience
• Ophthalmology
• Developmental Biology

Background:

• Disrupted binocular vision during critical developmental periods causes strabismus (eye misalignment) in humans and animal models.
• Vergence circuit disruption is a proposed neural basis for strabismus.
• Electrical stimulation of the rostral superior colliculus (rSC) elicits vergence eye movements in normal monkeys.

Purpose of the Study:

• To investigate the impact of superior colliculus (SC) stimulation on eye misalignment in strabismic monkeys.
• To determine if SC stimulation can modulate the horizontal strabismus angle.

Main Methods:

• Electrical stimulation (400 Hz, 0.5-s duration, 10-40 μA) was applied to 51 sites in the intermediate and deep SC layers of 3 adult strabismic monkeys.
• Eye movements were recorded using scleral search coils during a fixation task.
• Analysis focused on saccade characteristics and changes in horizontal strabismus angle.

Main Results:

• Electrical stimulation induced significant changes in horizontal strabismus, shifting it towards exo- or esotropia depending on the stimulation site.
• While saccade amplitudes were similar between eyes, saccade directions differed, contributing to disconjugacy.
• Disconjugate saccadic and postsaccadic movements each accounted for approximately 50% of the observed change in horizontal misalignment.

Conclusions:

• Electrical stimulation of the SC in strabismic monkeys alters horizontal eye alignment.
• The observed changes result from a combination of disconjugate saccadic and postsaccadic eye movements.
• These findings support the hypothesis that developmental disruption of vergence circuits contributes to the maintenance of strabismus.