Normal Topography and Binocularity of the Superior Colliculus in Strabismus

Area of Science:

• Neuroscience
• Ophthalmology
• Primate Research

Background:

• Alternating strabismus allows either eye to initiate saccades to visual targets.
• The brain must compute accurate saccade vectors, dependent on the chosen eye.
• The superior colliculus is a critical midbrain center for saccade generation.

Purpose of the Study:

• Investigate if superior colliculus maps are shifted to compensate for strabismus.
• Determine how the brain computes saccades in alternating strabismus.
• Explore the organization of topographic maps in the superior colliculus of primates with strabismus.

Main Methods:

• Induced alternating exotropia in macaques at 1 month old.
• Mapped receptive fields in the superior colliculus using sparse noise stimuli during alternating fixation.
• Used microstimulation to compare sensory and motor maps and probed for anomalous retinal correspondence.

Main Results:

• Receptive fields were offset by ocular deviation but otherwise aligned.
• One animal showed a ∼20° clockwise rotation of left eye coordinates relative to the right eye, explained by cyclorotation of ocular fundi.
• Microstimulation accurately targeted receptive fields, similar to normal animals.
• No evidence of anomalous retinal correspondence was found.

Conclusions:

• Early-life eye misalignment does not alter superior colliculus topographic map organization.
• Binocular convergence in the superior colliculus is not disrupted by strabismus.
• Neurons remain responsive to stimulation from either eye, indicating functional adaptation.