Excitatory Contribution to Binocular Interactions in Human Visual Cortex Is Reduced in Strabismic Amblyopia

Area of Science:

• Neuroscience
• Ophthalmology
• Visual Science

Background:

• Binocular summation is typically reduced in strabismic amblyopia, attributed to impaired excitatory interocular interactions.
• Understanding these interactions is crucial for visual development and function.

Purpose of the Study:

• To investigate the roles of excitatory and suppressive interactions in binocular contrast processing in strabismic and anisometropic amblyopia.
• To compare these interactions across the visual cortical hierarchy using electrophysiological measures.

Main Methods:

• Utilized source-imaged steady-state visual evoked potentials (SSVEP) with dichoptic stimuli.
• Analyzed spectral response components (self- and intermodulation terms) across a range of interocular contrast ratios.
• Applied a contrast gain control model to quantify excitatory and suppressive contributions.

Main Results:

• Strabismic amblyopes showed significantly reduced intermodulation (IM) responses, indicating weaker interocular interactions in visual cortex compared to anisometropic amblyopes and normal vision.
• A contrast gain control model revealed that excitatory contributions were significantly reduced in V1 and extra-striate cortex in strabismic amblyopia.
• Suppressive contributions to binocular interactions remained intact in strabismic amblyopia.

Conclusions:

• Disruption of binocular interactions in strabismic amblyopia is primarily due to a preferential loss of excitatory pathways.
• These findings provide robust electrophysiological evidence supporting the deficit in excitatory interocular connections as the cause of impaired binocular vision in strabismus.