Is adaptation to perceived interocular differences in height explained by vertical fusional eye movements?

Area of Science:

• Ophthalmology
• Neuroscience
• Vision Science

Background:

• Vertical prisms alter retinal image height, potentially impacting binocular vision.
• Adaptation mechanisms to prism-induced visual distortions are not fully understood.
• Fusional vergence is crucial for maintaining single binocular vision.

Purpose of the Study:

• To investigate if adaptation to vertical prisms involves mechanisms beyond fusional vertical eye movements.
• To quantify prism adaptation using perceptual tests and eye tracking.

Main Methods:

• Nine visually normal subjects adapted to a 3 prism diopter base-up prism.
• Perceptual height judgments were assessed using a custom Maddox test.
• Binocular vertical eye movements were recorded using a video eye tracker.

Main Results:

• Adaptation reduced interocular perceived height differences by 51% after 15 minutes.
• Prism induced divergent vertical eye movements (1.2° average), less than expected.
• Adaptation amplitude correlated with initial perceived height differences.
• Head tilt induced larger interocular eye elevation differences than the prism.

Conclusions:

• Vertical image height differences were compensated by vertical fusional eye movements.
• Fusional eye movements were generally insufficient for full foveal realignment.
• Prism adaptation in the Maddox test was explained by vertical eye position changes, suggesting limited additional adaptational mechanisms.