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Sustained fixation induced changes in phoria and convergence peak velocity
Eun H Kim1, Vincent R Vicci, Sang J Han
1Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States of America.
Plos One
|June 24, 2011
Summary
Phoria adaptation significantly altered convergence peak velocity, with near adaptation speeding up responses more than far adaptation. This suggests prisms could help manage visual discomfort by influencing eye movements.
Area of Science:
- Ophthalmology
- Neuroscience
- Vision Science
Background:
- Phoria, a latent eye deviation, can adapt to sustained visual demands.
- Convergence, the inward turning of both eyes, is crucial for near vision.
Purpose of the Study:
- To examine how phoria adaptation influences the speed of convergence eye movements.
- To determine if initial vergence position affects this relationship.
Main Methods:
- Six subjects with normal binocular vision underwent sustained fixation tasks (1° and 16°).
- Convergence step responses and near dissociated phoria were measured using an infrared limbus tracking system.
- Peak velocity of convergence was analyzed at different initial vergence positions (1° and 12°).
Main Results:
- Sustained fixation led to significant phoria adaptation.
- Convergence 'far' steps (1°) were faster than 'near' steps (12°).
- Near phoria adaptation resulted in faster convergence steps than far phoria adaptation.
Conclusions:
- Phoria adaptation modifies convergence peak velocity, with near adaptation having a greater effect.
- Findings suggest potential clinical applications for prisms in managing visual discomfort by modulating eye movements.
- Further research is needed on prism effects on convergence and divergence in spectacle wearers.
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