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Laura Renninger, Linh Dang, Preeti Verghese, Donald Fletcher; Effect of central scotoma on eye movement behavior. Journal of Vision 2008;8(6):641. doi: 10.1167/8.6.641.
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In low vision rehabilitation, patients with central vision loss are taught to use their peripheral vision to perform tasks once done by the fovea (e.g. reading). Patients are taught eccentric viewing techniques in conjunction with visual aids such as magnifiers. Scanning strategies may also be taught (e.g. look into the blind field for missing information), however it is not clear how eye movements may compensate for visual field loss. Using methods described previously (Renninger, et. al. JOV 2007) we compute the information gained by subjects as they perform an adaptive shape discrimination task. The difference between the comparison shapes is adjusted to maintain discrimination performance at 75% correct and allow comparison between normally-sighted individuals (20/20) and patients with low vision (20/200 – 20/700). The efficiency of the eye movement strategy is taken as the ratio of information gained at a given fixation location, divided by the maximum gain possible. The computation takes into account the size and location of the scotoma, as measured by microperimetry with a scanning laser ophthalmoscope. Eye movement parameters such as fixation dwell time and saccade amplitude were also measured. Results: Fixation dwell times varied substantially and were negatively correlated with saccade amplitudes, however no difference was observed in these eye movement parameters between normal and low vision subjects. Low vision patients with smaller scotoma (∼5deg) made highly efficient eye movements, similar to normally-sighted individuals. As scotoma size increased (up to 20deg), efficiency declined rapidly and even fell below chance levels in the most advanced cases. Conclusion: Extensive field loss may further impair functional vision by reducing the ability of subjects to select and prepare saccades to points of high information in the visual field. Rehabilitation that seeks to increase eye movement efficiency may help patients, especially those with moderate central field loss.
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