Functional impact of fixational eye movements in central vision loss

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PROJECT SUMMARY/ABSTRACT People who lose their central (foveal) vision due to macular disorders such as age-related macular degeneration or other retinal diseases often suffer from poor vision that cannot be corrected optically, surgically or therapeutically. To date, there is no promising cure for macular disorders, and there is no intervention that can reverse the vision loss. Previous efforts to understand why vision is so difficult for people with central vision loss have focused mainly on the spatial properties associated with using the peripheral retina. This project examines a different factor — the effects due to fixational eye movements. Most individuals with central vision loss have unsteady fixation, resulting in greater retinal image motion than that found in people with normal vision. The clinical wisdom is that exaggerated fixational eye movements are detrimental for vision. Is it really so? People with central vision loss must use their peripheral vision, therefore, potentially the exaggerated fixational eye movements are beneficial because they prevent images on the peripheral retina from fading. This research will be the first attempt in providing scientific evidence to understand the relationship between fixational eye movements and functional vision in people with central vision loss. The first aim of the proposed research project is to test the hypothesis that the retinal image motion associated with fixational eye movements exhibited by people with central vision loss is suboptimal for them to see “fine” details. We will evaluate how performance for fine spatial tasks changes with the amount of retinal image motion, generated by stabilizing (to different extent) a stimulus on the retina using an eye-tracking scanning laser ophthalmoscope. We expect that performance vs. the amount of retinal image motion would demonstrate tuning: Too little retinal image motion would cause perceptual fading (poorer vision) and too much retinal image motion would be detrimental for seeing spatial details. We predict that for any given individual with central vision loss, there is an optimal level of retinal image motion that yields the best functional vision, which may not correspond to that due to the natural fixational eye movements of the individual. The second aim of the proposed research project is to test the hypothesis that retinal image motion due to abnormal fixational eye movements can be reduced through fixation training. More importantly, the improved fixation stability after training will be accompanied by improvements in functional vision. We will compare performance on several common visual tasks, and the shape of the tuning function as described in the first aim, before and after fixation training to evaluate the efficacy of the fixation training. Retention of the training effect will also be examined. The findings from this project will help us understand the role of fixational eye movements in limiting vision for people with central vision loss, and how we can use the information to develop useful and more effective rehabilitative methods or tools to improve the functional vision for patients with central vision loss.