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Preeti Verghese; Oculomotor Considerations in Macular Degeneration. Journal of Vision 2016;16(4):34-35. doi: https://doi.org/10.1167/16.4.33.
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Individuals with macular degeneration often have central field loss that includes the fovea which results in impaired high-acuity visual function and impacts eye movements that previously used the fovea as an oculomotor reference. When both eyes are affected, individuals often adopt a peripheral preferred retinal locus (PRL) for fixation. This talk addresses some of the challenges that arise from the loss of foveal vision and the adoption of an eccentric PRL, and discusses potential ways to address them.
One challenge that arises due to a central field loss is the lack of scotoma awareness. The scotoma fills in, so patients are often not aware that they are missing information in the region of the scotoma (Fletcher et al., 2012), which impacts information gathering in daily life. Low vision rehabilitation therapy is often directed towards increasing scotoma awareness. Our own work shows that practice with directing the PRL towards the scotoma to uncover a hidden target can improve information gathering and enhance performance in a visual search task.
Another challenge is that patients have to learn to use their eccentric PRL as an oculomotor reference. The difficulties associated with directing the PRL are evident in tasks such as reading, or directing eye movements to targets of interest, away from the current fixation locus. Studies show that only a small fraction of individuals with CFL direct their PRL to a jumping target (White & Bedell, 1990), or to a target that is the goal of reaching movement (Tyson et al., 2015). However, two practice regimens that use active eye movement strategies have shown success: horizontal eye movements between simple stimuli improve reading speeds in patients with CFL (Seiple et al); active search for a target in clutter and active following of a jumping target helps the development of a stable PRL and its use as an oculomotor reference, in control participants with an artificial scotoma (Kwon et al., 2013). Studies from our own lab show that individuals with CFL are able to smoothly pursue a moving target, although pursuit gain depends on the target trajectory with respect to the scotoma.
Thus it appears that scotoma awareness training and eye movement practice with dynamic targets can improve the potential of residual vision in individuals with CFL.
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