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Laura Renninger, Anna Ma-Wyatt, Donald C. Fletcher; The Preferred Retinal Locus Is Not A Pseudo-fovea For Directing Rapid Hand Movements In Age-related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1193.
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There is some debate as to the optimal location of the preferred retinal locus for reading, and there is evidence that more than one PRL may be used for the same or different tasks. In reaching and pointing tasks, subjects without central field loss use the fovea to locate a target, and this eye position signal aids targeting of the point, even when the visual stimulus is turned off during the saccade. In this study, we examine to what degree the PRL in acts like the fovea for target localization in a pointing task.
AMD participants were referred to the study after low vision rehabilitation consultation. Central field loss and PRL location was measured with SLO macular perimetry and CCVFT. In the reaching task, subjects first fixated a central target with the PRL and pressed a button to begin the trial. A high contrast dot appeared at distances ranging from 2°-12° in a block design, in one of eight directions. Subjects were asked to make a rapid point to this target. The reach endpoint was recorded with a touch sensitive LCD and eye movements were tracked
Overall, saccade latencies and reach times were comparable to that found for normal-sighted, age-matched observers, and declines were also observed in endpoint accuracy and precision as a function of target distance. The PRL moved from fixation toward seen targets, indeed acting like a "pseudo-fovea". When the target was unseen (in the scotoma), searching behavior ensued. Unlike saccades and reaches in normals, however, the pattern of movement endpoints were not radially oriented and hypometric. Instead, a positional bias along the PRL-to-fovea axis was evident in which saccade endpoints were shifted away from the fovea, and the reaching endpoints shifted toward the fovea.
Although movement dynamics appear normal, the loss of radial saccade endpoint patterning and the opposing biases in saccade and reach endpoints suggest that recalibration of these motor reference frames is incomplete.
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