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Francisco Costela, Stephanie M Reeves, Russell L Woods; Orientation of preferred retinal locus is maintained following changes in simulated scotoma size. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4027.
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© ARVO (1962-2015); The Authors (2016-present)
When central vision loss (CVL) involving loss of the fovea happens, an eccentric retinal location is usually adopted, called the preferred retinal locus (PRL). We do not know what happens to the PRL when the lesion expands, as there is a lack of natural history data. Here we present a prospective study that simulated CVL by training people with normal vision (NV) to develop a PRL with a state-of-the-art, gaze-contingent, visual display. We hypothesized that: (1) Subjects would develop and maintain a robust PRL, as first described by Kwon et al. (2013); (2) Subjects would maintain the orientation of the PRL (theta in polar coordinates) in response to increasing and decreasing scotoma sizes; and (3) Fixational stability and oculomotor control (OMR) would improve throughout the experiment.
Nine subjects with NV (aged 22 to 29 years) were trained to develop a PRL in three phases (Exposure, Train, Refine), during which fixational stability was measured with a 4-degree black scotoma with feathered edges. In the fourth and final phase (Main), subjects were exposed to varying scotoma sizes, which ranged from 4 degrees to 24 degrees. In each phase, subjects were required to either make a saccade, a smooth pursuit eye movement, or fixate at the stimulus (a 500 ms noise circular mask). The experimenter moved on to the next phase when the subject’s PRL was within one degree on three successive blocks (~20 minutes per block). Fixation stability was measured for each fixation trial for each participant by calculating the bivariate contour ellipse area (BCEA) of the fixation points (after removing saccades). OMR was defined as the first landing point of the saccade in response to an instantaneous shift of fixation target and was measured by BCEA.
Subjects were able to develop and maintain a robust PRL in response to simulated CVL. Further, they maintained the orientation of the PRL as the simulated scotoma size varied (0.5 deg theta deviation on average; [0.03-1.20 deg]). Our PRL training induced an asymptotic reduction in both fixation stability and OMR quality (smaller BCEA). OMR improvement took longer to stabilize.
Our PRL development training with NV confirms that the PRL adapts quickly to changes in scotoma size maintaining the orientation of the PRL. These findings may help develop new methods for PRL training to help people with CVL.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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