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Tiffany Arango, Joella Martire, Nicole C Ross, Peter J. Bex; Oculomotor behavior in monocular versus binocular gaze-contingent scotomas. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2165.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with bilateral central vision loss often adopt a preferred retinal location (PRL) in the absence of functional foveae. Fixation stability as quantified by the bivariate contour ellipse area (BCEA) of PRL gaze positions is correlated with functional performance and used as a clinical endpoint. Fixation stability is typically measured under monocular viewing. Little is known about the properties of the PRL under binocular asymmetric scotomas. We explored PRL location and fixation stability under monocular and binocular viewing conditions using simulated independent gaze-contingent scotomas in normally-sighted observers.
Normally-sighted participants completed 3 tasks with monocular (n=12) and binocular (n=12) gaze-contingent pink noise scotomas (0.5, 1, 2 deg radius). Scotomas were updated at 120Hz refresh rate based on a 500Hz eye tracker. For binocular scotomas, the scotoma size and location in each eye was independently controlled with active shutter glasses in 3 symmetric and 3 asymmetric combinations. Participants fixated at a dot at nine locations (8X8 deg grid), and performed a contrast detection task and a word identification task at 2 locations. Outcomes were fixation stability (BCEA, 68%) and PRL location.
BCEA varied as a function of gaze posture in the dot fixation task under both binocular (p<.0001) and monocular (p=.03) viewing conditions. BCEA increased with scotoma size in the monocular (p=0.08), but not in the binocular condition. There was no effect of scotoma size or symmetry on BCEA or PRL location in monocular or binocular viewing for the contrast task. Under monocular viewing for the word recognition task, BCEA increased with scotoma size (p=.01). There was a significant interaction between testing location and scotoma size (p=.04): PRLs were closer to target with the largest scotoma. PRLs were closer to the target in monocular than binocular conditions (p=.04).
For simulated scotomas, estimates of PRL location and stability depend on gaze direction, scotoma size and viewing condition. For a simple fixation task, location influenced fixation stability more than scotoma characteristics. Simulated monocular gaze contingent scotomas capture some, but not all of the oculomotor characteristics observed in patients. The nuanced differences in oculomotor control with monocular compared to binocular scotomas emphasize the need to measure visual function binocularly.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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