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Brian Sullivan, Laura Renninger; Comparing the fixational and functional preferred retinal locus. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5039.
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Individuals with central vision loss (CVL) may adopt a preferred retinal locus (PRL) to eccentrically view stimuli in peripheral retina. PRLs are often defined by measuring the location and extent of peripheral retinal subtended by a small fixation stimulus viewed monocularly with the head stabilized. It is not known if this ‘fixational’ PRL is representative of situations where binocular vision and head movements are allowed, or when stimulus properties are varied.
Monocular visual fields were recording by having subjects detect small suprathreshold stimuli using a scanning laser ophthalmoscope (SLO). Fixational PRLs were measured by having subjects fixate a stimulus for 10s and fitting a bivariate contour ellipse to this data. Using a similar methodology, a second setup using a binocular eye tracker, chin rest and monitor was used to record monocular and binocular visual fields and fixational PRLs. Subjects then participated in a reaching task where their functional PRLs could be evaluated and compared to the fixational PRLs described above. Subjects performed unspeeded reaches to targets presented on a LCD touch screen at a one of eight of positions presented at three eccentricities (5,10 and 15°). Trials were blocked so that subject made reaches with or without head movements, monocularly and binocularly. ‘Functional’ PRLs were measured by using the location of the reach target in the visual field at the reach endpoint.
We have established means to measure monocular visual fields in the SLO and on a computer monitor, with reasonable agreement. Additionally, binocular visual fields may be predicted from the monocular SLO data and compared to measured binocular fields assessed with the eye tracker setup. We present fixational and functional PRL data, including location and extent, using the bivariate contour ellipse area. Preliminary results give evidence that the fixational PRL is not always representative of the functional PRL. Subject reach duration and accuracy data are also presented.
Although an ongoing study, our data thus far suggest that the PRL is flexible under task changing stimulus conditions during a reaching task. Further study is needed to better delineate the circumstances in which this flexibility occurs.
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