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Susana T L Chung, Mehmet N Agaoglu, Christy K Sheehy, Pavan Tiruveedhula, Austin Roorda; Functional impact of fixational eye movements during an orientation discrimination task in people with macular disease. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4303. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
People with macular disease invariably exhibit highly unsteady fixational eye movements (FEMs), characterized by large amplitudes of slow drifts and microsaccades. Are these abnormal FEMs detrimental to vision due to the excessive retinal image motion, or are they helpful in enhancing fine spatial details for people with macular disease? In this study, we examined whether an exaggeration or a reduction in FEMs would lead to better performance for an orientation discrimination task in observers with macular disease.
A sinusoidal grating (1–4 cpd) tilted ±45° from vertical was presented at the preferred retinal locus (2.3–4.8° eccentricity) of four observers with long-standing macular disease, using a custom-built eye-tracking scanning laser ophthalmoscope (TSLO). The TSLO allows simultaneous imaging of the retina while delivering stimulus at a precise retinal location, as well as stabilization of the stimulus on the retina. A range of image stabilization gains was tested such that the image of the grating could be stabilized, unstabilized or moved more or less than the natural FEMs on the retina. Following a 1-s presentation of the grating, observers reported the perceived orientation of the grating (left or right). Only trials with accurately delivered stimulus were analyzed. An offline cross-correlation algorithm (sampling rate 540 Hz) was used to extract the positions of the eye and the image of the grating from which the retinal image motion was calculated. Metrics including fixation stability and image velocity were used to characterize the retinal image motion.
In general, observers’ performance accuracies for identifying the grating orientation varied with the range of metric values non-monotonically. For each observer and most metrics, although accuracy was never the highest at the value corresponding to unstabilized FEMs; it was only slightly lower than at other (usually smaller, corresponding to less retinal image motion) metric values (e.g. 72%-correct [unstabilized] vs. 79%-correct [smaller value] for fixation stability and peak retinal velocity).
Despite their abnormal FEMs, performance for orientation discrimination is close to the best that people with macular disease can attain when viewing the stimulus using their natural FEMs. Reducing the retinal image motion may improve performance for these individuals, but only modestly.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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