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E. A. Rossi, K. Grieve, A. Roorda; Visual Acuity and the Photoreceptor Mosaic. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3175.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the relationship between letter acuity and photoreceptor spacing for adaptive optics corrected stimuli.
The adaptive optics scanning laser ophthalmoscope (AOSLO) was used to project high contrast AO-corrected stimulus onto the retina of three observers. Acuity was measured using a four alternative forced choice tumbling E test. The threshold (82.5% correct) was determined using QUEST. Acuities were measured in the fovea and at the following temporal eccentricities: 0.5, 1, 1.5, and 2-degrees.
Imaging revealed that although all subjects used the same fixation target, there were small differences between the intended and actual test locations. The photoreceptor mosaic was unresolved at the fovea for all observers and at ~0.5 degrees for two observers. The mosaic was clearly resolved at all other eccentricities. Photoreceptor line spacing was determined using an FFT-based method. Minimum angle of resolution (MAR) increased monotonically as distance from the foveola increased. The graph plots the difference between line spacing and MAR as a function of eccentricity. If AO-corrected letter acuity away from the foveola was determined by photoreceptor spacing, then the lines in the graph would be flat at y=0. The downward slope indicates that MAR increases faster than the photoreceptor line spacing.
AO-corrected letter acuity tasks just off the foveola are worse than predicted based upon the photoreceptor spacing of the cone mosaic.
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