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Jenny Lorén Reiniger, Niklas Domdei, Michael Linden, Frank G. Holz, Wolf Maximilian Harmening; Relationship between the foveal photoreceptor mosaic and adaptive optics corrected visual acuity. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1777.
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© ARVO (1962-2015); The Authors (2016-present)
Visual acuity is limited by the eye’s retinal image quality, retinal sampling density of the photoreceptors and post-receptoral visual processing. The contribution of each of those factors in an individual eye is difficult to discern, and earlier estimates rely on population based histological findings. By employing high-resolution retinal imaging and stimulation techniques, we here investigated the relationship between the exact geometry of an individual’s foveal cone mosaic and their performance in visual acuity tasks directly.
Both eyes of seven subjects were imaged with an adaptive optics scanning laser ophthalmoscope (AOSLO). For each eye, the positions of all foveal cones were marked manually in registered and averaged images (150 frames, λ = 840nm) of the central 0.85° field of view. Within this field, cone distribution metrics were evaluated with respect to the preferred retinal locus (PRL) of fixation. Individual PRLs were found from 10s long AOSLO videos during attempted fixation of a 1.5 arcmin square stimulus. Visual acuity thresholds were determined from five consecutive adaptive staircases using AOSLO microstimulation under ocular aberration compensation. Acuity optotypes were dark tumbling E stimuli shown against the imaging raster (λ: 840nm, CM: 60-75%, luminance: 3.4cd/m2).
The complete foveal photoreceptor mosaic, including the smallest cones of the foveola, was resolved and quantitatively analyzed in all subjects. Maximum cone densities were between ~12 000 and 18 000 cones/deg2, corresponding to a theoretical maximum resolution of 0.42 – 0.51 arcmin (Nyquist limit). Tumbling E acuity thresholds were between -0.25 and -0.4 logMAR (0.4 and 0.6 arcmin). Linear correlation analysis revealed similar relationships between visual acuity (logMAR) and photoreceptor density (cones/deg2) at the retinal locus of maximum density (r2=0.59, p=0.04) and the PRL (r2=0.53, p=0.06).
Under optimal viewing conditions, individual visual acuity thresholds match the Nyquist limit of sampling of the cone photoreceptor mosaic at the PRL, while the retinal location of maximum density would have provided a 7% higher sampling limit, on average. This observation supports the hypothesis that the exact location and geometry of the foveal cone mosaic limit resolution, and suggests that post-receptoral processes do not limit maximum resolution more than the receptor mosaic.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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