Abstract
Purpose :
S-cone isolating visual acuity (sVA) is constrained by the S-cone sub-mosaic. Previous studies relating them have compared acuity from human subjects against the S-cone topography measured in histology, leading to mixed conclusions, potentially due to individual differences in S-cone density. The present study examined sVA in subjects with spectrally classified cone mosaics to test how the grain of the S-cone sub-mosaic limits resolution.
Methods :
Four cyclopleged subjects participated in an sVA task. Two of these subjects had their cones classified via adaptive optics (AO)-OCT based optoretinography at 1.5°, 4°, and 10° nasal eccentricity. The sVA task was performed at the same locations. Subjects adapted to light that appeared yellow (CIE (x,y) : 0.451, 0.516; 200 cd/m2) for two minutes. sVA was then measured using a Tumbling ‘E’ task that showed blue (CIE (x,y) : 0.16, 0.044; 0.66 cd/m2) letters on the same yellow background, with an S-cone contrast of 0.93 (L/M-cone contrasts <0.01). The stimuli appeared on a DMD projector coupled into an AOSLO. High-resolution AOSLO videos were recorded simultaneously with stimulus presentation, to help guide stimulus delivery to the spectrally classified retinal area.
Results :
In agreement with literature, the measured mean foveal sVA was 20/156±33. sVA worsened with increasing eccentricity, though at a faster rate than observed previously. In aggregate, sVA at 1.5°, 4°, and 10° was 20/156±28, 20/232±32, and 20/463±115 respectively. For the two subjects with classified mosaics, sVA at all eccentricities was worse than predicted by the Nyquist limit, as defined by their measured S-cone spacing. The mean Nyquist limit, converted to Snellen acuity, for 1.5°, 4°, and 10° was 20/87±7, 20/135±25 and 20/143±24 respectively. Despite variations in their S-cone density and sVA, the ratio of measured sVA and the Nyquist limit was remarkably consistent between the two subjects at the different eccentricities; 1.6±0.12, 1.7±0.09 and 2.6±0.003 for 1.5°, 4°, and 10° respectively.
Conclusions :
S-cone isolating letter acuity follows a coarser grain than that defined by the Nyquist sampling of the S-cones. Instead, acuity is in good concordance with the Nyquist limit imposed by the small bistratified retinal ganglion cells. The striking consistency of the sampling factor between subjects suggests a unified pooling mechanism, based on inputs from multiple S-cones.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.