Contributed Session III: The limits of resolution in the S-cone pathway.

Abstract

The resolution of the S-cone pathway is first constrained by the density and arrangement of S-cones in the photoreceptor mosaic. Prior work comparing S-cone isolating visual acuity (sVA) to histological estimates of S-cone density has led to mixed conclusions, likely due to inter-individual differences in the S-cone sub-mosaic. We examined sVA in subjects with spectrally classified cone mosaics to test how the grain of the S-cone sub-mosaic limits resolution. Three observers whose cones were previously classified via adaptive optics (AO)-OCT based optoretinography participated in an sVA task at eccentricities ranging from 1.3° to 12.9° spread along all four cardinal meridians. Observers adapted to yellow light [CIE (0.45, 0.51); 200 cd/m2] for two minutes.Then, acuity was measured using a Tumbling 'E' task that showed blue [CIE (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). Simultaneously recorded high-resolution AOSLO videos helped guide stimulus delivery to the spectrally classified retinal area. Measured sVAs were worse than predicted by the calculated S-cone Nyquist limit at all eccentricities, suggesting pooling of information from S-cones. Moreover, this pooling increased with eccentricity. While sVA does not follow the S-cone Nyquist limit, it is in good concordance with the Nyquist limit corresponding to known estimates of the sampling density of small bistratified retinal ganglion cells.