Abstract
Purpose :
The topography of S-cones in the macula sets neural constraints for coding the short-wavelength spectrum of color vision. We aimed to characterize topography of S-cones in the central human cone mosaic and to what extent it deviates from a random arrangement.
Methods :
In 2 subjects, cone sub-types were classified via Adaptive Optics Line-scan OCT and a bleaching stimulus of 660±10 nm. Regions of interest (ROIs) were classified at 1.5, ~4, and 10° eccentricity across the 4 cardinal meridians (12 ROIs each). S-cone spacing was quantified in ROIs containing >= 1000 cones using Density Recovery Profile (DRP). DRP measures the density of S-cones at regular intervals within some radius of other S-cones. These were binned by the average nearest-cone distance per ROI, such that DRP was calculated at 1-cone intervals within 18 arcmin. To compare with random arrangement, 1000 Monte Carlo (MC) simulations of each ROI were generated such that cone locations in the mosaic and number of S-cones were maintained, but positions of S-cones within the mosaic were randomized. Crystalline arrangement is indicated by bins at which the DRP for a true S-cone sub-mosaic is significantly lower than the MC distribution.
Results :
Mean and std of total cones classified and quantity S-cones per ROI at each eccentricity were 2374±665, 1211±391, and 700±229 at 1.5°, ~4°, and 10° respectively. Density of S-cones decreased with eccentricity while their percentage increased (density (1/deg.2): [1.5°: 152.9 ± 43.3, ~4°: 74.8±22.3, 10°: 61.1±15.9], percent (%): [1.5°: 5.2±0.5, ~4°: 6.2±1.0, 10°: 8.3±2.0]). DRP was calculated for 14/24 ROIs (8, 5, and 1 ROI(s) at 1.5°, ~4°, 10°, respectively, with bin-widths (arcmin) 1.25±0.16, 1.87±0.17, and 2.25).. A low density of S-cones (p < 0.05) was observed in 13/14 ROIs within a 1-cone [1.5°: 8/8, ~4°: 5/5; 10°: 0/1] and 2-cone [1.5°: 7/8, ~4°: 5/5, 10°:1/1] radius. Beyond a 2-cone radius, the DRP was indistinguishable from random but for exceptions in two 1.5° ROIs (at a 6-cone and 12-cone radius respectively).
Conclusions :
We find that S-cones are arranged with non-random crystallinity in the central human cone mosaic such that they avoid a 2-cone radius of one another. It is unclear whether this crystallinity changes with eccentricity. This finding departs from previous studies, likely due to their limited sampling, and has important implications for retinal development and color-coding retinal circuits.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.