The topography of S-cones in the macula establishes the neuronal limitations for coding the color vision’s short-wavelength spectrum. According to the findings, S-cones tile the central human retina with a non-random crystalline arrangement. The conclusion differed from earlier research, most likely due to the small sample size. Adaptive Optics Line-scan OCT and a bleaching stimulus of 660±10 nm were used to classify cones in two patients. At 1.5° and 4° eccentricity over the four meridians, 8 ROIs were categorized per individual. Total and S- cone numbers per ROI ranged from 541-3545 (mean: 1823) to 38-171 (mean: 99). Using the standard Density Recovery Profile approach, researchers assessed S-cone spacing in each ROI (DRP).
For a study, investigators sought to compare with the random arrangement; therefore, they conducted 1000 Monte Carlo (MC) simulations of each ROI, keeping the cone placements but randomizing the S-cone locations inside it. They then measured the radius in units of inter-cone distance where S-cone density was significantly lower than MC distributions, finding low density in a 1-cone radius in 13/16 ROIs (8/8 at 1.5°, P≤.037. 5/8 at 3.5°-4.5°, P≤.002), and up to a 2-cone radius in 12/16 ROIs (7/8 at 1.5°, P≤.002. 5/8 at 3.5°-4.5°, P≤.003). Additional human volunteers, ROIs with larger eccentricity, and classification using a short-wavelength bleach would be used in future investigations. The discoveries had far-reaching consequences for retinal development and color-coding retinal circuitry.