Distribution and morphology of human cone photoreceptors stained with anti‐blue opsin

TLDR

Primate blue cones have been identified only indirectly, leaving their precise distribution and morphology unclear. The authors stained seven whole‑mounted human retinas from six female donors with an affinity‑purified anti‑blue‑opsin antibody, counted cones whose outer segments could be traced to inner segments, and measured their dimensions where cells were vertically aligned. Blue‑opsin labeling showed that only ~7 % of cones within 4 mm of the fovea are blue, that these cones are taller, more cylindrical, and sparsely distributed with a ~100 µm foveal gap, reach densities >2000 cells/mm² at 0.1–0.3 mm eccentricity, and are statistically independent from red/green mosaics—findings consistent with foveal tritanopia and suggesting blue‑cone spacing limits blue‑channel resolution to 20–30°.

Abstract

Abstract Primate cones maximally sensitive to short wavelength light (blue cones) have been previously identified by using indirect methods. We stained 7 wholemounted human retinas obtained from 6 female donors, using an affinity purified antibody to a 19 amino acid peptide sequence at the N‐terminus of blue opsin (Lerea et al., '89: Neuron 3 :367–376), standard PAP immunocytochemistry, and controls. Cones were counted where all outer segments could be traced to inner segments and were measured where cells were well aligned vertically. We find that: (1) 7% of cones within 4 mm of the foveal center are labeled by antiblue opsin; (2) compared to neighboring red/green cones, blue cone inner segments are 10% taller, have a larger cross‐sectional diameter near the junction with the outer segment, and a smaller diameter near the external limiting membrane, resulting in a more cylindrical shape, (3) foveal blue cones are sparse, irregularly spaced, and missing in a zone about 100 μm (0.35°) in diameter near the site of peak cone density, (4) the highest densities of blue cones (> 2,000 cells/mm 2 ) are found in a ring at 0.1–0.3 mm eccentricity, and (5) the shortest distances between neighboring cones are between blue and red/green cones, and the blue and red/green mosaics are statistically independent. These findings are consistent with psychophysical reports of foveal tritanopia and maximum sensitivity to blue light at 1° eccentricity. Blue cone spacing may limit resolution of the blue channel out to 20–30° eccentricity. The blue and red/green mosaics appear to be formed by separate processes.