In-vivo cone photoreceptor topography of the normal human foveola

Abstract

Purpose : To quantify cone photoreceptor topography of the normal human foveola in-vivo.

Methods : The foveal centers of both eyes of 29 participants in retinal health (27 ± 7 yrs / 19 female) were imaged with adaptive optics scanning laser ophthalmoscopy (711 or 788 nm center imaging wavelength, 0.85-degree field of view). Cone locations in image montages covering the central ~2 deg of visual angle were marked using custom software. Two-dimensional cone density maps were computed via the Voronoi area of the closest 150 cones to each image pixel. The anatomical center of the foveola, or 0 eccentricity, was defined at the cone density centroid (CDC), i.e. the weighted center of the top 20% cone density contour. Cone density profiles were analyzed as radial averages and in 10-deg sectors around the horizontal and vertical meridians. The absolute and normalized individual and group profiles of the log transformed densities, D_log, were fitted by a three-parameter function of log transformed eccentricity, E: D_log(E_log ) = a*e^(-((E_log-b)/c)²).

Results : Across all participants, cone density at the CDC was between 10,570 and 17,000 cones per deg², dropping to a third at about 1 deg eccentricity, on average. Meridional cone profiles broadly followed a sigmoid, reaching maximum slope at about 11 arcmin eccentricity. Average best fit parameters were a_h = -1.38, b_h = 7.35 and c_h = 1.77 and a_v = -1.7, b_v = 7.72 and c_v = 2.09 for the horizontal and vertical normalized profiles, respectively. Within the central 0.5 deg, vertical profiles were significantly steeper than horizontal profiles (p < 0.01, paired t-test). There was a non-significant trend towards ~2 % higher densities in the temporal compared to nasal foveal sector. All metrics were highly correlated between fellow eyes.

Conclusions : The relative cone photoreceptor density profile was, despite large interindividual differences in absolute numbers, highly similar between individuals. A three-parameter equation of cone density as function of eccentricity was able to model cone density for the central 2 deg retina within 3.3 % and 2.7 % for horizontal and vertical profiles, respectively. Such a model will be useful to investigate normal foveal anatomy and development, for intra- and extrapolation in cases of non-resolved imagery and for benchmarking topographical changes in retinal diseases.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.