Evaluating rod photoreceptor mosaic topography in human albinism

Abstract

Purpose : It has been reported that some mammals with albinism have a 25-30% reduction in rod photoreceptor numbers.¹ While prior studies have demonstrated that cone mosaic topography in human albinism overlaps with that in individuals with normal vision, no such studies on the rod mosaic exist. Here we examined the rod photoreceptor mosaic in individuals with albinism using adaptive optics scanning light ophthalmoscopy (AOSLO).

Methods : A total of 10 individuals (7 females, 3 males; age range = 16-51 years) with likely (n=5) or confirmed (n=5) albinism and 12 ROIs from individuals with normal vision (6 individuals, 5 females, 1 male; age-range= 16-67 years) were included. Individuals were imaged with confocal and split-detection AOSLO, and 30 regions of interest (ROIs) from the 10 individuals with albinism were analyzed (ranging in retinal location from 4.56° to 12.20°). A previously described “spacing-derived” method for estimating rod photoreceptor density and rod:cone ratio was used.² This method utilizes the total number of cones and average cone inner segment area from the split-detection images, along with rod spacing estimates from the confocal image (with the cones masked).

Results : For all 12 control ROIs, rod metrics from the primary grader were within the measurement error derived from repeated measures from 4 graders in a previous study.² In the individuals with albinism, the mean (± stdev) rod density was 95,979 ± 26,477 rods/mm² (range 55,423 to 139,797 rods/mm²). This was similar to previously reported normative values derived using the same method (mean ± stdev = 97,536 ± 15,795; range = 56,973 - 128,262; p=0.71, unpaired t test). The mean (± stdev) rod:cone ratio in albinism was 10.51 ± 5.18 (range 4.07 to 23.17). Again, this was similar to previously reported normative values derived using the same method (mean ± stdev = 10.07 ± 3.43; range = 4.20-19.10; p=0.60, unpaired t test). Our spacing-derived rod metrics (normal and albinism) were generally within normative values from previous ex vivo and in vivo studies.^3,4

Conclusions : Our data are consistent with normal rod photoreceptor topography in human albinism, in contrast to reports in other animals.¹ Future studies are needed to determine the factors influencing the observed individual variation in rod topography in albinism (e.g., genetic subtype, foveal hypoplasia grade, regularity of the underlying cone mosaic).

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.