Structural and functional assessment of photoreceptors in healthy individuals

Abstract

Purpose : Establishing the relationship between photoreceptors and visual function in the normal population is crucial for understanding the effects of progression and/or treatment of retinal disease. By using highly sensitive measures of photoreceptor structure and function, we aim to determine if there is a correlation between cone density, rod/cone function, and color vision in a group of healthy individuals.

Methods : Monocular data from ten healthy individuals were examined (6M, 4F, mean age: 29 years, range: 24-36 years). Functional assessment was carried out using Advanced Vision & Optometric Tests (AVOT), and included rapid flicker sensitivity, measured with cone- and rod-enhanced stimuli (at the fovea and in 4 quadrants located at 5 degrees eccentricity), as well as colour vision, measured using the Colour Assessment and Diagnosis (CAD) test. The CAD test yielded both red-green (RG) and yellow-blue (YB) chromatic discrimination thresholds. Photoreceptor structure was assessed using nonconfocal split-detection Adaptive Optics Scanning Light Ophthalmoscopy (AOSLO). Cone density was measured at 0.5, 1 and 5 degrees along the temporal meridian, using 55 x 55 μm regions of interests (ROIs). Three ROIs at each location were quantified twice by two independent graders.

Results : Measurements fell within the normal range for all AVOT and AOSLO assessments (Table 1). Agreement between cone density measurements of the two graders was excellent (intraclass correlation coefficient = 0.988, 95% confidence interval = 0.980-0.993). There were no statistically significant correlations between central cone density (0.5 or 1 degree) and either CAD or foveal cone-mediated thresholds (Pearson, p > 0.05). Nor were there any significant correlations between cone density at 5 degrees and peripheral rod- or cone-mediated thresholds (in the upper and lower temporal quadrants) (Pearson, p > 0.05).

Conclusions : Despite their current use as outcome measures in clinical trials for gene therapy, this is the first time the CAD, rod- and cone-mediated flicker tests and AOSLO have been validated against each other. Our data suggest that, in healthy individuals, natural variation in cone density does not have a significant effect on visual function.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.