Photoreceptor-specific luminance modulated flicker thresholds in young children

Abstract

Purpose : Rod/cone photoreceptor flicker sensitivity can help in understanding and quantifying the photoreceptor involvement in hereditary retinal conditions. However, there is a lacuna in the literature with regards to normative database for photoreceptor-specific flicker sensitivity in the younger age group (5-17 years) - the age at which many inherited retinal diseases manifest. This study aimed to quantify flicker sensitivity changes in the age between 5-17 years.

Methods : Forty healthy young children (21M, 19F; Mean (± SD) age: 11.20 ± 3.5 years) participated in the study after obtaining written consent from their parents/guardian. All of them had visual acuity of at least 20/25 (logMAR: 0.1) in the good eye. The mean (± SD) spherical equivalent was -0.21 ± 0.5 D. Rod and the cone-specific stimulus was custom built by varying stimulus frequency (5 Hz (rod) Vs 15 Hz (cone)), light level (5 cd/m² Vs 24 cd/m²), size, chromaticity coordinates [(0.58,0.46) Vs (0.18,0.089)]. Flicker modulation thresholds were measured at the centre and 4 different locations (45^o, 135^o, -45^o, -135^o) at 5^o retinal eccentricity using a 2-down 1-up adaptive staircase procedure. The average of the last 6 reversals was taken as the threshold (1/sensitivity). A small subset of individuals (n=10) underwent repeated testing to measure the intrasubject variability in a given session.

Results : The mean (±SD) central and parafoveal cone flicker threshold was 5.66% (1.96) and 4.53% (1.04) respectively. The average central and parafoveal rod flicker threshold was 7.35% (1.89) and 5.62% (1.01) respectively. Central and parafoveal cone flicker thresholds decreased with increasing age (central, Pearson correlation, r=-0.39; p=0.01; parafovea: r=-0.33, p=0.04). However, rod flicker thresholds did not show a significant correlation with age (central, r=-0.29 p=0.07; parafovea: r=-0.18, p=0.26). The coefficient of repeatability (CoR) for rod and cone FMT ranged between 1 -2 %.

Conclusions : Flicker sensitivity in young children improves with increasing age and seems to reach adult levels by age of 14 years. This normative data is useful to compare and quantify photoreceptor-specific deficits in juvenile macular degenerations.

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