Abstract
Purpose :
While “day” exposure to blue light appears important for emmetropization in animal models, and for inhibiting myopia in children, in chicks, exposure in the evening results in growth stimulation (Nickla et al., 2022). While most hypotheses implicate the circadian system for evening blue light effects, questions remain regarding the contribution of the ipRGCs, and whether the crucial variable is blue light per se.
Methods :
All stimuli are given from ZT8-ZT12 for 9 days. High frequency ultrasound measured ocular biometry. I. Is there a “blue light dose-response” for white light? White light (600 lux) with varying amounts of blue were tested: Low (n=8), mid (n=8) and high (n=8). II. Is it only “blue”? We tested “Yellow” (n=15) (700 lux; 490-650 nm) and “Red” light (n=13) (700 lux; 630 +/-12 nm). Controls were in “flat white” light (n=8). III. Are the ipRGCs involved? We used silent substitution to preferentially stimulate melanopsin (n=16). Temporal illuminance contrast (27%) was created with 7 primary LEDs (Ledmotive) flickered at 0.033 Hz. (Spitschan & Woelders, 2018). To control for temporal effects, we tested white light at 0.033 Hz using the same illuminances (n=16).
Results :
I. There was a “dose response” with increasing blue resulting in increasing eye growth (749, 803, 892 µm/9d; ANOVA p<0.0001; low and mid vs. high, p<0.01). II. Both evening yellow and red conditions increased eye growth relative to white controls (954 µm and 914 µm vs 782 µm/9d, ANOVA p<0.01; post hoc Bonferroni p<0.01). Choroid thickening was seen in the “red” condition (22 µm vs -26 µm; p<0.05), and the choroidal rhythm was abolished in “yellow”. III. Our “melanopsin” condition stimulated growth relative to the “steady flat white” control (861 vs 782 µm/9d; p<0.05), however, “white flicker control” resulted in a similar stimulation (894 µm/9d). The “melanopsin” condition resulted in a phase-delay in the choroidal rhythm, supporting an effect on the circadian system.
Conclusions :
Evening blue light may impair emmetropization in a dose-dependent manner via melanopsin stimulation, but contributions from other cones are likely. A signal from LCA may promote growth in the evening “red”/"yellow" conditions as it does in daytime “red”/"yellow" rearing. Evening light exposure to altered spectra promotes eye growth, but whether the effect is due to disruption of LCA signals, circadian influences or both remains unclear.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.