Abstract
Purpose :
Choroidal thinning is assumed to predict future myopia development. Previously, it was shown that chicks exposed to light flickering at 2 Hz got a thinner choroid but a hyperopic change in refraction. We used two flicker frequencies and measured the time course of choroidal thickness (ChT) changes and eye growth changes to find out whether the predictive power of ChT changes varies with the duration of treatment, and at which time it is valid. ChT and eye growth changes were correlated with the expression level of established markers for altered eye growth to test whether they reflect these temporal phases.
Methods :
13-day old chickens were exposed to continuously flickering RGB light (with light emitting diodes of 635 nm, 525 nm and 470 nm, 240 lux) at 2 Hz, 10 Hz, or no flicker every day for 6 days. ChT was measured using optical coherence tomography (OCT) at 9 am, 1 pm, and 5 pm every second day. On the other days, the refractive state of the eyes (photorefraction) and the biometry of the eye (ultrasound) were measured. At day 7, all eyes were enucleated, and the vitreous, retina, and choroid were collected. Retinal expressions of Egr1, BMP2, and OPN4 were quantified with real-time PCR.
Results :
For both flicker exposures, a time-dependent tendency of choroidal thinning was found. The change in ChT (5 pm: baseline ChT – ChT at day 6) was significantly higher in the 10 Hz flicker group compared to the controls (-49.2 µm vs. -18.2 µm; p<0.05, Two-way ANOVA). The 2 Hz flicker had no significant effect on axial eye growth, while the 10 Hz flicker reduced the rate of eye growth compared to the control animals by 31% (p<0.05). The refractive state was the same in all groups. After 2 Hz flicker exposure, the expression level of Egr1 was higher and that of BMP2 was lower than in the control condition (p = 0.08, and p = 0.06, respectively, One-way ANOVA). After 10 Hz treatment, the expression of BMP2 was lower than control (p = 0.09), while that of OPN4 showed no difference.
Conclusions :
When exposed to light flicker at 10 Hz, the choroid of the chicks became thinner, but eye growth was lower after 6 days of exposure. The measured retinal candidate genes did not correlate with the changes in eye length growth. Further studies in the choroid and retina are necessary to investigate the processes and gene expression changes involved in the decoupling of choroidal thickness change and eye length growth.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.