Potential Inhibitory Effect of LED-Sourced Red Light Therapy on Ocular Growth in Normal and Myopic Chicks

Repeated low-level red light (RLRL) has been reported to control myopia progression clinically. Given safety concerns with laser sources, light-emitting diodes (LED)-sourced red light represents a promising alternative. This study investigated the effects of LED-sourced red light (RL) on cellular response in vitro and ocular growth in normal and lens-induced myopic chicks. In vitro, the mouse photoreceptor 661W cell line was exposed to 625 and 664 nm LED-sourced RL (3 min, twice daily) for 3 days, and cytochrome c oxidase (CCO) activity and cell viability were assessed. In vivo, chicks were randomly assigned to normal visual conditions or monocular -5D lens-induced myopia (LIM). Treatment groups received 664 nm LED-sourced RL (30 min, twice daily) at low, moderate, or high intensities for 10 days. In vitro, LED-sourced RL at 664 nm more effectively activated CCO and enhanced cell viability in 661W cells than RL at 625 nm and white light. In vivo, low-intensity RL exposure of 10 days significantly inhibited vitreous chamber depth (VCD) and axial length (AL) elongation compared to the normal light group (p < 0.05) in normally growing chicks but showed no significant effect in LIM eyes. By contrast, moderate- and high-intensity RL exposure for 10 days attenuated myopia progression in LIM eyes, as reflected by slower VCD and AL elongation and less myopic shift, compared to the normal light group (all p < 0.05). Notably, high-intensity RL also protected the untouched fellow eyes of the LIM chick models against myopic shift and excessive elongation. LED-sourced RL at 664 nm was effective in activating CCO, reducing apoptosis, and promoting cell viability. In chick models, it can also inhibit ocular growth in both normally growing and -5D lens-induced myopic chicks.