Evening Blue Light Exposure, Ocular Growth Stimulation and Altered Dopamine

Exposure to blue light in the evening stimulates eye growth at 200 but not 1000 lux. We asked whether the diurnal rhythm in retinal dopamine release is altered by evening blue light, whether the lack of effect at 1000 lux is due to higher dopamine, and whether the choroid may be a source of dopamine.

Chicks, on a 12h light-dark cycle with lights on at zeitgeber time 0 (ZT 0), were exposed to narrow-band blue light at 600 lux in the evening (ZT 8-ZT12) for 7d; control subjects were exposed to white light at 588 lux from ZT0 - ZT12. Eyes were dissected at 4-h intervals over 20 h, and the vitreous processed for dopamine (DA) and its metabolite DOPAC using high-performance liquid chromatography (HPLC). We also measured the effects of 200 lux vs 1000 lux blue light illuminances at ZT 6. We looked for dopamine synthesis in choroids of control eyes using HPLC, and measured tyrosinase protein levels using ELISA in eyes exposed to blue evening light.

There was a diurnal variation in vitreal DOPAC in control (ANOVA p < 0.0001) and experimental eyes (ANOVA p < 0.01). Evening blue light resulted in lower DOPAC at all times (p < 0.001) except ZT 0. There was a trend for vitreal DOPAC levels to be higher in 1000 lux relative to 200 lux (11.9 vs 9.0 pg/µl; p = 0.059). DA, L-DOPA, and DOPAC were detected in choroid, but only L-DOPA showed a significant variance over time (ANOVA p = 0.04), being highest at ZT12. Evening blue light decreased tyrosinase levels relative to controls at ZT0 and ZT12.

Blue evening light reduced vitreal DOPAC levels, indicative of reduced retinal dopamine release, suggesting a dopamine-mediated mechanism in the blue-light-induced ocular growth stimulation. Choroidal dopamine may supplement retinal dopamine release in regulating eye growth.