Abstract
Purpose :
Exposure to evening blue light stimulates eye growth at 200 lux but not at 1000 lux. Because dopamine is thought to be involved in ocular growth inhibition, we asked: (1) Is the diurnal rhythm in retinal dopamine release altered by evening blue light? (2) Is the lack of effect at 1000 lux a result of higher levels of dopamine relative to the lower illuminance? (3) Is the choroid a source of dopamine, and if so, is it rhythmic?
Methods :
Chicks were reared in a 12L/12D cycle (588 lux) with lights on at zeitgeber time (ZT) 0. Experiments began at 7-12 days (d) of age. (1) Chicks were exposed to narrow-band blue light (460 nm; 600 lux) in the evening (ZT8-ZT12) for 7d. Age-matched controls were in white light. Eyes were dissected at 4-hour (h) intervals over 20 h (n=12 at ZT4, ZT8, ZT16, ZT20; n=24 at ZT0 and ZT12), and the vitreous frozen at -80C until processed for dopamine (DA) and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) using HPLC. (2) Chicks were exposed to 4-h evening blue light at 200 or 1000 lux for 8d (n=12 each). Eyes were dissected at ZT6, and the vitreous processed for DA and DOPAC. (3) Choroids of eyes from chicks under white light were dissected at 4-h intervals over 20 h (ZT0 and ZT12, n=17; ZT8, n=8; ZT4, ZT16, ZT20, n=11), and were analyzed for DA, DOPAC and L-DOPA (dopamine precursor). Tyrosinase was measured using ELISA at ZT0 and ZT12 (n=12 each).
Results :
(1) There was a diurnal rhythm in vitreal DOPAC in both control (variance with time: ANOVA p<0.0001) and experimental eyes (ANOVA p<0.01). Evening blue light resulted in lower levels of DOPAC at all times (p<0.001) except ZT0. (2) There was a tendency for vitreal DOPAC to be higher in 1000 lux relative to 200 lux (11.9 vs 9.0 pg/µl; p=0.059). (3) DA, L-DOPA, and DOPAC were all detected in choroid, but only L-DOPA showed a significant variance over time (ANOVA p=0.04); L-DOPA was higher at ZT8 than at ZT0 (post-hoc Bonferroni, p<0.05). By contrast, tyrosinase levels were higher at ZT0 than at ZT12 (27.4 vs 17.2 ng/mg protein; p<0.01).
Conclusions :
Blue evening light reduced the amplitude of the DOPAC rhythm, which may be linked to the ocular growth stimulation. The lack of stimulatory effect at 1000 lux blue light may be due to differences in dopamine metabolism. The choroid may be a source of dopamine; that L-DOPA and tyrosinase vary with time of day suggest a role for dopamine in the diurnal choroidal thickness changes.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.