Effects of Morning or Evening Narrow-band Blue Light on the Compensation to Lens-Induced Hyperopic Defocus in Chicks

Exposure to blue light before bedtime is purported to be deleterious to various aspects of human health. In chicks, blue evening light stimulated ocular growth, suggesting a role in myopia development. To further investigate this hypothesis, we asked if brief blue light altered the compensatory responses to hyperopic defocus.Previous work showed that several hours evening exposure to blue light stimulated ocular growth in chicks, but morning exposure was only effective at a lower illuminance. By contrast, rearing in blue light is inhibited ocular growth in untreated eyes and eyes exposed to form deprivation or defocus. We studied the effects of brief exposures to blue light on the compensation to hyperopic defocus.Chicks wore monocular negative lenses (-10D) starting at age 10d. They were subsequently exposed to blue light (460 nm) for 4 h in the morning or evening for 8-9 days ("dim": 200 lux: morning n = 9, evening n = 11; "bright": 600 lux: morning n = 8, evening n = 20); controls wore lenses in white light (n = 14). Ultrasonography was done on days 1, 5, 8 and 9 for "evening" groups, and days 1, 6 and 8 for "morning". All data are reported as interocular differences (experimental minus fellow eyes). Refractions were measured on the last day.For evening exposure, dim blue light enhanced the axial compensation at all times (change in axial length: d6: 465 vs 329 μm/9d, ANOVA P.001, P = .03; d9: 603 vs 416 μm/9d, ANOVA p.001; P.05). Bright blue light had a transient inhibitory effect (day 5: 160 μm vs 329 μm; P.005). Refractive errors were consistent with axial growth, with "dim" causing more myopia than "bright" (-9.4 D vs -4.7 D; P.05). Morning blue light had no significant effect.We speculate that these findings reflect a complex interaction between illuminance, defocus and time of day.