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Marita P Feldkaemper, Sandra Bernhard-Kurz, Frank Schaeffel; Effects of different light exposure paradigms before myopia is induced. Invest. Ophthalmol. Vis. Sci. 2018;59(9):684. doi: https://doi.org/.
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The time children spent outdoors between ages 3 to 8.5 year was found inversely associated with incidence of myopia in later childhood (Shah et al., 2017). A central question is how the retina could “memorize” previous bright light exposure that later seems to delay the onset of myopia. We have tried to simulate this condition experimentally in young chickens. In addition we tested the effects of different light sources on the development of deprivation myopia.
Exp. 1: Four days old chicks were either kept under 300 lux (control group) or were exposed to intermittent episodes of bright light (1:1 min cycles, 10000 lux:300 lux, 10h/day). After 5 days of exposure, chicks were returned to 300 lux and one eye of each chick was covered with a diffuser. The experiment was repeated 3 times. Experiment 2: 7 days old chicks were unilaterally treated with a diffuser and either kept under 300 lux, or 20000 lux (generated by white LEDs; 15700 lm, 6500 K), or 7000 lux (quartz-halogen lamps, 33000 lm, 2900 K). Refractive state and ocular dimensions were measured in all cases.
Exp. 1: Intermittent episodes of bright light at early ages reduced the amount of induced deprivation myopia at older ages in only one of the three experimental groups. In this experiment, chickens kept under bright light were slightly more hyperopic than the control group (2.60 ± 0.17 D vs 2.04 ± 0.15 D, unpaired t-test, p = 0.026). Subsequently, they also developed significantly less deprivation myopia (DM) (f(0.82) = 9.87, p < 0.01). Exp. 2: High light levels generated by quartz-halogens bulbs significantly reduced the amount of experimentally induced DM (ANOVA: p<0.05), whereas cool white light LED lamps had no protective effect.
The long-term effects of bright light exposure at early ages were variable among groups. Data from one group suggest that the puzzling “memory effect”, recording the information about previous bright light exposure, is represented by more hyperopic refractions at the time when deprivation myopia was induced. In these chicks, development of DM was delayed and reduced. Extrapolated to children, it would be important to find out whether more outdoor exposure results in a more hyperopic baseline refraction before myopia develops at school. High power white LEDs with a peak emission around 460 nm were less effective to inhibit myopia than quartz-halogen lamps with a more sun-like spectrum.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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