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John T. Siegwart, Jr., Alexander H. Ward, Thomas T. Norton; Moderately Elevated Fluorescent Light Levels Slow Form Deprivation and Minus Lens-Induced Myopia Development in Tree Shrews. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3457.
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© ARVO (1962-2015); The Authors (2016-present)
Children who spend more time outdoors have a lower prevalence of myopia (Rose et al., Ophthalmol. 2008) and slower myopic progression (Parssinen and Lyyra, IOVS, 1993). We examined whether elevated light levels (ELL), produced with fluorescent bulbs, slow the development of form deprivation myopia (FDM) and minus lens-induced myopia (LIM) in tree shrews (small diurnal mammals closely related to primates).
Juvenile tree shrews wore a monocular diffuser to produce FDM (n=4) or a –5D lens to produce LIM (n=5) starting at 24 days of visual experience. During treatment, the animals were exposed to ~16,000 lux for ~7.75 hours per day (~9:15 AM - 5 PM) produced with an array of compact fluorescent bulbs. The refractive changes in the FDM and LIM animals were compared to animals from previous studies (FDM, n=6; LIM, n=6) that were treated in standard light levels of 500 - 1000 lux.
After 11 days of treatment, ELL reduced FDM (treated-control eye) by 44% (–3.6 ± 0.1 D vs. –6.4 ± 0.7 D) and LIM by 39% (–2.9 ± 0.4 D vs. –4.8 ± 0.3 D) (figure). Control-eye refractions remained hyperopic compared with standard lighting control eyes. When ELL stopped and form deprivation continued, the myopia progression rate increased to parallel that of standard light-treated animals but did not "rebound", suggesting a permanent saving from the reduced rate during ELL. Two LIM animals continued lens wear and ELL and fully compensated for the –5 D lens after 16 and 23 days.
Moderately elevated light levels, comparable to those in the shade on a sunny day, slow the development of FDM and LIM in tree shrews. These findings are consistent with reports that ELL reduces FDM in chicks and macaque monkeys (Ashby et al., IOVS 2009; Smith et al., ARVO E-Abstract 3922, 2011) and LIM in chicks (Ashby & Schaeffel, IOVS 2010). ELL, from fluorescent bulbs that emit minimal UV radiation, may become a useful tool to slow the progression of environmentally-induced myopia in children. The minimal UV in the ELL is consistent with a previous finding that vitamin D supplementation did not reduce FDM or LIM in tree shrews (Siegwart et al., ARVO E-Abstract 6298, 2011), and suggests that the effect is not due to a light-induced increase in vitamin D levels.
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