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I. G. Morgan, S. McCarthy, P. Kozulin, P. Megaw; Does Bright Outdoor Light Block the Development of Form-Deprivation Myopia?. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3924.
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Epidemiological evidence suggests that children who spend more time outdoors are less likely to develop myopia. A possible reason for this could be the exposure to higher light intensities typical of outdoor environments during the day, and a higher rate of retinal dopamine release. To investigate this hypothesis we employed the chicken model of experimental myopia.
White leghorn x Australorp chickens were raised under 12:12 light:dark cycle (dark < 1Lux, light = 150 Lux) for the first 7 days post hatching. On the seventh post-hatch day, half the chickens were fitted with diffusers to induce myopia. Six-diffuser fitted chickens and six normal chickens were moved to a cage inside a temperature control glasshouse with a light level averaging 15000 Lux for 6 hours a day for 7 days. Chickens were refracted at the end of the experiment and axial length was measured to determine the amount of eye growth.
Axial length was reduced in normal chickens that were exposed to outdoor light. In birds fitted with diffusers and reared under normal laboratory conditions, axial lengths were significantly longer in the form-deprived eyes than in the contralateral eyes. In birds fitted with diffusers but placed outside for 6 hours a day for 7 days, both experimental and contralateral eyes were shorter than eyes in control birds, but the inter-ocular difference was similar. There was no effect on the development of refractive error.
Despite the inhibition of eye growth in chickens held outside for 6 hours each day, there was no inhibition of the development of form-deprivation myopia. This result may indicate that light exposure is not the critical factor in the protective effect of time spent outdoors. Alternatively, the stimulus to growth provided by form-deprivation may be too strong to be over-ridden by light.
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