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R. S. Ashby, A. Ohlendorf, F. Schaeffel; The Effect of Ambient Illuminance on the Development of Deprivation Myopia in Chicks. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1615.
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Recent epidemiological studies have shown that children who spend a higher proportion of time outdoors are less likely to develop myopia. We have investigated whether light levels are the relevant factor in the development of myopia.
Paradigm 1: chicks were form-deprived for 5 days, with the translucent diffusers removed daily for 15 min under one of three lighting conditions: normal lab lighting (500 lux), daylight (30,000 lux), or intense lab lights (25,000 lux). Paradigm 2: continuously form-deprived chicks were raised for four days under one of three lighting conditions; low lighting (50 lux), normal lab lighting (500 lux), or under intense lab lights (25,000 lux). Group sizes were 9 chicks. Axial length and refraction were measured at the commencement and cessation of treatment.
Chicks which had their diffusers removed for 15min in the sun had significantly shorter eyes (8.81±0.04mm) and a less myopic refraction (-1.1±1.2D) than chicks which were kept under normal lab light levels (9.00±0.05mm, -6.3±1.1D; p<0.001), or continuously form-deprived (9.18±0.16mm, -12.0±1.3D; p<0.001). Similarly, if the diffusers were removed under intense lab lights, the chicks developed shorter eyes (8.83±0.04mm; p<0.01) and a less myopic refraction (-3.3±0.6D; p<0.01) compared to those chicks which had their diffusers removed under normal light levels or continuously form-deprived. Continuously form-deprived chicks reared under high light levels also had shorter eyes (8.54±0.02mm; p<0.001) and a less myopic refraction (+0.04±0.7D; p<0.05) compared to those chicks reared under normal light levels (8.72±0.05mm, -3.5±1.2D). Continuously form-deprived chicks reared under low lighting developed similar levels of myopia to those reared under normal lighting (p=0.57).
Exposing chicks to high light levels, either sunlight or intense lab lights, retards the development of experimental myopia. These results, in conjunction with recent epidemiological findings, suggest that daily exposure to high light levels may have a protective effect against the development of myopia.
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