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L. Jiang, X. Zhou, X. Wu, R. Lu, J. Qu; The Effect of Ambient Illuminance and Its Timing on the Ocular Growth and Refractive Development in C57BL/6 Mice. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3925.
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It is known that refractive errors can be induced in chicks by continuous exposure to light, but the effects of continuous light on refractive development and eye growth in mice have not been studied in detail.
Two groups of mice were used, each split into 3 subgroups of 20-30 animals. In the first group, the total amount of photons was kept similar but light was delivered in different patterns: either 18/6 hour light/dark cycle ("L/D") with the lowest ambient illuminance (167 lux) or 12/12 L/D with intermediate illuminance (250 lux) or 6/18 L/D with the highest illuminance (500 lux). The second group was kept under a 12/12 L/D, but with different levels of ambient illuminance of 125 lux, 250 lux and 375 lux, respectively. Total treatment duration was 16 days from day 12 to 28. Mice that were kept under 12/12 L/D at 250 lux from day 12 to 28 served as controls. Refraction development was followed by automated eccentric infrared photoretinoscopy and corneal radius of curvature (CRC) was measured by a modified keratometery. Ocular dimensions were measured by optical coherence tomography (OCT) with focal plane advancement.
In the first group, even though the total number of photons was kept similar, the sub-group exposed to the longest light cycles developed relative myopia, compared to other two subgroups (-0.95±7.28D in 18/6 L/D, +8.34±5.00D in 12/12 and +7.00±5.39D in 6/18 (p<0.001, ANOVA). Unexpectedly, no differences were found in axial lengths (2.91 mm in 18/6 L/D, versus 2.96 mm in 12/12 L/D and 2.93 mm in 6/18 L/D). In the second group, refractive errors were similar among the three subgroups (+3.87±4.19D, +2.29±4.92D, +3.60±4.36D at 125 lux, 250 lux and 375 lux) and no differences were found in ocular dimensions.
Prolonged exposure to continuous light caused a relative myopic shift in C57BL/6 mice without detectable ocular elongation. In the group kept under 12/12 L/D cycle, no effect of light intensity was found within the narrow range of 125 to 375 lux. Histological examination may reveal whether the shift into myopia was due to retinal degeneration and thining, and perhaps changes in the reflectivity of the fundus - a factor that may affect infrared photorefraction.
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