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Tatiana V. Tkatchenko, Yimin Shen, Andrei V. Tkatchenko; Photopic Visual Input Is Necessary For Emmetropization In Mice. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3449.
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Mice develop higher degrees of both form-deprivation and lens-induced myopia if placed in photopic conditions (constant light). However, it is not clear how constant light effects normal refractive eye development in mice and what role photopic visual input plays in refractive eye development in this species. The purpose of this study was to investigate how different lighting conditions affect refractive eye development and susceptibility to experimental myopia in mice.
Using a high-resolution automated eccentric infrared photorefractor and high-resolution MRI, refractive eye development was compared under regular (12 h light/12 h dark) light, constant light (200 lux) and constant darkness conditions in P21-P67 C57BL/6J mice.
The average refractive errors in the regular-light group were -13.2 ± 2.0 D at P21, -0.5 ± 1.5 D at P32, +0.3 ± 0.9 D at P40, +2.2 ± 0.9 D at P67. The average refractive errors in the constant-light group were -12.5 ± 1.2 D at P21, -1.0 ± 0.9 D at P32, +0.1 ± 0.9 D at P40, +0.2 ± 0.9 D at P67. The average refractive errors in the constant-darkness group were -12.5 ± 2.2 D at P21, +5.2 ± 2.2 D at P32, +8.7 ± 2.3 D at P40, and +11.2 ± 2.1 D at P67. Analysis of variance (ANOVA) revealed that refractive eye development in the regular-light group was significantly different from that in the constant-light group (F(3, 84) = 5.946, P = 0.001). However, the largest differences were observed between the constant-darkness group and two other experimental groups, i.e., regular-light (F(3, 84) = 48.536, P < 0.0001) and constant-light groups (F(3, 90) = 87.229, P < 0.0001). We also found significant differences in the ocular component dimensions in different experimental groups. After 21 days of form deprivation, we detected a myopic shift in refraction in the deprived eyes compared to the control eyes in the constant-light (-12 ± 1.4 D, P = 0.0004) and regular-light (-2.7 ± 0.7 D, P = 0.0001) groups, while no shift in refraction was observed in the constant-darkness group (-0.3 ± 0.5 D, P = 0.1).
Our data indicate that mice, which are raised in the regular light or constant light conditions (hence receive photopic visual input), undergo emmetropization and develop experimental myopia, whereas, animals, which are raised in constant darkness (no photopic visual input), fail to emmetropize or develop experimental myopia. Emmetropization is most efficient under the constant light conditions, i.e., under conditions, which ensure the greatest photopic visual input in mice. Thus, photopic visual input is necessary for emmetropization in mice.
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