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Yuval Cohen, Rafael Iribarren, Arieh Sorin Solomon, Richard A Stone; Environmental Alteration of Crystalline Lens Power by Light During Refractive Development in Chicks.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2730.
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To examine the alteration of crystalline lens power during refractive development of chicks reared under different light intensities, including low ambient illuminance myopia .
Chicks were reared with unrestricted vision under fluorescent lights at three illuminance levels (high:10,000 lux, medium: 500 lux, low: 50 lux) with a 12:12h light:dark cycle for 90 days. Under anesthesia, the eyes were refracted with vercuronium cycloplegia and measured with keratometry and ultrasound. Crystalline lens power was calculated with Bennett’s formula using spherical equivalent, keratometry, anterior chamber depth, lens thickness and axial length measured on days 10 (the baseline), 30, 60 and 90. The alteration in lens power was compared between light intensity groups. Analysis used paired t-test and one-way ANOVA.
Refraction and ultrasound measurements were dependent on light intensity. The lower the intensity of light, the faster the emmetropization and the longer the axial length. The baseline crystalline lens power was 112 diopters (D), and declined to 64-66 D in all cohort on day 30 (p=0.4). Sixty days post-hatching, axial elongation was accompanied by a fast decline in lens power toward 55.9 D, 54.3 D, 50.1 D for the high, medium and low illuminance groups, respectively (p<0.001). Thereafter, axial elongation continued in all groups, while the decline in crystalline lens power for the low illuminance group stopped (p = 0.72) but not for high and medium illuminance groups (p<0.001).
During the 90 days post-hatching, light intensity influenced the developmental changes in crystalline lens power. At the later interval, the lens power stabilized at low, but not higher light intensity groups. The development of low ambient intensity myopia in chicks, is attributable to both axial elongation and also to the early stabilization of crystalline lens power.
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