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Y. Cohen, M. Belkin, I. Avni, U. Polat; Light Intensity Modulates Corneal Power as Well as Refraction in Chick's Eye . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1980.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the effect of light intensity on refractive parameters of chick’s eyes reared under continuous light with both eyes open Methods: Thirty–eight chicks reared under 24 hours lighting at three different light intensities, 10000 (N=13), 500 (N=12) and 50 (N=13) lx. The eyes of the chicks underwent repeated retinoscopy and keratometry, as well as axial length, vitreous chamber depth, central corneal thickness and corneal diameter measurements. Results: Light intensity correlates with refraction (Pearson, R=0.73, P=0.0001) and with corneal refractive power (R= –0.615, 0.0001) of developing chicks. At the day 90 post hatching, light intensity exposure of 10000, 500, 50 lx, resulted in hyperopia of +11.97±3.7 (mean±SD), +7.9±4.08 and +0.63±3.61 respectively, while corneal power under those intensities were 46.10±3.62, 49.72±4.16, 56.88±4.92 diopters respectively. Corneal thickness at 10000 lx, 500 lx, 50 lx was 227.6±10.19, 236±15.1 and 239±11.1, while significance was found between the lowest and highest intensity (P=0.0001). Axial length did not significantly differ between the groups, however the vitreous chamber was deeper in the in 10000 lx group than 50 lx, 10.91±1.08 and 10.23±0.94 respectively though at 500 lx vitreous chamber depth was10.2±0.69, which is in the range of the highest intensity Conclusions: Corneal curvature, corneal thickness and ocular refraction are influenced by the intensity of continuous light exposure, the higher the intensity, the more severe the corneal flattening and the hyperopia. Continuous light was previously shown to cause sever corneal flattening and hyperopia in chicks, however, here we show that continuous low intensity illumination results in emmetropia. Light intensity and duration of light exposure during early life of chicks modulates their refractive power of their eyes by modifying mainly the anterior segment dimensions.
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