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T. Li, C. Wahl, H.C. Howland; Age dependent ocular changes of chicks under constant light, and recovery from them, in normal illumination . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4291.
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Purpose: Raising chicks (Gallus Gallus domesticus) in constant light (CL) is known to alter their refractions, corneal radii and the ocular components. We wished to assess the severity of CL effects and the degree of recovery possible at various ages. Methods: Two groups of 12 newly hatched chicks were raised under normal lighting conditions (12 hours light, 12 hours darkness per day (N or 12/12) and under CL for up to 7 weeks of age. Half of the chicks from each condition were switched to the other condition, "N" to "CL" (N–CL) or "CL" to "N" (CL–N) for another 5 weeks. And then the same switches were repeated in the half of chicks left from N or CL groups for another 40 days. Using an infared keratometer and photorefractor as well as a "A" scan ultrasound, we also monitored those aspects of the eye known to be affected or possibly affected by CL, namely: corneal radius of curvature, anterior chamber depth, refraction, lens thickness and vitreous chamber depths at each switching time (7 and 12 wks), and also at the end of the study (17 wks) for all the chicks. Results:At the age of 7 wks, chicks still can develop statistically significant CL effects after they are switched to CL conditions for 5 wks (p<0.05), but, compared with the chicks of the same age raised only in CL, the effects are small. On the other hand, excepting the vitreous chamber depth, the CL effects of the chicks raised in CL for 7 wks could be almost totally reversed after they were switched to the N condition for 7 wks. At the age of 11 wks, the CL effects could not be induced by switching the N chicks to CL for 7 wks. By way of contrast, however, recovery of the CL effects on refraction could still take place by vitreous chamber elongation rather than corneal reshaping after switching 12 wks old CL chickens to the N condition for 6 wks. Conclusions:Ocular development changes in CL conditions are age dependent. After 11 wks, CL no longer affects the development of corneal shape, although the recovery of CL effects on refraction still can be effected by vitreous chamber elongation. These unsymmetrical effects indicate that the cornea loses the ability to reshape itself before that of the posterior segment in chick eyes. Supported by NIH Grant EYO2994 to HCH. None
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