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T. Li, H.C. Howland; The Effects of Monocular Light Deprivation of Chicks on Ocular Development Under Various Illuminative Regimes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3334.
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Our previous experiments have shown that raising young chicks (Gallus Gallus domesticus) in constant light (CL) or constant dark (CD) alters their refractions, corneal radii and their ocular components. The ocular changes under CL can be significantly reduced by covering the pineal gland, eye, or even the fellow eye 12 hours per day. We wished to investigate the effects of constant covering during the chicks' eye development under various illumination conditions.
Newly hatched chicks were raised either under normal lighting (12L/12D), CL or CD conditions. Half of the chicks under each condition were monocularly covered continuously with opaque hoods. Using an infrared keratometer and photorefractor as well as a "A" scan ultrasound, we monitored those aspects of the eye known to be affected CD, namely: corneal radius of curvature, anterior chamber depth, refraction, and vitreous chamber depths at the end of two weeks for all the chicks.
After two weeks of experimental treatments, as expected, chicks in CD and CL conditions developed respectively significant CD or CL effects such as flatter corneas, shallower anterior chambers, deeper vitreous chambers and hyperopic refractions (p<0.0001). Monocularly occluded eyes showed significant myopic refractions in 12L/12D, with a mean refraction of about –10 diopters (p<0.0001). In CL, occluded eyes showed less hyperopia than their fellow eyes (p<0.0001) and no refraction change in CD between occluded eyes and fellow eyes. In addition, compared with fellow eyes, occluded eyes showed significantly deeper vitreous chamber depths and longer axial lengths (p<0.0001) in 12L/12D and CL chicks, but not in CD chicks.
Monocularly occluded eyes show visual deprivation effects, rather than constant dark effects when chicks are raised in a 12L/12D environment. Previous experiments have shown that the occluders do not leak light. Thus the illumination environment of the fellow eye can dramatically influence the development of an occluded eye. Our results indicate that 12L/12D diurnal light inputs to fellow eyes may play an important role in visual deprivation myopia.
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