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D. S. Hammond, C. F. Wildsoet; Emmetropization Responses of Young Chicks Under Uv Illumination. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1731.
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In a previous study using low power lenses, chicks were found not to compensate for imposed defocus under near-ultraviolet (UV) lighting, chosen to isolate the spare UV cone photoreceptors of the chick retina (383nm, 1.5 chick lux; Rohrer et al., 1992). We examined the wavelength and lens power dependence of this effect.
Young chicks were reared from 3 days of age under either 365 or 390nm lighting, both of which isolate UV cones. One eye of each chick was randomly selected to wear a UV transmitting lens, either +20, +10, -10, -20D, with the fellow eye serving as a control. Biometric and refractive data were collected on days 0, 2, 4, 7, 11. The function y= 2x10-7x3- 0.0002x2 + 0.0906x - 11.186, was used transform measured irradiance to chick illuminance (chick lux). The illumination at the cage floor experienced by lens-wearing eyes was 4 and 68 chick lux for the 365 and 390nm conditions respectively, after accounting for the reduced transmittance (56%) of the lenses to the 365nm wavelength.
For the 365nm condition, all lens-wearing eyes exhibited myopic shifts in refraction and increased vitreous chamber depths (means for +20D: 0.814mm; +10D: 0.521mm; -10D: 0.362mm; -20D: 0.464mm), regardless of the sign of imposed defocus, with no change in choroidal thickness. In contrast, for the 390nm condition, chicks exhibited the usual sign-dependent differences in eye growth, the choroids thickening and thinning in response to imposed myopic and hyperopic defocus respectively, with parallel decreases and increases in vitreous chamber depth (means for +20D: -0.449mm; +10D: -0.238mm; -10D: 0.576mm; -20D: 0.792mm), although the -10D treatment group becomes more myopic than required for compensation (-13D).
Provided the illumination is sufficiently high, input from UV cones appears to be sufficient for bi-directional emmetropization in young chicks, although the accuracy of compensation is impaired. Differences in either or both lighting levels and lens material may explain the previously published negative finding.
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