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A.L. Roberts, X. Zhu, J. Wallman; Lens-compensation under Dim Illumination: Differential Effects on Choroidal Thickness and Ocular Elongation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1981.
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Purpose: When eyes wear positive or negative spectacle lenses briefly, the two components of lens-compensation—changes in choroidal thickness and ocular elongation—are differentially affected, as though each component uses different visual information to guide it. To assess the generality of this finding we had chicks wear lenses under different levels of illumination. Methods: Chicks wore +8 or –8.6 D lenses over one eye for 3 days while maintained under 400, 2 or 0.2 lux diurnal illumination. Axial components were measured before and after 3 days of lens-wear, using A-scan biometry. Results: The change in depth of the vitreous chamber of the lens-wearing eye (relative to that in the fellow eye) was monotonically related to light intensity over the range of light intensities used. Thus at the lowest light intensity, negative lenses caused less than a quarter of the increase in vitreous chamber observed at the highest light level, and positive lenses caused a quarter as much inhibition of vitreous chamber elongation as at the highest light level. Light levels had different effects on different ocular components: The rate of ocular elongation was decreased by positive lenses and increased by negative lenses except at the lowest intensity. Choroidal compensation for positive lenses was impaired at even the middle illumination level, whereas choroidal compensation for negative lenses was not obviously light-dependent. Conclusions: Dim light progressively impairs lens-compensation, especially the choroidal response to positive lenses. This particular response was also the most sensitive to reductions in the frequency of brief periods of lens-wear (Winawer & Wallman, 2002). These results suggest that different signals control the choroidal thickness and ocular elongation components of lens-compensation and, presumably, of emmetropization.
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