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Y. Li, K. Galichanin, R. Al-Saqry, P. Söderberg; Spectral Additivity for UVR-Induced Cataract. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2137.
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© ARVO (1962-2015); The Authors (2016-present)
To determine if spectral additivity of biologically efficient dose holds for in vivo ultraviolet radiation (UVR) induced cataract.
Six weeks old albino Sprague-Dawley rats were randomly divided into two groups of twenty rats each. The UVR source was a high pressure mercury arc lamp connected to a monochromator that was centered at maximum output at 300 nm (UVR-300 nm) and 310 nm (UVR 310 nm). Both groups of rats were exposed to 8 kJ/m2 biologically efficient dose as indicated by literature on spectral sensitivity. In each animal, one eye was exposed. One group received 300 nm only (8 kJ/m2 absolute dose during 70 min.) and the other group 300 nm (4 kJ/m2 absolute dose during 35 min) and 310 nm (42 kJ/m2 absolute dose during 35 min). One week after exposure, the rats were sacrificed, both lenses were extracted, the intensity of forward light-scattering was measured in transformed equivalent diazemuls concentration (tEDC). Then, macroscopic morphological lens changes were documented in dark-field illumination and in incident light with a grid background.
In vivo exposure to UVR-300 nm only, induced cortical cataract in all exposed lenses and occasionally nuclear cataract while the combination of UVR-300 nm and UVR-310 nm induced cortico-nuclear cataract in all exposed lenses. There was a significant difference of intensity of forward light scattering, (test statistic = 2.56, t(approx.)32;0.975 = 2.04) between lenses exposed to UVR- 300 nm only, CI(0.95) = 0.55 ±0.06 tEDC, d.f. = 19, and lenses exposed to the combination of UVR-300 nm and UVR 310 nm, CI(0.95)=. 0.64 ±0.04 tEDC, d.f = 19.
The combination of 300 nm and 310 nm causes more light scattering than 300 nm only at equivalent biologically efficient doses. Thus, strict spectral additivity of biologically efficient dose as obtained from experiments on narrow band exposures does not hold. However, the quantitative difference of induced light scattering is so little compared to the spectral variation in sensitivity at narrow band exposure that spectral additivity is a reasonable approximation for safety estimation.
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