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J.E. Coppens, L. Franssen, T.J. T. P. van den Berg; Spectral Dependence of Retinal Straylight . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4325.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Wavelenght dependence of retinal straylight has remained somewhat of an enigma since Stiles in 1929 supposed it to have the same strong Rayleigh type –4 wavelenght dependence as small particle light scattering (the blue of the sky). However, experiments failed to show dependence for retinal straylight (lastly Whitaker, Steen and Elliott OVS93; review Wooten and Geri VR87), leading these authors to conclude that light scattering in the eye does not originate from small particles. Yet there is strong experimental evidence for such dependence of scattering by the eye lens (van den Berg IOVS96&97) and cornea (van den Berg and Tan, VR94). Earlier the failure to find this type of dependence was suggested to be due to the presence of an opposed dependent source of light scattering in the pigmented structures of the eye, in combination with a lack of precise measurement techniques (van den Berg et al. VR91). Methods: With the "compensation comparison" method (this ARVO) a much improved measurement technique was developed and used to reinvestigate the dependence of retinal straylight from 457 to 625 nm. Subjects were included with a wide range of pigmentations: 11 blue–eyed, 9 green–eyed, 7 brown–eyed caucasians, and 5 dark–brown–eyed negroids. Ages were from 21 to 81 years. Results: Spectral dependence of retinal straylight was found to strongly depend on the state of pigmentation of the eye in addition to age. Young and well pigmented eyes (young negroids) show a nearly –4 dependence. With higher age and/or less pigmentation straylight increases for all wavelengths, but most strongly at the long wavelength side, until it is almost equal at 625 and 457 nm, with a weak minimum in between. The dependence of retinal straylight could be modeled as the sum of 3 components: (1) a constant nearly –4 dependent component + (2) a pigmentation dependent component rising sharply at the long wavelength side + (3) an age dependent spectrally relatively flat component. This model resembles an earlier model for angular dependency (van den Berg OVS95). The same weighting functions could be applied. Conclusions: The psychophysical retinal straylight phenomenon shows dependence that corresponds with data about the individual light scattering processes in the eye. The –4 type of light scattering in the cornea and young lens shows up clearly in the young well pigmented eye. With less pigmentation a strong red dominated component originating from reflectance of the fundus and transmittance through the eye wall (van den Berg et al. VR91) adds to it, negating this dependence. Moreover with aging, a more or less spectrally neutral component is added from the eye lens.
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