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N.P. Zagers, D. van Norren; Photoreceptors Act as Spectrally Flat Reflectors . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2873.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have build an instrument for simultaneous measurement of the spectral and directional reflectance of the fovea (Appl.Opt. 2002,41:4686). In our spectral fundus reflectance model, the directional reflectance is considered to originate from the cone photoreceptor cells (Vis.Res. 1996,36:2229). This reflectance is assumed to be spectrally flat. We investigated the relation between the amplitude of the directional reflectance and the wavelength in a number of pseudophakic subjects, with the purpose to put a test on this aspect of our model. Methods: The study included 5 eyes of 5 subjects with an IOL. Light reflected from a 2 deg spot concentric with the fovea was analyzed with an imaging spectrograph. The entrance slit of the spectrograph, conjugate to the pupil plane, defines a bar shaped exit pupil (1 x 12 mm). The spectrograph image contained profiles exhibiting directional reflectance versus wavelength. Each 5 nm bandwith profile in the range 420 to 600 nm was fitted with a Gaussion function, on top of a constant background. The amplitude of the Gaussian, our measure for the photoreceptor reflectance, was converted to a density using D = -Log(A/100). This density versus wavelength was fitted with two terms: A constant, accounting for the reflectivity of the photoreceptors, and the density of macular pigment. Absorption in the cornea and the vitreous was neglected, and a minor fixed correction for spectral absorption in the IOL was applied. Results: It proved possible to describe the data with the two component model. Mean reflectance from the photoreceptors was 0.4 ± 0.2%, mean macular pigment density at 460 nm was 0.53 ± 0.09. Conclusions: The results confirm some of the assumptions underlying our spectral fundus reflectance model. The data demonstrate that reflectance from the photoreceptors shows little, if any, wavelength dependence.
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