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J.–M. Gorrand, M. Doly; Reflection from the RPE–Photoreceptor interface . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2791.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Different studies suggest that the directional component of light reflected by the retina comes from the RPE–Photoreceptor interface. The contribution of melanin granules to this process is controversial since melanin is highly absorptive but also has a very high refractive index. Our purpose was to determine whether light backscattered from melanine granules contributes significantly to the directional component radiated by photoreceptors towards the pupil. Methods: The modulation M and intensity I of interference fringes reflected by the fundus were mesured as a function of the angles of incidence and reflection in five eyes with a wide range of pigmentations. Interference fringes (wavelength : 514 nm) were projected onto the peripheral retina in Maxwellian view, and light reflected by the fundus was collected through a 1 mm diaphragm in the eye pupil. Results: The external image in the plane conjugate with the retina is the sum of two images due to the diffuse component (lowly modulated) and the directional component (hightly modulated), respectively. When the entrance and exit pupils are aligned to the photoreceptor axes, the modulation increases significantly with the intensity (p < 0.03). The equation of the regression line is M = 0.514 + 0.068 I, where I covers a range from 1 to 2.3 (arbitrary units) for the five subjects. Conclusions: Our results suggest that light backscattered from melanin granules does not contribute significantly to the directional component coming from the RPE–Photoreceptor interface. Despite their high refractive index, melanin granules absorb light without increasing the directional component. Moreover reflection by the discs inside outer segments seem small in comparison with reflection by the RPE–Photoreceptor interface.
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