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K. R. Denninghoff, D. A. Salyer, S. Basavanthappa, K. Twietmeyer, R. I. Park, R. A. Chipman; Diffuse Spectral Fundus Reflectance Measured Using Subretinally-Placed Spectralon. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3843.
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© ARVO (1962-2015); The Authors (2016-present)
To measure the diffuse fundus reflectance and the spectral transmittance of the swine sensory retina in vivo using intravitreal illumination.
Pars plana vitrectomy and intravitreal manipulations were performed on a female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiber optic intraocular illuminator inserted into the vitreous. Intravitreal illumination is employed to reduce the effects of extraneous reflections and scatter from the anterior structures of the eye. The fundus was illuminated at an oblique angle and a 2 mm2 ( this is 1.4 mm x 1.4 mm ?) region imaged. Multispectral retinal images were acquired for four experimental conditions: the eye prior to vitrectomy, after vitrectomy, after insertion of a small Spectralon disk super-retinally, and after insertion of the Spectralon disk beneath the inner retina. The diffusely reflected flux was integrated over the pupil with a solid angle of 0.028 steradians. The illuminated area moves due to swine motion, primarily breathing. To minimize this movement of the light source relative to the retina, the light pipe was fixed to the globe. The animal was anesthetized during the procedure.
Three areas of fundus were analyzed from the same field of view for each measurement condition and relative fundus reflectance was calculated. The absorption of melanin and hemoglobin in the red wavelengths was used to convert relative spectral reflectance measurements to absolute reflectance measurements. The flux scattered from the super retinal Spectralon was used to correct for scattering in the globe. The transmittance of the sensory retina was measured in vivo using the scatter corrected subretinal Spectralon disk reflectance.
By measuring with both super and subretinal Spectralon, the hemoglobin and melanin components of the spectrum due to scattered light can be removed from the retinal transmission spectrum. The in vivo spectral transmittance of the sensory retina in this animal was essentially flat across the visible spectrum, with an average transmittance > 90%. Fundus reflectance measured using intravitreal illumination showed relative spectral behavior typical of past human fundus measurements. Modeling the absorption of melanin and hemoglobin matched the in vivo retinal reflectance behavior in the yellow to red regions of the spectrum, but the blue green region of the visible spectrum was brighter than predicted by the same model.
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