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X.-R. Huang, R. W. Knighton; Wavelength Sensitive Change of Retinal Nerve Fiber Layer Reflectance in Glaucomatous Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5825.
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To assess glaucomatous damage, reflectance of retinal nerve fiber layer (RNFL) is often used, such as, in fundus photography and OCT. Because different scattering mechanisms appear to underlie the RNFL reflectance at different wavelengths, we postulated that change of RNFL reflectance in glaucoma depends on wavelength. This study measured reflectance spectra in glaucomatous retinas to reveal the wavelength dependent changes of RNFL reflectance.
Both normal and glaucomatous retinas were studied in Wistar rats. High intraocular pressure (IOP) was induced unilaterally by laser photocoagulation of trabecular meshwork. To measure reflectance of RNFL, an isolated retina was measured by means of imaging microreflectometry. The RNFL reflectance spectrum was calculated at different locations along bundles and normalized to the mean of the reflectance at 740 - 830 nm for comparison of spectral patterns. After reflectance measurements, the retina was stained with phalloidin to label F-actin and RNFL damage was assessed by confocal fluorescence imaging.
Reflectance spectra in normal retinas were identical along bundles, with reflectance high at visible wavelengths and deceasing at near infrared. In retinas with glaucomatous damage, reflectance at short wavelengths (400 - 460 nm) gradually decreased along bundles toward the optic nerve head (ONH) (Fig.). The short-wavelength loss was found in retinal regions with F-actin alteration as revealed by confocal imaging.
Elevation of IOP causes non-uniform change in the RNFL reflectance spectrum. Decrease of RNFL reflectance at short wavelengths implies that a short wavelength scattering mechanism is more sensitive to axonal damage than others. The result may provide a means to enhance early detection of glaucomatous damage.
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