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G. Staurenghi, C. Luiselli, G. Levi, F. Viola, F. Delori; Retinal photopigment density measured using autofluorescence imaging . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2795.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To test the feasibility of using autofluorescence imaging to measure the photoreceptor’s pigment distribution in normal subjects. Methods: Fourteen normal subjects were studied using autofluorescence imaging obtained using a confocal scanning laser ophthalmoscope (Heidelberg Retinal Angiograph, Heidelberg Engineering GmbH, Dossenheim, Germany). The excitation wavelength was 488 nm (Emi. > 520 nm), the field was 30x30°, and images were acquired at 6/images per second (retinal irradiance: 230 microW/cm2). Autofluorescence images for the dark adapted state, were obtained after 20 minutes of dark adaptation and for the light adapted state after 4 minutes of bleaching with 514 nm (110 microWatts/cm2). Four images were averaged in each adaptation state, and grey levels were measured over 2x2° test field at the fovea, and at 4°, 8° and 12° eccentricity. The retinal photopigment density (at 488 nm) was equal to the difference of the logarithms of the light and dark adapted autofluorescence images. Results: The mean density at 488 nm increases from the fovea (0.085 +/– 0.035 D.U.) to the periphery: the mean densities were 0.097+/– 0.007 D.U., 0.103 +/– 0.023 D.U., and 0.117 +/– 0.027 D.U. at 4, 8, and 12°, respectively. The range of densities at 12° was 0.01 to 0.20. Paired statistical comparison showed significant difference between the fovea and the eccentric sites at 4° (p< 0.008), 8° (p< 0.002), and 12° (p<0.003). Conclusions: The spatial changes observed suggest that rods densities are principally measured in all experimental procedure. The densities are in a similar range than data in the literature obtained with different instruments. The reliability of the measurement is critically affected by alignment and changes in pupil diameter. This study suggests that measurement of photopigment is possible using autofluorescence imaging by means of a confocal scanning laser ophthalmoscope. Refinements could include bleaching part of the field and performing direct comparison between the bleached and dark adapted areas.
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