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A.E. Mosher, M.D. Knudtson, K.N. Jensen, R. Klein, B.E. K. Klein, L.D. Hubbard, N.J. Ferrier; Comparison of Retinal Vessel Measurements in Digital vs. Film Images . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3281.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare retinal vessel caliber measurements from digital and film images. Methods: Twenty–five people were recruited to have color digital retinal images of the disc (DRS Field 1) captured in both eyes through pharmacologically dilated pupils using a 45° camera (6.3 mega pixels). At the same sitting, 30° color film images were also taken of the same eyes (n = 25). The slide transparencies (film) were digitized by scanning, and a conversion factor (microns/pixel) was determined to adjust for the difference in scale between image types. Vessel measurements were taken from the digitized film image and the natively digital–captured image using a semi–automated computer program. All images were graded according to an established protocol, and no regard was given to measuring at exactly the same vessel locations in the corresponding images. The central retinal artery equivalents (CRAE) and central retinal vein equivalents (CRVE) were calculated by combining diameters of the six largest of each vessel type. Comparisons were made for the vessel equivalents and for the arteriole–to–venule ratio (AVR) as ascertained from both types of images. Results: The mean (SD) result from natively digital images vs. digitized film images was 147.6 Φm (18.6) vs. 145.0 Φm (15.4) for CRAE, 215.5 Φm (21.0) vs. 216.4 Φm (22.0) for CRVE, and 0.69 (0.06) vs. 0.67 (0.07) for AVR. Pearson correlations between the three vessel measurements from digital vs. film images were CRAE = 0.89, CRVE = 0.90, and AVR = 0.82. Conclusions: Retinal vessel caliber measurement on digital images is highly comparable to that on film–based images. Beyond differences in image mode, some variation may also result from different image quality, different grader decisions, and variation of the point in the cardiac cycle when the photographs were captured.
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