COMPARISON OF METHODS OF MEASURING VESSEL WIDTHS ON RETINAL PHOTOGRAPHS AND EFFECT OF FLUORESCEIN INJECTION ON APPARENT RETINAL VESSEL CALIBERS

Four methods of measuring the widths of blood vessels in retinal photographs are compared: (1) measurement of a projected image with calipers; (2) direct visual measurement through a low-power microscope with a Nikken screw-micrometer eyepiece or (3) with an Olympus screw-micrometer eyepiece; and (4) indirect measurement with a simple microdensitometer. The method which employed an Olympus screw-micrometer eyepiece was found to be significantly (P < 0.01) more consistent than the other three methods; with it the 95% confidence interval for measurements expressed as dimensions on the retina was less than ± 3 micra. Vessels were measured slightly wider when their image was light on a dark background than when it was dark on a light background. All vessels had wider images (11% to 22%) in fluorescence angiograms than in standard retinal photographs. Intravenous fluorescein appeared to cause a generalized slight constriction of retinal vessels. © 1969.