A New Method of Measuring Retinal Vessel Diameters from Fundus Photographs Based on Retinal Structure and Light Reflection

We propose a new method and software for measuring blood vessel diameters from fundus photographs. In this method the edge of the blood vessel is the two minimum points in the luminance profile and diameter is distance between minimum points. We noticed the relation between W-shape of luminance profile at blood vessel transversal line and cylindrical shape, and analyzed the validity of this method using the diffuse reflection model of a cylinder shape based on the optics. The simulation image by the diffuse reflection model of the cylinder was similar to that of the blood vessel images. A newly developed software using the minimum points can measure repeated measurement in a series of photographs at the same point of the same person. The data of the repeated measurement of each person showed stability, and the coefficient of variation showed no affection of different diameter and arteriovenous distinction. Hence, we believe that the minimum points are valid as blood vessel edges. The software that measures these blood vessel edges has an extremely simple measurement procedure, possesses few errors, and is easy to automate. This method is relevant because the central reflex, which has not been utilized previously, optically represents the cylindrical three-dimensional structure of blood vessels.