Quantitative measurement of changes in retinal vessel diameter in ocular fundus images

The change in diameter of retinal vessels as a function of increasing distance to the optic disc is believed to be indicative of the risk level of various vascular diseases such as generalised arteriosclerosis and Diabetes Mellitus. In particular, focal arteriolar narrowing (FAN) is considered related to arteriosclerosis. The aim of this work is to develop methods to provide quantitative information about the FAN status of retinal arteriolar vessel segments. We propose a method to measure the vessel diameter and changes herein along the vessel. The width or diameter measurement is based on intensity pro®les orthogonal to a smoothed trace in the vessel found by Dijkstra's shortest path algorithm. The vessel diameter is calculated from the intensity pro®les using two di€erent methods to estimate pro®le widths. We propose a ``normalised accumulated gradient'' (NAG) and the coecient of variance (CV) to estimate the FAN in a vessel segment. The NAG is designed to detect increases in the vessel diameter as the distance to the papilla increases. The performance of the methods developed is compared to the evaluation by a skilled ophthalmologist. The methods are seen to perform well. Ó 2000 Elsevier Science B.V. All rights reserved.