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

The change in diameter of retinal vessels as a function of increasing dista nce to the optic disc is believed to be indicative of the risk level of var ious vascular diseases such as generalised arteriosclerosis and Diabetes Me llitus. In particular, focal arteriolar narrowing (FAN) is considered relat ed to;arteriosclerosis. The aim of this work is to develop methods to provi de quantitative information about the FAN status of retinal arteriolar vess el segments. We propose a method to measure the vessel diameter and changes herein along the vessel. The width or diameter measurement is based on int ensity profiles orthogonal to a smoothed trace in the vessel found by Dijks tra's shortest path algorithm. The vessel diameter is calculated from the i ntensity profiles using two different methods to estimate profile widths. W e propose a "normalised accumulated gradient" (NAG) and the coefficient 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 i ncreases. The performance of the methods developed is compared to the evalu ation by a skilled ophthalmologist. The methods are seen to perform well. ( C) 2000 Elsevier Science B.V. All rights reserved.