Quantitative Measurement of Changes in Retinal Vessel Diameter in Ocular Fundus Images

The Change in diameter of retinal vessels as a funcion 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 measurements is based on intensity profiles orthogonal to a smoothed trace in the vessel found by Dijkstra´s shortes path algorithm. The vessel diameter is calculated from the intensity profiles using two different methods to estimate profile widths. We propose a "Normalised Accumulated Gradient" (NAG) and the Coefficient of Variance (CV) to estimate the Focal Arteriolar Narrowing (FAN) in a vessel segment. The normalised Accumulated Gradient (NAG) is designed to detect inceases 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.