An automatic system for the estimation of generalized arteriolar narrowing in retinal images

Generalized arteriolar narrowing, an eye fundus sign often seen in patients affected by hypertensive or diabetic retinopathies, is usually expressed by the arteriolar-to-venular diameter ratio (AVR), a numerical parameter derived from caliber measurements on specific vessels. We developed a system to compute AVR in a totally automatic way. Images are at first enhanced to highlight the vessel network, which is then traced by a vessel tracking algorithm. From the detected vessel structure, the position of the optic disc is derived and the region inside which the AVR data are to be measured is determined. Vessels within this region are labeled as either arteries or veins and their caliber is estimated from tracing data. From these values, the AVR parameter is computed. Results provided by this system have been compared with manually derived AVR values on 14 eye fundus images from normal and hypertensive subjects.