ACCURATE VESSEL WIDTH MEASUREMENT FROM FUNDUS PHOTOGRAPHS - A NEW CONCEPT

Accurate determination of retinal vessel width measurement is importan t in the study of the haemodynamic changes that accompany various phys iological and pathological states. Currently the width at the half hei ght of the transmittance and densitometry profiles are used as a measu re of retinal vessel width. A consistent phenomenon of two 'kick point s' on the slopes of the transmittance and densitometry profiles near t he base, has been observed. In this study, mathematical models have be en formulated to describe the characteristic curves of the transmittan ce and the densitometry profiles. They demonstrate the kick points bei ng coincident with the edges of the blood column. The horizontal dista nce across the kick points would therefore indicate the actual blood c olumn width. To evaluate this hypothesis, blood was infused through tw o lengths of plastic tubing of known diameters, and photographed. In c omparison with the known diameters, the half height underestimated the blood column width by 7.33% and 6.46%, while the kick point method sl ightly overestimated it by 1.40% and 0.34%. These techniques were appl ied to monochromatic fundus photographs. In comparison with the kick p oint method, the half height underestimated the blood column width in veins by 16.67% and in arteries by 15.86%. The characteristics of the kick points and their practicality have been discussed. The kick point method may provide the most accurate measurement of vessel width poss ible from these profiles.