Analysis of vessel absorption profiles in retinal oximetry

The optical densities of vessel absorption features in small bandwidth fundus photographs have been used by many people for finding the oxygenation of the blood in retinal vessels. The purpose of this article is to show that the information found in this way can be made more accurate, and more information can be found by considering the details of the absorption profile (intensity as a function of distance across the vessel). The "wings" of the profile are primarily determined by the line-spread function of the video camera or film. A four-parameter curve fitting procedure using the line-spread function and an "ideal" vessel profile can be used to eliminate the effects both of the line-spread function and of any central reflection (vessel reflex) that may be present, yielding estimates of the vessel diameter and central absorption. The conclusions concerning the reflection are supported by studies of reflections from capillary tubes and wires in a model eye.