Optical imaging of retinal blood flow: Studies in automatic vessel extraction, alignment, and driven changes in vessel oximetry

Abstract

Recent advances in retinal imaging have made it possible to take measurements of retinal oxygen saturation noninvasively in humans. This allows studying the supply of oxygen in healthy and diseased retinae, thereby advancing our understanding of both the normal functioning of the retina and of retinal pathologies. However, retinal oximetry is still a research tool only and requires further improvement before being used in a clinical setting.Here, a single-wavelength flickering light was used to increase retinal blood flow in healthy subjects. This increase is revealed by both vasodilation and an increase in retinal oxygen saturation. A flickering light stimulus provides the means to assess the sensitivity of any retinal oximetry system, as such systems should be able to pick up this increase in retinal blood flow. In addition, the flickering light allows for com- parison to be made within rather than between subjects and can be used to examine the activation of the eye. This reduces the influence of potential confounding factors between subjects including differences in fundus pigmentation and illumination. The most commonly used method to measure retinal oxygenation is the optical density ra- tio (ODR) approach. The standard approach is to compute the average ODR for each vessel segment by combining the hundreds of individual ODR readings and then to use the mean of these segment averages as a measure of oxygen saturation. Alternatively, it has been suggested that the peak location of Gaussian functions fitted to histograms of individual ODR readings can be used as an measure of retinal oxygenation.In response to a 10Hz flickering light, the venular diameter increased by 3.44% (SEM: ±0.53%) (n=16, p

Date of Award	1 Aug 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Niall Mcloughlin (Supervisor) & Ingo Schiessl (Supervisor)