Validation of retinal oxygen measurement using OCT

Optical coherence tomography (OCT) is a widely used technique in biomedical imaging. Due to the unprecedented depth resoltuion of the technique application in a variety of medical fields has gained much interest. A system for the imaging of the human fundus based on OCT is on the market, which provides a depth resoltuion in the order of 10-15 micrometers. Recently, an ultrahigh resolution OCT technique has been developped by using a titanium sapphire laser as a light source. This instrument has successfully been used to image the human retina with a depth resolution of 2-3 micrometers. In this project this technique will be extended to allow for retinal oxygen measurement. This is based on a spectroscopic approach employing the large bandwidth of the laser (approximately 200 nanometers). Considering the different absorption characteristics of oxyhemoglobin and desoxyhemoglobin we propose a method for measuring retinal oxygen saturation. This is achieved by frequency analysis of the light reflected and back scattered by retinal structures behind larger retinal vessels. By concomitant blood flow measurement this allows for determination of the retinal oxygen availability/demand ratio which provides a measure for tissue hypoxia. This technique will first be applied in an in vitro model, which allows for measurements in tubes filled with blood with defined oxygen saturation. Thereafter we propose to investigate the suitability of this technique in vivo by studying the rat retina at different levels of systemic hyperoxia and hypoxia. This is achieved by breathing gas mixtures with different fractions of oxygen. Measurements will be validated by comparison with the invasive microelectrode technique as a gold standard. To gain insight into the applicability of such a system in ocular disease, measurements in rats with experimentally induced retinal branch vein occlusion are scheduled.