REFLECTANCE PULSE OXIMETRY MEASUREMENTS FROM THE RETINAL FUNDUS

Conventional transmission pulse oximetry is a noninvasive technique fo r the continuous monitoring of arterial oxygen saturation (SaO(2)) fro m peripheral vascular beds;such as the finger tip or earlobe. In this paper we propose to exploit the unique transparency of the ocular medi a to make reflectance pulse oximetry measurements on the retinal fundu s. This technique potentially offers significant advantages over conve ntional pulse oximetry, primarily the ability to monitor cerebral, as opposed to peripheral, oxygen saturation. We have developed an in vitr o system to simulate the retinal circulation and ocular optics. This s ystem consists of a flexible cuvette located in a model eye and an ext racorporeal blood circuit to simulate arterial blood flow. The system was used to investigate the relationship between SaO(2) and the R/IR r atio in reflectance pulse oximetry. To enable in vivo measurements to be made, we also modified a standard haptic contact lens to hold the p ulse oximeter probe in front of the pupil. In a preliminary study, the lens was fitted to an awake volunteer and cardiac-synchronous signals were detected by the retinal pulse oximeter.