Reflectometric Measurement of Retinal Oxygen Saturation in Patients With COPD Grade IV and Healthy Subjects

An adequate oxygenation and retinal perfusion is essential for the function of the inner retina. There is a wide range of autoregulation mechanisms to ensure a sufficient ocular blood and oxygen supply during changes in systemic blood pressure or intraocular pressure (IOP). Nonetheless, various retinopathies such as diabetic retinopathy, which is the leading cause of blindness in people aged 20-65 in the western world, are highly associated with hypoxia (Pemp and Schmetterer 2008). Hence, measurements of oxygen levels in retinal vessels are needed to further our understanding of these ischemic diseases. It is a well known fact and a commonly employed method to measure oxygen saturation of blood through light transmission (Kramer 1934). However, this approach is not feasible in the human eye. Therefore, reflection must be used, meaning the amount of incident light must be estimated based on the amount of light reflected (for a review see Harris 2003). This is a difficult task and investigators in this field have encountered several problems, including optical complexities, nonlinear sensors and eye movement (Beach et al 1999; Delori 1988). Nonetheless considerable progress has been made over the past decades and the development of an reliable oximeter reported (Hardarson et al 2006).

In the present study this technique will be applied in healthy subjects as well as in patients with COPD during room-air conditions. The procedure takes approximately 15 minutes in each subject and will be performed in only one eye.