Healthy subjects:

Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study

Treatment in the previous 3 weeks with any drug except oral contraceptives

Symptoms of a clinically relevant illness in the 3 weeks before the study day

Blood donation during the previous 3 weeks

COPD patients:

Abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study

Health status which does interfere with study procedure or their safety

Blood donation during the previous 3 weeks

Symptoms of a clinically relevant illness other than COPD or COPD related in the 3 weeks before the study day

Reflectometric Measurement of Retinal Oxygen Saturation in Patients With Chronic Obstructive Pulmonary Disease (COPD) Grade IV and Healthy Subjects