 All these experiments will be performed in the 4 groups glaucoma patients,OSA patients, patients with OSANAION, healthy subjects. A resting period of at least 20 minutes in a sitting position is scheduled for each subject before the study and 30 minutes between experiment. Stable baseline conditions are established, which are ensured by repeated measurements of blood pressure. Other conditions such as abstinence from coffee, alcohol drinking, smoking, refrain from heavy meal, exercise, etc, all of which may affect the measurement of blood flow are prohibited. Adequate dilatation of the patients pupil is necessary using a muscarinic antagonist i.e. tropicamide. 