Sleep apnea is characterized by repetitive episodes of decreased or interrupted airflow in the upper airways during sleep. Obstructive sleep apnea syndrome (OSAS) is the most common sleep-related breathing disorder and is characterized by repeated partial or complete upper airway collapse, gasping episodes, daytime sleepiness and fatigue. Once suspected, the diagnosis is made on the basis of anamnesis and a polysomnography (PSG) using the so-called respiratory disturbance index (RDI) to grade OSAS. Standard therapy consists of continuous positive airway pressure (CPAP) during sleep to prevent upper airway collapse. The association between OSAS and glaucoma has been extensively studied, although a few reports have been non-confirmatory. OSAS has been associated with reduced ocular blood flow, leading to hypoxia and hypercapnia, and as such, may represent a risk factor for glaucomatous optic neuropathy. OSAS has also been related to loss of nycthemeral rhythm of intraocular pressure (IOP). In addition, CPAP has been reported to increase IOP when used during nighttime.