Background: obstructive sleep apnea seems to have multi-organ harmful effects. Its association with glaucoma was previously reported. However, the debate exists around prevalence of glaucoma and the pathophysiology explains its association with obstructive sleep apnea is not fully known. Objective: the present study was designed to estimate the incidence of normal tension glaucoma among patients with obstructive sleep apnea. Patients and Methods: sixty patients with obstructive sleep apnea and another age and sex matched 60controls were included. Five patients in the study group refused to complete the study and only 55 patients constitute the study group.Allparticipants underwent polysomnographic and ophthalmologic (measurement of intraocular pressure and fundus examination) studies. Data was collected, documented and statistically analyzed. Results: both study and control groups were comparable regarding patients' demographic and associated chronic medical disease. The prevalence of normal tension glaucoma in patients with obstructive sleep apnea was 27.3% and it was 3.3% in control subjects. Cup disk ratio and oxygen desaturation index were significantly increased, while oxygen saturation significantly decreased in patients with obstructive sleep apnea. In addition, obstructive sleep apnea index (measure of severity) was proportionately correlated with intraocular pressure, oxygen desaturation index, cup to disk ratio and negatively correlated with oxygen saturation. Conclusion: open angle glaucoma significantly increased in obstructive sleep apnea and significantly associated with disease severity.