Purpose This study was conducted to investigate the prevalence and progression of glaucoma in patients receiving treatment for obstructive sleep apnea (OSA). We also investigated whether there is an association between severity of OSA and the incidence of glaucoma. Methods A total of 39 patients aged 430 years who had been diagnosed with moderate and severe OSA in the sleep clinic at Hamad General Hospital were assessed for the presence of glaucoma. The severity of OSA was graded as mild, moderate, or severe based on American Association of Sleep Medicine (AASM) criteria using the apnea hypopnea index. Before enrollment, all patients underwent a complete ophthalmic examination including serial visual field tests, optical coherence tomography (OCT) with fundus photographs, and pachymetry. Enrolled patients were followed up in the ophthalmology outpatient clinic and sleep clinic for a period of 3 years. Results Examinations found that 8 (20.5%; 95% confidence interval (CI) 9.9-37%) of the 39 patients with OSA had glaucoma. Six (75%; 95% CI 36-96%) of these patients had normal-tension glaucoma (NTG) and two (25%; 95% CI 4.5-64.4%) patients had hightension glaucoma. Among the 27 patients with severe OSA, 7 (25.9%; 95% CI 8-34%) had glaucoma, and among 12 patients with moderate OSA, 1 (8.3%; 95% CI 0.1-15%) had glaucoma. During the course of follow-up, two patients who previously did not have glaucoma were reclassified as NTG and two patients with glaucoma deteriorated. A higher prevalence of glaucoma in the severe OSA group compared with the moderate OSA group was found, albeit a statistically significant difference could not be attained (P ¼ 0.4). Conclusions Our study showed that severe OSA is an important risk factor for developing glaucoma. Adequate treatment of OSA, along with optimal ophthalmic care, resulted in better control of glaucoma.