Glaucoma is a leading cause of irreversible blindness worldwide. Normal tension glaucoma (NTG) is a challenging subtype in which progressive changes to the optic nerve and retinal ganglion cell (RGC) function occur despite normal intraocular pressures (IOP). In most types of glaucoma, elevated IOP is the major risk factor and a key target for medical therapy. The absence of IOP elevation in NTG poses diagnostic dilemmas and therapeutic challenges. The disease is often diagnosed late, with irreversible atrophic changes to the optic nerve and permanent loss of vision. These clinically manifested structural and functional changes seen on optical coherence tomography (OCT) and visual field (VF) tests are likely preceded by a subclinical stage at which RGCs become increasingly dysfunctional before dying.

Obstructive sleep apnea (OSA) is characterized by intermittent nocturnal upper airway collapse, leading to oxygen deprivation and hypoxemia. It is a common cause of daytime sleepiness and is associated with an increased likelihood of hypertension, cardiovascular disease, stroke, and diminished quality of life. Continuous Positive Airway Pressure (CPAP) therapy is an established treatment for moderate to severe OSA in which patients sleep with a special mask that helps to regulate inspiratory and expiratory flow, alleviating hypoxia.

The investigators hypothesize that eliminating the hypoxia induced by OSA could have a favorable effect on retinal blood flow, thereby reducing the likelihood of progressive RGC damage and dysfunction in subjects at risk for NTG. The investigators are proposing a prospective, longitudinal, non-randomized study to evaluate the role of innovative diagnostic technologies in the early detection of NTG, and to establish its association with OSA. Additionally, the investigators will monitor the effects of OSA treatment in preventing the development of the disease, or at least halting its progression. Special attention will be given to the sex differences in the analysis to recognize the substantial differences in OSA between men and women, as well as the prevalence of NTG in different OSA severity groups.

While under the care of a Sleep Medicine physician, newly diagnosed subjects with OSA interested in participating will be recruited from the Northwell sleep center. Prior to initiating continuous positive airway pressure therapy (CPAP), consented participants will be screened to satisfying the eligibility criteria, and undergo a complete ophthalmological exam. Functional and structural diagnostic testing will be performed to evaluate baseline measures, including visual field testing, OCT, pattern electroretinography (PERG) and optical coherence tomography-angiography (OCTA) testing. Using the American Association of sleep Medicine (AASM) criteria, 3 groups will be formed based on the apnea-hypopnea index (AHI). The severity of OSA is graded as mild (AHI\<15), moderate (15\<AHI\<30), or severe (AHI\>30). The Epworth questionnaire will be used as part of routine clinical care to monitor improvement or deterioration after treatment. Once the baseline ophthalmological exam has been performed, subjects will return to the sleep center to begin CPAP therapy for OSA. Three follow up ophthalmic exams will be performed at 3, 6, and 9 months after initiating CPA therapy.