Chronic open angle glaucoma is an etiologically heterogeneous group of diseases characterized by damage to the optic nerve, resulting in peripheral visual loss that can progress to involve the fovea and central vision. Open angle glaucoma can be divided into primary conditions and conditions which are secondary to another ocular or systemic disease. Causes of secondary glaucoma include uveitis, cataract, trauma, and disorders affecting the development structure of the angle. This review focuses on primary open angle glaucoma (POAG), since it accounts for the vast majority of the disease burden in the US population and its etiology remains unknown.