Primary Open-Angle Glaucoma
Primary open-angle glaucoma (POAG) is typically a chronic, slowly progressive optic neuropathy with characteristic patterns of optic nerve damage and visual field loss. Numerous clinical factors affect an individual’s susceptibility to POAG, which is a multifactorial disease process. These factors include intraocular pressure (IOP), age, race, central corneal thickness, myopia, and a family history of glaucoma. Other factors that may contribute to disease susceptibility include low corneal hysteresis, low ocular perfusion pressure, low cerebrospinal fluid pressure, abnormalities of axonal or ganglion cell metabolism, and disorders of the extracellular matrix of the lamina cribrosa. Unfortunately, we do not yet fully understand the interplay of the multiple factors involved in the development of POAG. Secondary open-angle glaucoma (OAG) differs from POAG in that identifiable factors contribute to its development, such as the dispersed pigment in pigmentary glaucoma and the pseudoexfoliative material of pseudoexfoliation syndrome. (For more on secondary OAG, see Chapter 8.)
POAG is typically insidious in onset, slowly progressive, and painless. It is usually bilateral but can be asymmetric. Patients may seem relatively asymptomatic until the later stages of the disease, when central vision is affected. POAG is diagnosed with findings from the assessment of the optic nerve and nerve fiber layer and the results of visual field testing.
The diagnosis of POAG requires verification that the anterior chamber angle is open. Gonioscopy (discussed in Chapter 4) is indicated for all patients evaluated for glaucoma. In patients with established OAG, gonioscopy should be repeated periodically to monitor for progressive angle closure caused by lens-induced changes, particularly in patients with hyperopia. Repeated gonioscopy is also indicated when the anterior chamber becomes shallow, when strong miotics are prescribed, after argon laser trabeculoplasty* (ALT) or laser peripheral iridotomy has been performed, and when IOP increases.
Optic nerve head appearance and visual fields
Although elevated IOP is an important risk factor for OAG, diagnosis of this disease is based primarily on the appearance of the optic nerve head, or optic disc, and on the results of visual field testing. See Chapters 5 and 6 for a detailed discussion of the optic nerve and visual fields. Careful periodic evaluation of the optic nerve and visual field testing are essential in the management of glaucoma. Stereophotographic documentation of the optic nerve or computerized imaging of the optic nerve, retinal nerve fiber layer, and macula aids the detection of subtle changes over time. Visual field loss typically correlates with the appearance of the optic nerve, and significant discrepancies between the pattern of visual field loss and optic nerve appearance warrant additional investigation.
American Academy of Ophthalmology Glaucoma Panel, Hoskins Center for Quality Eye Care. Preferred Practice Pattern® Guidelines. Primary Open-Angle Glaucoma—2015. American Academy of Ophthalmology; 2015. www.aao.org/ppp
Jonas JB, Budde WM, Panda-Jonas S. Ophthalmoscopic evaluation of the optic nerve head. Surv Ophthalmol. 1999;43(4):293–320.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.