Primary Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is a chronic, progressive optic neuropathy that silently destroys retinal ganglion cells and their axons, producing characteristic optic nerve and visual field changes. It is the most common form of glaucoma and a leading cause of irreversible blindness globally. The absence of symptoms in early and moderate disease makes detection through comprehensive eye examination essential.

POAG affects an estimated 60–70 million people worldwide. Prevalence increases significantly with age and is substantially higher in individuals of African descent. Family history confers a 3–10 fold increased risk. It is the most common cause of irreversible blindness in African Americans.

The fundamental pathology is progressive loss of retinal ganglion cells (RGCs) and their axons, resulting in characteristic structural changes to the optic nerve head (ONH) and retinal nerve fiber layer (RNFL). The mechanism of RGC death involves a combination of mechanical compression at the lamina cribrosa, vascular insufficiency, and neurotoxic processes.

Elevated intraocular pressure (IOP) is the primary modifiable risk factor, acting through mechanical deformation of the lamina cribrosa and compression of axonal transport. However, POAG can progress at statistically normal IOP levels (normal-tension glaucoma), indicating that IOP-independent mechanisms — including vascular dysregulation, oxidative stress, and neuroinflammation — contribute to disease.

Aqueous humor dynamics are central to IOP regulation. Resistance to outflow through the trabecular meshwork is the primary mechanism of IOP elevation in POAG.

POAG is typically asymptomatic until significant optic nerve damage has occurred. Peripheral visual field loss develops insidiously, and patients rarely notice deficits until the mid-peripheral or central field is affected. Clinical signs include increased cup-to-disc ratio, focal or diffuse RNFL thinning, optic disc hemorrhages, and characteristic visual field defects (arcuate scotomas, nasal steps, paracentral defects). IOP may be elevated, normal, or fluctuating.

IOP reduction is the only proven treatment for POAG. The target IOP is individualized based on baseline IOP, degree of optic nerve damage, rate of progression, and patient life expectancy. A 20–30% reduction from baseline is a common initial target.

Prostaglandin analogues (latanoprost, bimatoprost, travoprost, tafluprost) are first-line therapy due to their efficacy, once-daily dosing, and favorable systemic safety profile. Beta-blockers, alpha-agonists, and carbonic anhydrase inhibitors are used as adjunctive or alternative agents. Rho kinase inhibitors (netarsudil) and fixed-dose combinations expand the therapeutic armamentarium.

Laser trabeculoplasty (SLT) is an effective first-line or adjunctive option with a favorable safety profile. Surgical intervention (trabeculectomy, tube shunt, MIGS procedures) is reserved for inadequate IOP control on maximal tolerated medical therapy.

Monitoring frequency is determined by disease severity and stability. Newly diagnosed or recently treated patients require more frequent visits (every 1–3 months). Stable patients on established therapy may be monitored every 6–12 months. Each visit should include IOP measurement, optic nerve assessment, and periodic visual field and OCT testing. Progression analysis requires serial data — a minimum of 5–6 visual fields over 2 years for reliable trend analysis.