Open-Angle Glaucoma

Open-angle glaucoma represents a group of optic neuropathies characterized by progressive loss of retinal ganglion cells and their axons, resulting in characteristic optic nerve head changes and corresponding visual field defects. The anterior chamber angle remains open on gonioscopy, distinguishing it from angle-closure glaucoma. Primary open-angle glaucoma (POAG) is the most common variant, though the category also includes normal-tension glaucoma (NTG), where damage occurs despite statistically normal IOP, and secondary forms such as pseudoexfoliative and pigmentary glaucoma.¹ Ocular hypertension (OHT) — elevated IOP without detectable optic nerve damage or visual field loss — represents a risk state rather than glaucoma itself. The condition typically progresses insidiously, and early detection combined with IOP-lowering treatment is essential to preserve vision.

The etiopathogenesis of primary open-angle glaucoma remains complex and incompletely understood. Proposed mechanisms include mechanical stress on the lamina cribrosa from elevated IOP, vascular insufficiency to the optic nerve head, and metabolic/oxidative injury, with individual variation in an eye's tolerance to a given IOP helping explain why some patients progress at statistically "normal" pressures.² Some proposed frameworks — a "dystrophic" (primary scleropathy) theory, an individual IOP tolerance norm concept, and a "liquor hypertension" concept involving cerebrospinal-fluid pressure gradients across the lamina cribrosa — are advanced primarily within a single review's synthesis rather than broad multi-group consensus, and are best treated as competing hypotheses rather than settled fact.² A systemic association with diabetes mellitus has also been described, though the direction of that relationship — shared vascular risk, a direct effect, or confounding by age and other systemic vascular disease — isn't yet resolved.³

Open-angle glaucoma typically presents insidiously without early symptoms: early disease is usually asymptomatic and detected only during routine eye examinations, while intermediate disease produces gradual peripheral visual field loss that patients often do not notice due to binocular compensation. Advanced disease can affect mobility and reading, and end-stage disease severely constricts the visual field or central vision. Because OAG is usually asymptomatic until advanced, diagnosis depends on screening exams rather than symptoms: routine IOP measurement, gonioscopy to confirm the angle is open, and assessment of the optic disc and visual field.¹

Key differentials: ocular hypertension (elevated IOP without optic nerve damage or field loss), physiologic optic disc cupping (large cups without progressive change), other optic neuropathies (ischemic, compressive, hereditary), neurologic visual field defects (stroke, intracranial mass), angle-closure glaucoma (narrow/closed angle on gonioscopy), and congenital glaucoma (enlarged globe, corneal edema in infancy).

Intraocular pressure is measured (traditionally elevated above 21 mmHg), though damage can occur at any pressure level; normal-tension glaucoma demonstrates progressive damage despite statistically normal IOP. Gonioscopy confirms an open anterior chamber angle, distinguishing OAG from angle-closure mechanisms, and may reveal pigment or pseudoexfoliative material in secondary forms. Optic nerve head assessment evaluates cup-to-disc ratio, inter-eye asymmetry, neuroretinal rim thinning or notching, disc hemorrhages, peripapillary atrophy, and nerve fiber layer defects. Visual field testing reveals characteristic patterns including nasal steps, arcuate scotomas, and paracentral defects, with generalized constriction in advanced disease. Optical coherence tomography quantifies retinal nerve fiber layer and ganglion cell layer thickness for early detection and progression monitoring, and central corneal thickness is measured since thinner corneas may lead to underestimation of true IOP.

The primary goal of treatment is to lower IOP to a level that slows or halts progression of optic nerve damage and visual field loss, following a stepwise approach. Topical IOP-lowering medications (prostaglandin analogs, beta-blockers, alpha-agonists, carbonic anhydrase inhibitors, cholinergic agents) have traditionally been first-line, used individually or in combination.

The Laser in Glaucoma and Ocular Hypertension (LiGHT) Trial randomized treatment-naive OAG/ocular hypertension patients to initial selective laser trabeculoplasty (SLT) versus topical drops. At 6 years, 69.8% of SLT-arm eyes remained at or below target IOP without needing medical or surgical treatment, and the SLT arm showed less disease progression (19.6% vs 26.8%) and fewer trabeculectomies and cataract surgeries than the drops arm.⁵ This is part of why current guidelines, including the Finnish Current Care Guideline, now support SLT as a reasonable first-line option alongside topical therapy.¹ LiGHT's population was treatment-naive with a defined retreatment protocol built into the trial infrastructure — real-world durability and retreatment logistics outside that structure are less well characterized, and its guideline recommendations shouldn't be generalized uncritically across healthcare systems.¹⁵ Direct selective laser trabeculoplasty (DSLT), a newer automated variant, is under investigation in the GLAUrious trial, which tests non-inferiority (not superiority) of a translimbal DSLT device against standard SLT in a treatment-naive population with untreated/washed-out IOP of 22-35 mmHg — a trial-specific enrollment criterion, not a general diagnostic threshold.⁴

When initial therapy is insufficient, escalation includes additional topical medications, repeat or alternate laser trabeculoplasty, or incisional glaucoma surgery (trabeculectomy, tube shunt). Target IOP is individualized based on severity of damage at presentation, rate of progression, and life expectancy, with regular monitoring of IOP, optic nerve appearance, and visual fields to detect progression.

• Open-angle glaucoma is typically asymptomatic until advanced, emphasizing routine screening in at-risk populations
• Normal IOP does not exclude glaucoma — normal-tension glaucoma accounts for a significant proportion of cases
• LiGHT trial data support considering SLT as first-line therapy alongside drops, though its findings describe a specific treatment-naive trial population⁵
• Optic disc hemorrhages are a sign of active glaucomatous damage and often herald progression
• Common pitfall: treating trial eligibility criteria (e.g., LiGHT/GLAUrious IOP ranges of 22-35 mmHg) as general diagnostic thresholds rather than study-specific enrollment parameters^5,4
• Common pitfall: assuming stable IOP means stable disease, without regular visual field and optic nerve monitoring
• Common pitfall: presenting single-source pathophysiologic frameworks (dystrophic theory, liquor hypertension concept) as established consensus²