Why is open-angle glaucoma often called a 'silent' disease?

Vision loss typically begins in the peripheral field and progresses slowly while central vision is preserved until late, so many people are unaware of damage until a substantial part of the visual field has already been lost.

Can someone have open-angle glaucoma with normal eye pressure?

Yes. In normal-tension glaucoma the characteristic optic nerve and visual field damage occurs even though intraocular pressure stays within the statistically normal range, which is why glaucoma is defined by optic nerve damage rather than pressure alone.

Open-Angle Glaucoma

Open-angle glaucoma is the most common form of glaucoma, a chronic progressive optic neuropathy in which the anterior chamber drainage angle remains anatomically open yet aqueous outflow resistance rises, contributing to elevated intraocular pressure and gradual, typically painless loss of the visual field. Its insidious course means damage often accumulates before symptoms are noticed.

Definition

Open-angle glaucoma is a chronic optic neuropathy with characteristic optic disc and visual field damage occurring while the anterior chamber angle is gonioscopically open, in which increased trabecular outflow resistance is the typical driver of elevated intraocular pressure.

Scope

The topic covers the defining mechanism of open-angle glaucoma, its principal risk factors, the rationale for intraocular pressure as the modifiable target, and the landmark trials that established the link between pressure lowering and slower progression. It treats open-angle glaucoma as a clinical-entity reference topic and offers no individualised diagnostic or treatment guidance.

Core questions

Why does intraocular pressure rise when the drainage angle is anatomically open?
What distinguishes high-tension from normal-tension open-angle glaucoma?
How strong is the evidence that lowering intraocular pressure slows progression?
Which factors beyond pressure influence risk and rate of optic nerve damage?

Key concepts

Trabecular outflow resistance
Primary open-angle glaucoma
Normal-tension glaucoma
Ocular hypertension
Optic disc cupping
Retinal nerve fibre layer thinning
Pressure-lowering as a modifiable target

Mechanisms

In open-angle glaucoma the trabecular meshwork remains anatomically accessible, but outflow resistance increases, so aqueous humour drains less efficiently and intraocular pressure tends to rise. Sustained mechanical and vascular stress at the optic nerve head leads to progressive apoptosis of retinal ganglion cells and loss of their axons, producing enlarging optic disc cupping and corresponding arcuate visual field defects. Because pressure is only one contributor, some eyes sustain damage at statistically normal pressures (normal-tension glaucoma) while others tolerate elevated pressure without damage (ocular hypertension), underscoring that pressure is a risk factor rather than the disease itself (Weinreb 2014; Jonas 2017).

Clinical relevance

Open-angle glaucoma is a major cause of irreversible vision loss and, because it is usually asymptomatic until advanced, illustrates why understanding risk factors and detection methods matters in ophthalmology and public health. The randomised evidence that lowering intraocular pressure slows progression is foundational to how the disease is studied. This entry describes that evidence base and is not a substitute for individual clinical assessment.

Epidemiology

Open-angle glaucoma accounts for the majority of glaucoma worldwide; the same meta-analysis that estimated roughly 64 million people with glaucoma in 2013 found open-angle disease to be the predominant subtype overall, with higher burden in populations of African ancestry and rising prevalence with age (Tham 2014).

Evidence & guidelines

Three landmark randomised trials anchor the topic: the Ocular Hypertension Treatment Study showed that lowering pressure in high-risk ocular hypertension delayed or prevented onset of open-angle glaucoma (Kass 2002); the Early Manifest Glaucoma Trial demonstrated that pressure reduction slowed progression in newly detected disease (Heijl 2002); and the Collaborative Initial Glaucoma Treatment Study compared initial medical versus surgical pressure-lowering strategies (Lichter 2001). Together they established intraocular pressure as the modifiable target for which the strongest randomised evidence exists.

History

For much of its history open-angle glaucoma was equated with raised pressure, but the recognition of normal-tension cases and of pressure-tolerant eyes shifted the concept toward an optic neuropathy with pressure as one risk factor. The cluster of randomised trials around the turn of the millennium provided the first high-quality evidence that pressure lowering changes the disease course, reframing both research and the understanding of causation (Kass 2002; Heijl 2002).

Debates

Is intraocular pressure the cause of open-angle glaucoma or one risk factor among several?: The existence of normal-tension glaucoma and of ocular hypertension without damage shows that pressure alone neither defines nor fully explains the disease, prompting interest in vascular and structural contributors while pressure remains the only target with strong randomised evidence.

Key figures

Robert N. Weinreb
Michael A. Kass
Anders Heijl
Paul R. Lichter

Seminal works

kass-2002
heijl-2002
lichter-2001
weinreb-2014

Frequently asked questions

Why is open-angle glaucoma often called a 'silent' disease?: Vision loss typically begins in the peripheral field and progresses slowly while central vision is preserved until late, so many people are unaware of damage until a substantial part of the visual field has already been lost.
Can someone have open-angle glaucoma with normal eye pressure?: Yes. In normal-tension glaucoma the characteristic optic nerve and visual field damage occurs even though intraocular pressure stays within the statistically normal range, which is why glaucoma is defined by optic nerve damage rather than pressure alone.