What is the difference between open-angle and angle-closure glaucoma?

In open-angle glaucoma, the drainage angle appears open but the trabecular meshwork has reduced efficiency, causing gradual IOP elevation with no symptoms until late stage. In angle-closure, the iris physically blocks the drainage angle, which can occur suddenly (acute) with severe pain or gradually (chronic).

Can someone have 20/20 vision and still have glaucoma?

Yes. Glaucoma initially damages peripheral vision, which is not measured by standard visual acuity tests. A patient can have 20/20 central acuity with severe visual field loss. This is why glaucoma is often called the 'silent thief of sight.' Regular comprehensive eye exams with visual field testing are essential for detection.

What is the normal range for intraocular pressure?

Normal IOP ranges from 10-21 mmHg, with an average of about 15.5 mmHg. However, IOP above 21 mmHg does not automatically mean glaucoma (ocular hypertension), and glaucoma can occur with IOP below 21 mmHg (normal-tension glaucoma). IOP is just one risk factor among many.

Glaucoma: Types & Management for ABO

What Is Glaucoma?

Glaucoma is a group of progressive optic neuropathies characterized by damage to the optic nerve head (optic disc) and corresponding visual field loss. It is the leading cause of irreversible blindness worldwide. While elevated intraocular pressure (IOP) is the primary risk factor, glaucoma can occur at any IOP level.

Types of Glaucoma

Primary Open-Angle Glaucoma (POAG)

The most common form (~90% of cases). The drainage angle appears open and normal, but the trabecular meshwork has reduced outflow efficiency. Key characteristics:

Gradual onset with no symptoms until significant field loss occurs
Typically bilateral but may be asymmetric
Risk factors: age over 40, family history, African descent, high IOP, thin cornea
Usually diagnosed through routine eye exams

Normal-Tension Glaucoma (NTG)

A subtype of POAG where optic nerve damage occurs despite IOP consistently within the normal range (below 21 mmHg). The optic nerve may be unusually susceptible to pressure or have compromised blood supply.

Angle-Closure Glaucoma

The iris blocks the trabecular meshwork, preventing aqueous drainage. Can be:

Acute: Sudden, painful closure causing IOP spike to 40-80 mmHg. Medical emergency with symptoms including severe eye pain, headache, nausea, halos around lights, and red eye.
Chronic: Gradual, asymptomatic narrowing and periodic partial closures

Open-angle glaucoma is painless and progressive. Patients lose peripheral vision first and may not notice until significant damage has occurred. Angle-closure can be an acute emergency with sudden severe pain. These are fundamentally different presentations of the same disease family.

How Glaucoma Damages Vision

Elevated IOP damages retinal ganglion cell axons at the lamina cribrosa (the sieve-like region where the optic nerve exits the eye). The characteristic changes include:

Optic disc cupping: Enlargement of the cup-to-disc ratio as nerve fibers are lost
Nerve fiber layer thinning: Visible on OCT scans
Visual field defects: Typically begin as paracentral scotomas or nasal steps, progressing to arcuate defects, and eventually tunnel vision

Central acuity is usually preserved until late-stage disease, which is why patients may have 20/20 acuity but severe visual field loss.

IOP Measurement

Method	Principle	Notes
Goldmann applanation	Measures force to flatten cornea	Gold standard, affected by corneal thickness
Non-contact (air puff)	Air pulse flattens cornea	Screening tool, less accurate
Tonopen	Electronic applanation	Portable, good for irregular corneas
iCare (rebound)	Probe bounces off cornea	No anesthetic needed, good for children

Treatment Approaches

Treatment focuses on lowering IOP, even in normal-tension glaucoma:

Medications: Topical eye drops that reduce aqueous production or increase drainage (prostaglandin analogs, beta-blockers, alpha agonists, carbonic anhydrase inhibitors)
Laser: Selective laser trabeculoplasty (SLT) for open-angle; laser peripheral iridotomy (LPI) for angle-closure
Surgery: Trabeculectomy, tube shunts, or micro-invasive glaucoma surgery (MIGS) for cases unresponsive to drops and laser

Glaucoma patients on prostaglandin drops (like latanoprost) may notice their eyelashes becoming longer and thicker, and their iris color may darken over time. These cosmetic side effects are harmless but can be surprising. Being aware of this helps you reassure patients during dispensing.

Equating elevated IOP with glaucoma. Not everyone with high IOP has glaucoma (ocular hypertension), and not everyone with glaucoma has high IOP (normal-tension glaucoma). Glaucoma is diagnosed by optic nerve damage and visual field loss, not by IOP alone.

Key Takeaways

Glaucoma is progressive optic nerve damage with visual field loss, often linked to elevated IOP
Open-angle (90% of cases) is painless and gradual; angle-closure can be an acute emergency
Peripheral vision is lost first; central acuity is preserved until late stages
Treatment focuses on lowering IOP through drops, laser, or surgery
High IOP alone is not glaucoma; optic nerve damage is the defining feature