What Is Glaucoma? Symptoms, Diagnosis and Treatment

What Is Glaucoma?

Glaucoma is a group of eye diseases that can progressively damage the optic nerve, which connects the eye to the brain.

As optic nerve damage progresses, permanent areas of visual-field loss can develop. Untreated glaucoma can ultimately lead to severe visual impairment and blindness.

Elevated intraocular pressure is one of the most important modifiable risk factors for glaucoma, but glaucoma is not simply a disease of high eye pressure.

Are High Eye Pressure and Glaucoma the Same?

No.

Intraocular pressure refers to pressure within the eye. Glaucoma refers to a group of disorders characterised by typical optic nerve damage and associated visual-field loss.

Elevated intraocular pressure without corresponding glaucomatous optic nerve or visual-field damage may be described as ocular hypertension.

Conversely, glaucoma can occur when measured intraocular pressure remains within a statistically normal range.

What Are the Symptoms of Glaucoma?

The most common form, open-angle glaucoma, generally causes no noticeable symptoms during its early stages.

As damage progresses, vision is usually lost gradually, often beginning in the peripheral visual field.

Later symptoms may include narrowing of peripheral vision, blind spots and eventually impairment of central vision in advanced disease.

Eye pain and redness are not typical early features of chronic open-angle glaucoma. They are particularly important when acute angle closure is suspected.

What Are the Types of Glaucoma?

Major categories include:

• Primary open-angle glaucoma
• Normal-tension glaucoma
• Primary angle closure and angle-closure glaucoma
• Secondary glaucomas
• Congenital and childhood glaucomas

Secondary glaucoma can develop following eye trauma, inflammation, other ocular diseases or exposure to medicines such as corticosteroids.

What Is Open-Angle Glaucoma?

Primary open-angle glaucoma is one of the most common forms of glaucoma.

The drainage angle remains anatomically open, but resistance to aqueous humour outflow through the trabecular meshwork can increase.

Intraocular pressure may be elevated, but the diagnosis of glaucoma is not based on pressure alone.

The condition usually progresses slowly and often causes no pain or obvious visual symptoms in its early stages.

What Is Normal-Tension Glaucoma?

In normal-tension glaucoma, characteristic progressive optic nerve damage and visual-field loss occur despite intraocular pressure not being conventionally elevated.

This demonstrates why a normal eye-pressure measurement does not by itself exclude glaucoma.

Lowering intraocular pressure below an individualised target level can still help slow progression.

What Is Angle-Closure Glaucoma?

Angle closure occurs when the iris narrows or blocks the drainage angle through which aqueous humour normally leaves the eye.

Some forms develop gradually, but acute angle closure can cause a rapid increase in intraocular pressure and represents an ophthalmic emergency.

Symptoms can include severe eye pain, redness, blurred vision, coloured halos around lights, headache, nausea and vomiting.

What Are the Risk Factors for Glaucoma?

Risk factors vary by glaucoma subtype but can include:

• Elevated intraocular pressure
• Increasing age
• A first-degree relative with glaucoma
• A thin central cornea
• Certain refractive errors such as high myopia
• Prolonged or high-dose corticosteroid exposure
• Certain eye injuries and ocular disorders

The appropriate examination interval should be individualised according to age, family history, ocular anatomy, intraocular pressure and other risk factors.

How Is Glaucoma Diagnosed?

Measuring eye pressure alone is not sufficient to diagnose or exclude glaucoma.

Assessment can include:

• Tonometry: measurement of intraocular pressure
• Optic nerve examination: assessment for characteristic structural damage
• Optical coherence tomography: evaluation of retinal nerve fibre and ganglion-cell layers
• Visual-field testing: assessment of functional visual-field loss
• Gonioscopy: examination of whether the drainage angle is open or narrow
• Pachymetry: measurement of central corneal thickness
• Dilated optic nerve and retinal examination

Repeated OCT and visual-field testing may be required to determine whether glaucoma is progressing over time.

Why Are OCT and Visual Field Tests Used?

Optical coherence tomography (OCT) can provide high-resolution measurements of the retinal nerve fibre layer and retinal ganglion-cell structures.

Visual-field testing assesses functional loss in central and peripheral vision.

The tests are complementary rather than interchangeable: one provides structural information and the other measures functional vision.

How Is Glaucoma Treated?

The goal of glaucoma treatment is to preserve remaining vision and reduce the rate of further optic nerve damage.

The principal evidence-based treatment is lowering intraocular pressure to an appropriate individualised target.

Treatment options include:

• Prescription eye drops
• Laser procedures
• Filtering surgery such as trabeculectomy
• Glaucoma drainage devices
• Minimally invasive glaucoma surgery in selected patients

Treatment is individualised according to glaucoma subtype, severity, target intraocular pressure, other ocular conditions and the patient's ability to use treatment consistently.

How Do Glaucoma Eye Drops Work?

Glaucoma medicines lower intraocular pressure by reducing aqueous humour production or increasing fluid outflow.

Prostaglandin analogues, beta blockers, carbonic anhydrase inhibitors and other drug classes can be used depending on the patient.

Prescribed drops should be used consistently. Treatment should not be stopped simply because the eye feels normal or because the patient does not notice a change in vision.

What Is Laser Treatment for Glaucoma?

Selective laser trabeculoplasty (SLT) can be used in suitable patients with open-angle glaucoma or ocular hypertension to improve aqueous outflow through the trabecular meshwork.

Laser treatment is not reserved only for patients in whom eye drops have failed. Current guidance allows SLT to be considered as an initial treatment option in selected open-angle glaucoma and ocular-hypertension patients.

For angle-closure disease, a different procedure known as laser peripheral iridotomy may be indicated.

When Is Glaucoma Surgery Needed?

Surgery can be considered when medicines or laser treatment do not achieve sufficient pressure reduction, when glaucoma continues to progress despite treatment or when advanced disease requires a very low target pressure.

Trabeculectomy, glaucoma drainage implants and minimally invasive glaucoma procedures are among the available surgical approaches.

The objective of surgery is not to reverse existing optic nerve damage but to lower intraocular pressure sufficiently to help protect the remaining vision.

Can Vision Lost From Glaucoma Be Restored?

Vision lost because of permanent glaucomatous optic nerve damage generally cannot currently be restored.

The objective of treatment is therefore to preserve remaining vision and slow further progression.

This is why early diagnosis is important.

Which Glaucoma Symptoms Are an Emergency?

Frequently Asked Questions

References

1. Academic Hospital. Glaucoma
2. National Eye Institute. Glaucoma
3. National Institute for Health and Care Excellence. Glaucoma: Diagnosis and Management