Glaucoma: Types, Silent Symptoms, Screening and Treatment

Glaucoma is a group of eye diseases that damage the optic nerve, the cable of more than a million nerve fibres that carries visual information from the eye to the brain. Once those fibres are lost, they do not grow back, so vision lost to glaucoma is permanent. According to the World Health Organization, glaucoma is one of the leading causes of irreversible blindness worldwide.

What makes glaucoma so dangerous is that the most common form causes no pain and no noticeable symptoms until a large part of the nerve is already damaged. The encouraging side is that early detection and consistent treatment can slow or stop progression in the great majority of people, allowing them to keep useful sight for life. This guide explains the types of glaucoma, the role of eye pressure, how screening works, the main treatments and the warning signs of an emergency attack.

How glaucoma damages the eye

The front of the eye is filled with a clear fluid called aqueous humour. It is constantly produced behind the iris, flows through the pupil and drains out through a spongy tissue called the trabecular meshwork, located in the drainage angle where the iris meets the cornea. A healthy balance between production and drainage keeps the eye pressure within a stable range.

When drainage is reduced, pressure tends to rise. Higher pressure stresses the optic nerve head at the back of the eye, and blood flow to the nerve may also be impaired. Over time, nerve fibres die and the optic disc develops a characteristic hollowed appearance known as cupping. The pattern of vision loss follows: usually patchy blind spots in the mid-peripheral field that slowly merge and spread inward. For background, see our guide to how vision works.

Types of glaucoma

Primary open-angle glaucoma

This is the most common form in Europe, North America and Africa. The drainage angle looks open, but the meshwork drains fluid less efficiently. Pressure rises gradually, damage builds up over years and both eyes are usually affected, often unequally. Because the brain fills in gaps and the other eye compensates, people rarely notice anything until the disease is advanced.

Angle-closure glaucoma

Here the iris sits too close to the drainage angle and physically blocks it. This is more common in people of East Asian descent, in women, in people with farsightedness (hyperopia) and with increasing age, as the natural lens thickens. Angle closure can be chronic and silent, or it can happen suddenly as an acute attack, described below.

Normal-tension glaucoma

Some people develop typical optic nerve damage even though their measured pressure is always within the statistically normal range, roughly 10 to 21 mmHg. Their nerves appear unusually vulnerable, possibly due to blood flow problems, low blood pressure at night or structural factors. Lowering the pressure further still helps: a landmark collaborative study showed that reducing pressure by about 30 percent slowed progression in many patients.

Other types

• Secondary glaucoma: caused by another condition or treatment, such as eye injury, inflammation (see our uveitis guide), long-term steroid use, pigment dispersion, pseudoexfoliation or advanced diabetic eye disease.
• Congenital and childhood glaucoma: rare; signs include a large cloudy cornea, watering and light sensitivity in a baby.

Eye pressure: important, but not the whole story

Intraocular pressure is measured in millimetres of mercury (mmHg). Pressure above 21 mmHg is considered raised, but this does not automatically mean glaucoma. Some people have high pressure for years without nerve damage; this is called ocular hypertension. Large trials such as the Ocular Hypertension Treatment Study showed that treating raised pressure in selected people reduces their risk of developing glaucoma, so the decision to treat depends on overall risk.

Corneal thickness also matters. A thin cornea can make pressure readings appear lower than they truly are and is itself a risk factor, while a thick cornea can make readings appear higher. This is why eye doctors combine several measurements instead of relying on a single number.

Why glaucoma is called the silent thief of sight

In open-angle and normal-tension glaucoma there is no pain, no redness and central reading vision usually remains sharp until late. Side vision is lost first, and the brain is remarkably good at hiding small gaps. Many people only discover the problem when they bump into objects, miss cars approaching from the side or fail a driving field test. By then, a substantial share of the optic nerve may already be lost. That is why glaucoma is detected far more often by routine eye exams than by symptoms.

Risk factors and who should be screened

• Age over 40, with risk rising further after 60.
• Family history: having a parent or sibling with glaucoma increases risk considerably. Our article on family history and eye disease explains why relatives should be checked.
• Ancestry: people of African descent have a higher risk of open-angle glaucoma and tend to develop it earlier; people of East Asian descent have a higher risk of angle closure.
• High myopia (open-angle) or hyperopia (angle-closure).
• Raised eye pressure and thin corneas.
• Long-term steroid use in any form, including eye drops, inhalers and creams around the eyes.
• Diabetes, high or very low blood pressure, migraine and sleep apnoea have been associated with higher risk in some studies.
• Previous eye injury or eye surgery.

Professional bodies generally advise a baseline comprehensive eye exam around age 40 and regular checks thereafter, more often if you have risk factors. Your optometrist or ophthalmologist will set the interval; see how often to get an eye exam.

How glaucoma is diagnosed

No single test can confirm or exclude glaucoma. Diagnosis is based on putting several findings together:

1. Tonometry: measuring eye pressure, for example with a puff of air or a gentle probe after numbing drops.
2. Optic nerve examination: looking at the optic disc through a dilated pupil for cupping, thinning of the rim or small haemorrhages.
3. Optical coherence tomography (OCT): a painless scan that measures the thickness of the nerve fibre layer, able to detect thinning before field loss appears.
4. Visual field test (perimetry): you press a button when you see small lights appear in your peripheral vision, which maps blind spots.
5. Gonioscopy: a special mirrored contact lens shows whether the drainage angle is open or narrow.
6. Pachymetry: measuring corneal thickness.

Online peripheral vision checks, such as our peripheral vision test, can be educational but cannot detect early glaucoma and never replace professional testing.

Treatment options

All current treatments work by lowering eye pressure, even in normal-tension glaucoma. The doctor sets a target pressure for each person and adjusts treatment if tests show progression.

Eye drops

Drops are the most common first treatment. The main classes are prostaglandin analogues, which increase fluid outflow and are usually used once daily; beta-blockers and carbonic anhydrase inhibitors, which reduce fluid production; alpha agonists, which do both; and newer Rho kinase inhibitors, which act on the meshwork. Side effects vary by class and can include red eyes, stinging, darkening of the iris or eyelid skin, longer lashes, tiredness or breathing problems in susceptible people. Always tell your doctors about asthma, heart conditions and other medicines. The single most important factor is using the drops every day as prescribed; glaucoma does not cause symptoms when treatment is missed, which makes adherence hard.

Laser treatment

• Selective laser trabeculoplasty (SLT): a gentle laser treatment applied to the drainage meshwork to improve outflow. It takes a few minutes in the clinic. The UK LiGHT trial found SLT to be an effective first-line treatment for open-angle glaucoma and ocular hypertension, allowing many patients to stay drop-free for years. Its effect can wear off and it can be repeated.
• Laser peripheral iridotomy: a tiny opening is made in the iris to let fluid bypass the pupil, used to treat or prevent angle closure.
• Cyclophotocoagulation: laser that reduces fluid production, mainly for advanced or difficult cases.

Surgery

When drops and laser are not enough, surgery creates a new drainage route. Trabeculectomy forms a small flap and a reservoir (bleb) under the conjunctiva. Glaucoma drainage devices (tube shunts) channel fluid to a plate on the eye wall. Minimally invasive glaucoma surgery (MIGS) uses tiny stents or devices, often combined with cataract surgery, for mild to moderate disease. In angle-closure glaucoma, removing the natural lens can itself widen the angle. Each option has different benefits and risks that your surgeon will discuss.

Acute angle-closure glaucoma: an emergency

In an acute attack, the drainage angle closes suddenly and eye pressure can rise to very high levels within hours. Without urgent treatment, permanent vision loss can occur quickly. Attacks may be triggered by pupil dilation, for example in dim light, during stress or by certain medicines including some decongestants, antihistamines, antidepressants and dilating eye drops.

Living with glaucoma

Glaucoma is usually a lifelong condition that needs lifelong monitoring. Practical habits make a big difference:

• Use drops at the same time every day; link them to a routine such as brushing your teeth.
• Learn good drop technique and close the eye gently with light pressure on the inner corner for a minute afterwards to reduce absorption into the body.
• Keep every follow-up appointment, even when you feel fine.
• Tell relatives, because their risk is higher and they should be examined.
• Check driving regulations; some countries require you to report glaucoma affecting both eyes.
• If vision is already reduced, low-vision services can help; see our low vision guide.

When to see a doctor

Book a comprehensive eye exam if you are over 40 and have not had one recently, if a close relative has glaucoma, if you use long-term steroids, or if you notice you are bumping into things or missing objects at the side. People already diagnosed should report any change in vision or difficulty with drops.