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Glaucoma is the name given to a group of conditions that damage the optic nerve (the nerve at the back of the eye that transmits visual signals to the brain). Nerve damage is permanent and leads to irreversible vision loss. If left untreated, this vision loss may eventually progress to blindness.
The majority of cases result from elevated pressure inside the eye – this pressure is also known as intraocular pressure or IOP. However, trauma to the eye and reduced blood flow can also lead to glaucoma.
In healthy eyes, the rate of fluid (aqueous humour) production equals the rate it flows out of the eye to maintain a stable intraocular pressure. Aqueous humour flows out of the eye through a spongy tissue known as the trabecular meshwork. The trabecular meshwork sits in the ‘drainage angle’ between the iris (the coloured part of the eye) and the cornea (the clear, protective outer layer).
If the outward flow of aqueous humour is reduced or blocked, a build-up of fluid occurs and this leads to an increase in IOP. The higher the intraocular pressure, the more likely a person is to develop glaucoma. However, high IOP in itself is not sufficient to confirm a diagnosis of glaucoma – signs of optic nerve damage and visual field loss must also be present.
There are two main types of glaucoma that are associated with increased IOP.
Also known as chronic glaucoma, this condition accounts for approximately 90% of cases of glaucoma.1 It results when the trabecular meshwork is partially blocked, but the drainage angle is still open. This causes a gradual rise in IOP that slowly leads to peripheral (side) vision loss, before eventually affecting central vision. There are often no early signs or symptoms, meaning many people are unaware they have glaucoma until the advanced stages of the disease (which is why chronic glaucoma is commonly referred to as ‘the sneak thief of sight’). For this reason, regular eye checks are needed to catch open-angle glaucoma early.
Also known as acute or narrow-angle glaucoma, this more severe, less common form of glaucoma is characterised by the sudden closure of the drainage angle. It results in the complete blockage of the trabecular meshwork and a rapid increase in eye pressure that causes vision to quickly deteriorate. Angle-closure glaucoma is considered a medical emergency that requires urgent treatment to prevent sight loss.
Warning signs of acute angle-closure glaucoma include sudden changes in vision, eye redness, eye pain, nausea and severe headaches.
Optic nerve damage also occurs in people with ‘normal’ eye pressure – a condition known as normal-tension glaucoma. Individuals with a history of migraine and Raynaud’s phenomenon are at higher risk of developing this condition. Although it is not understood why the optic nerve is more susceptible to damage in people with normal-tension glaucoma, researchers suspect reduced blood flow may be involved.2 Similarly to open-angle glaucoma, people often have no symptoms until the advanced stages of the disease. Regular eye checks are essential as they are the only way to catch the disease early, allowing people to start treatment before vision is seriously compromised.
Secondary glaucoma is any form of glaucoma where the increase in IOP is due to a known cause (e.g. injury, diseases affecting the eyes or entire body, certain medications).3 Examples include traumatic glaucoma, uveitic glaucoma and pigmentary glaucoma.
Childhood glaucoma is categorised into three types, based on the age of onset.4
Childhood glaucoma is associated with increased IOP and may be classed as primary or secondary.4,5
Symptoms of childhood glaucoma include enlarged eyes, light sensitivity, watery eyes, large teardrops, and cloudy or white corneas.
If you are over 50 (or over 40 and have a higher risk of developing glaucoma), a thorough eye check is recommended every one to two years. If your GP or optometrist suspects glaucoma, you will be referred to an ophthalmologist for further investigation. This will involve a series of tests to assess the optic nerve for signs of damage and check for any signs of vision loss.
The information on this page is general in nature. All medical and surgical procedures have potential benefits and risks. Consult your ophthalmologist for specific medical advice.
Date last reviewed: 2023-08-07 | Date for next review: 2025-08-07