What is glaucoma?

Left untreated, glaucoma can cause vision loss and may eventually progress to blindness.

Glaucoma is the name given to a group of conditions that damage the optic nerve. This is 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.

It is a complex disease with many different subtypes and treatment options. At present, there is no cure for glaucoma.

Who is at risk?

The following factors can increase the risk of developing glaucoma:

  • a family history of glaucoma;

  • high eye pressure;

  • aged over 50;

  • African or Asian descent;

  • diabetes;

  • short or long sighted;

  • have had a prolonged course of cortisone (steroid) medication;

  • migraines;

  • undergone eye operation or eye injury;

  • high or low blood pressure; and

  • obstructive sleep apnoea.

A regular eye examination with your optometrist is recommended, usually every two years. If your optometrist suspects glaucoma, you will be referred to an ophthalmologist for further investigation. This usually involves a series of tests to assess the optic nerve for signs of damage and check for any signs of vision loss.

What causes glaucoma?

The majority of cases result from elevated pressure inside the eye – this pressure is also known as intraocular pressure (IOP). However, trauma to the eye and reduced blood flow around the optic nerve can also lead to glaucoma.

The Aqueous humour is the name of the watery fluid in the anterior part of the eye, between the cornea (protective window at the front of your eye) and the lens which sits just behind the iris, the coloured part of the eye.

In healthy eyes, the rate of production of aqueous humour 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, which sits in the ‘drainage angle’ between the iris and the cornea.

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.

Common types of glaucoma

There are two main types of glaucoma that are associated with increased IOP.

1. Primary open-angle glaucoma

This is the most common type of glaucoma. 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 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. For this reason, regular eye checks are needed to detect open-angle glaucoma early.

2. Acute angle-closure glaucoma

Also known as acute or narrow-angle glaucoma. This is a more severe, less common form and 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.

Other types of glaucoma

Normal-tension glaucoma

Optic nerve damage also occurs in people with ‘normal’ eye pressure – a condition known as normal-tension glaucoma. It is not understood why the optic nerve is more susceptible to damage in people with normal-tension glaucoma, however researchers suspect reduced blood flow around the optic nerve may be involved. 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

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).

Childhood glaucoma

Children can also develop or be born with glaucoma. Once again there is a complex series of different subtypes all requiring early diagnosis and treatment. Your paediatric ophthalmologist will be able to give you more information about this specialised sub-group of glaucoma.

Mia Rivera