Glaucoma: symptoms, risk factors and how it is tested

What glaucoma is

The optic nerve is the cable that carries what the eye sees to the brain. In glaucoma, the fibres of that nerve are slowly damaged. In most cases the cause is fluid pressure inside the eye that is higher than the nerve can tolerate, although glaucoma can also occur with normal pressure.

Nerve fibres that die are not replaced. Glaucoma is the leading cause of irreversible blindness in the world, and the reason is not that it cannot be treated. It is that so many people do not know they have it until it is advanced.

Why it is called the silent thief of sight

The most common type, open-angle glaucoma, develops over years with no pain, no redness and no blur. It takes side (peripheral) vision first, in patches that the other eye and the brain fill in. Central vision, which you use for reading and recognising faces, stays sharp until late. By the time someone notices that they are bumping into things or missing cars approaching from the side, a large part of the optic nerve has already been lost.

You can have 6/6 vision on the letter chart and still have glaucoma. Only an eye examination can find it early.

Who is at risk

Anyone can develop glaucoma. The risk is higher if you:

• are over 40, and it rises with each decade
• have a parent, brother or sister with glaucoma
• are of African descent. In people of African ancestry, glaucoma is more common, tends to start earlier and can progress faster.
• have raised eye pressure
• are very short-sighted
• have diabetes or high blood pressure
• have used steroid medication for a long time, including some eye drops, inhalers and creams
• have had a serious eye injury

If glaucoma runs in your family, tell your optometrist, and tell your relatives if you are diagnosed. Brothers, sisters and children should be tested.

The type that is an emergency

A less common form, acute angle-closure glaucoma, comes on suddenly when the drainage channel inside the eye becomes blocked and the pressure rises within hours.

Sudden severe eye pain, a red eye, blurred vision, halos or rainbow rings around lights, headache, and nausea or vomiting together are an emergency. Go to an emergency unit or an ophthalmologist immediately. Without treatment, sight can be lost within a day or two.

How glaucoma is tested

There is no single test. A diagnosis is built from several findings:

• Eye pressure. Measured with a quick puff of air or a small probe that briefly touches the numbed eye. It is painless.
• The optic nerve. The optometrist or ophthalmologist looks at the nerve at the back of the eye for the typical changes in shape.
• Visual field. A test in which you press a button when you see small lights, which maps any blind patches in your side vision.
• Scans and further measurements. A specialist may add a scan of the nerve fibre layer, a measurement of corneal thickness and an examination of the eye's drainage angle.

An optometrist's role is to check for signs of glaucoma as part of an eye test and to refer you if anything looks suspicious. The diagnosis is confirmed, and treatment is prescribed, by an ophthalmologist. Optometrist, ophthalmologist or optician? explains who does what.

How glaucoma is treated

All treatment works by lowering the pressure in the eye to a level the nerve can cope with.

• Eye drops, used every day, are the most common treatment. They only work if they are used exactly as prescribed, for life.
• Laser treatment improves the drainage of fluid and can reduce or replace the need for drops.
• Surgery creates a new drainage route when drops and laser are not enough.

Treatment does not bring back vision that has been lost. It protects what remains. That is why the stage at which glaucoma is found matters so much.

How often to be tested

• Under 40 with no risk factors: as part of a routine eye test every two years.
• 40 and over: every one to two years.
• Higher risk, such as a family history, African ancestry, diabetes or strong short-sightedness: every year, or as advised.

See how often you should have an eye test for the full schedule.

Start with a routine eye test

See Better brings the eye test to your home or workplace in Gauteng for R450. Tell the optometrist about any family history of glaucoma. If anything needs further investigation, you will be referred to an ophthalmologist.