The simple test that can save you from blindness

A simple test can reveal the early stages of glaucoma.
Jason Oxenham

A simple test can reveal the early stages of glaucoma.

It is glaucoma awareness month - a time to get your eyes tested, and to encourage your loved ones to do the same.

Glaucoma is the leading cause of blindness in New Zealand, with about 2 per cent of people over 40 years old being affected. It has massive consequences worldwide, with 64 million affected at present – that's 4.5 per cent of the entire global population – but an estimated doubling of that number over the next 25 years.

The good news is that it is entirely preventable. If glaucoma is detected and treated before there is significant loss of vision, your sight can be preserved. The implications of that are obviously huge – loss of vision leads to loss of independence, which for many of us is a horrifying thought.

Although there are several sub-groups of glaucoma, the underlying process is similar. There is gradual damage to the optic nerve, leading to a loss of vision.

The optic nerve runs from the back of the eye, to the brain. Its role is to process images we see, and send them to the brain so we can understand them. Without the optic nerve, we wouldn't be able to see anything at all.

In glaucoma, the fibres within the optic nerve gradually die, leading to loss of function and therefore loss of vision. Unfortunately, damage to this important nerve is irreversible. The main types of glaucoma are:

* Chronic open angle glaucoma – this is by far the most common type, and is usually just referred to as "glaucoma"; this is the type I will talk about here

* Normal tension glaucoma – in this condition, the optic nerve is damaged, even though eye pressures are normal

* Acute open angle glaucoma – this is a much more sudden process, and results in an "eye emergency"; if it is treated quickly, vision can usually be preserved

* Secondary glaucoma – this type of glaucoma develops as a result of some other problem in the eye, e.g. trauma

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* Congenital glaucoma – although rare, some people will be born with glaucoma, requiring detection and treatment in early childhood to avoid blindness.

In chronic open angle glaucoma (COAG), the damage to the optic nerve is caused by a build-up of pressure in the eye. It is not known quite why this happens, but there is a gradual blockage of the drainage system in the eye, creating a rise in pressure in the eyeball, and hence on the optic nerve itself.

COAG is a gradual process, leading to slow loss of vision. As the peripheral (or outside) vision is affected first, it is often not detected until it is quite advanced, especially in older people who will often put it down to "ageing eyes".

Usually COAG will present with no symptoms, hence the importance of getting regular checkups. If you do notice anything, it is likely to be a blurring of your peripheral vision, or "blind spots" developing over time.

Risk factors include:

* Age – although glaucoma can affect anyone 40 or over, it is much more common as you get older

* Family history – if you have a close relative with glaucoma, you are 3-10 times more likely to develop it yourself

* Ethnicity – glaucoma is more common in certain races, e.g. African Americans

* Pressure – the higher the pressure in your eye, the greater the risk of developing glaucoma; your optometrist can measure the pressure in your eye with a simple test that only takes a few moments; this "intraocular" pressure is not the same as blood pressure.

It is recommended that everyone over 40 gets a check for glaucoma every five years, and more frequently as you get older. Although you may have to pay for an eye check, the long-term benefits are huge. If detected, glaucoma is nearly always completely treatable, preserving eyesight you might otherwise have lost.

The majority of people with glaucoma will use eye drops to treat it. Sometimes this will not be enough to control the pressures within the eye, and either tablets or surgery will be recommended. For more information or support, visit glaucoma.org.nz.

Cathy Stephenson is a GP and medical forensic examiner. 

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