HOME arrow LATEST NEWS arrow Waikato Times Feature: Early glaucoma detection important
Waikato Times Feature: Early glaucoma detection important

Published in the Waikato times feature April 2008

Glaucoma is a term commonly heard in eye clinics and doctors offices, but what is it exactly? Glaucoma is the name given to a group of related diseases where the optic nerve is being damaged.
It is the second most common cause of blindness, affecting two per cent of the population over 40.
When we look at an object, the picture is carried from the eye to the brain by the optic nerve. This nerve is like a telephone cable - it contains many wires, each carrying a message, which join together to provide side vision, as well as sharp, central reading vision.

The eye has pressure within it to keep it inflated, like a balloon. When increased pressure within the eye causes damage to some of these wires, messages are not sent to the brain, and blind areas in the field of vision will develop. This is glaucoma.

The patient seldom notices these peripheral blind areas until considerable damage has occurred; if the entire nerve is destroyed, blindness results. However, blindness rarely occurs when glaucoma is diagnosed before there is extensive damage to the nerve, because glaucoma is a treatable condition.

Dr James Stewart of the Hamilton Eye Clinic is a general ophthalmologist and glaucoma specialist, and knows the damage glaucoma can cause when it goes untreated. "We have patients come in who are almost completely blind, and are still driving - they have huge gaps in their vision, but don't notice something is wrong until they start tripping over furniture or having car accidents," he says.

Glaucoma is more common as people get older, but people of any age can get it, including children and babies. Glaucoma New Zealand recommends "45 + 5". It suggests your first glaucoma check when you turn 45, and every five years after that. Over 60, a check is recommended every three years. An initial assessment can be done by an optometrist, and if glaucoma risk factors are present they can recommend that the patient be seen more often.

If glaucoma is present, the patient is referred to an ophthalmologist, who does an initial glaucoma assessment. This involves a full eye exam, a visual field test, measurement of corneal thickness, pictures of the optic nerve, and an OCT (optical coherence tomography) scan, which measures the amount of nerve tissue at the back of the eye.
Many risk factors increase the chance of damage, most commonly a history of glaucoma in the family; others include diabetes, migraine, arteriosclerosis and anaemia.
Glaucoma is usually treated with eye drops, used to lower the pressure in the eye by assisting outflow of fluid from the eye, or by decreasing the inflow of fluid. Dr Stewart says there is more to glaucoma than eye pressure, but at the moment, the only factor doctors can treat is eye pressure. Laser treatment may be used, and occasionally, tablets are prescribed. There is surgery available, but is usually reserved for those patients who are not responding well to other treatments. "Glaucoma is a lifelong condition," Dr Stewart says. "If you are doing well you need to be checked out every six months, and have visual field tests done once a year." While the effects of glaucoma can be dramatic, vigilance and regular eye checks can almost eliminate blindness resulting from the disease. "When diagnosed early, glaucoma is almost always controllable with ongoing treatment," Dr Stewart says. For more information, go to www.glaucoma.org.nz

How do glaucoma tests work?


To test for glaucoma, an orthoptist will perform a range of tests. Hamilton Eye Clinic's Sue Bull put Life etc journalist Anne Clarke through her paces with both a visual field test and OCT scan.


A visual field test is designed to map a person's visual field by documenting the extent of peripheral vision.
As most glaucoma patients know, the test consists of sitting in front of a concave dome with a target in the centre, and the eye that is not being tested is covered. The patient responds by pressing a button every time a flash of light is perceived. The computer then automatically maps and calculates the patient's visual field.
Such intense and repeated decision-making over five minutes for each eye is hard work; you are quite tired afterwards.
The field report generated by modern visual field devices includes a wealth of information, all of which can be useful to the doctor interpreting the results, such as false positives (the number of times the patient pushes the button when, in reality, a light source is not illuminated), and false negatives (the number of times the patient fails to push the button when, in reality, there is a light source illuminated).
The visual field map is the final basic report indicating the patient's visual field anywhere from the central 10 degrees all the way out to the farthest reaches of the field at 90 degrees. Altered patterns in the field map from reliable patient testing are often extremely useful in the diagnosis of ocular or neurological disorders.


This advanced technology uses light to measure the thickness and amount of optic nerve tissue at the back of the eye, which is what is lost in glaucoma. A fine laser sends light into the eye which is carefully analysed as it is reflected back out of the eye by a sophisticated computer. This amazing technology can measure thickness down to a thousandth of a millimetre. The measurements of nerve thickness are classified as normal or otherwise, and in particular are compared test to test to establish if there is further progression of glaucoma with loss of more nerve tissue. For the patient, having an OCT scan is easy and not particularly unpleasant - rather like having a photograph taken.