About half of the people in New Zealand who have the eye disease glaucoma do not realise it, Dunedin opthalmologist Mary Jane Sime says.
Dr Sime said that while the disease, if picked up early, can be controlled to prevent irreversible sight loss, it cannot be cured.
"The problem is that it is a very silent disease, a little bit like blood pressure. You may not notice anything until it is very advanced and you have lost a lot of your peripheral field."
Effects which might be noticed were the loss of the peripheral vision which could mean that people had the experience of seeing something "pop up out of nowhere", something which could be quite dangerous for people driving who might suddenly see cyclists.
It was recommended that everyone from the age of 45 should have an eye examination for glaucoma every five years until they were 60 and then every three years after that.
Often people who found they needed reading glasses in their 40s would buy them from a shop without having their eye health checked.
Possibly some were nervous about having an eye check.
The eyes were a very sensitive area and some people might find it "a bit scary" having someone examine their eyes closely.
Some people might be concerned at the cost of an eye examination, but that had to be balanced against the risk of losing sight.
Costs for an eye examination vary, according to Glaucoma New Zealand, within the range of about $60 to $80.
Glaucoma examinations are carried out by optometrists and opthalmologists.
Once diagnosed, most cases could be controlled with the regular use of eye drops, but some patients presented with advanced glaucoma and it was difficult to get the pressure on the eye down low enough to prevent progression of the disease.
Laser treatment and surgery were the other options for treatment, Dr Sime said.
Sometimes, it could be hard to get patients to comply with the need to take eye drops regularly - "it's a bit of an unknown quantity".
Some became better at using the drops when they realised what the alternative treatments would be.
Today, there was a much wider range of drops available than there used to be, with fewer side effects, Dr Sime said.
Dr Sime is the guest speaker at a public meeting in Dunedin on August 28 at Mercure Hotel in Princes St, at 10am.
She will discuss the various types of glaucoma and the treatments available.
Dr Sime said the meeting would be of interest to people who had already been diagnosed with glaucoma and to anyone wishing to learn more about the disease.