Glaucoma is caused by a blockage in part of the eye. This prevents fluid draining out of the eye, and increases pressure in the eye, called intraocular pressure.
How the eye works
The eyeball is filled with a watery substance called aqueous humour, which creates pressure in the eye to give it shape. In healthy eyes, this fluid constantly flows in and out of the eye. It drains back into the bloodstream at the same rate that it is produced to maintain the correct pressure.
Glaucoma occurs when the drainage tubes (trabecular meshwork) within the eye become slightly blocked, preventing the aqueous humour from draining properly. An obstruction within the eye, such as a blood vessel blocking the trabecular meshwork, can also prevent fluid from draining properly.
When the fluid cannot drain properly, the pressure in the eye builds up and can damage the optic nerve, which is the nerve that connects the eye to the brain, and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).
It is often unclear why the drainage tubes become blocked or why other parts of the eye obstruct the tubes.
Risk factors
There are various factors that can increase your risk of developing glaucoma. These are explained below.
- Age: glaucoma becomes more likely as you get older. In the UK, chronic open-angle glaucoma affects 1 to 2 people in every 100 who are over 40 years old, and 4 to 5 people in every 100 who are over 80 years old.
- Ethnic origin: people of African or Afro-Caribbean origin are at increased risk of developing chronic open-angle glaucoma. People of Asian origin are at increased risk of developing acute angle-closure glaucoma.
- Short sightedness (myopia): people who are short-sighted are more likely to develop chronic open-angle glaucoma.
- Ocular hypertension (OHT - raised pressure in the eye): people with OHT are at increased risk of developing chronic open-angle glaucoma. Your optometrist will be able to diagnose OHT (see Glaucoma - diagnosis).
- Family history: if you have a close relative, such as a parent, brother or sister who has glaucoma, you are at increased risk of developing the condition yourself. You should therefore have regular eye tests to monitor the condition of your eyes.
- Medical history: people with diabetes, which is a condition caused by too much glucose in the blood, may be at increased risk of developing glaucoma.
