Causes of glaucoma 

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's 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 (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's often unclear why the drainage tubes become blocked or why other parts of the eye obstruct the tubes.

Increased risk 

There are a number of things that can increase your risk of developing glaucoma:

  • age (glaucoma becomes more likely as you get older) – in the UK, chronic open-angle glaucoma affects up to two in every 100 people over 40 years old and around five in every 100 people over 80 years old
  • ethnic origin – people of African or Afro-Caribbean origin are at increased risk of developing chronic open-angle glaucoma and 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) – your optometrist will be able to diagnose OHT (see diagnosing glaucoma), which increases your risk of developing chronic open-angle glaucoma
  • 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
  • medical history  people with diabetes may be at increased risk of developing glaucoma



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Pseudoexfoliation glaucoma

A relatively common cause of secondary glaucoma is known as pseudoexfoliation glaucoma. This type of glaucoma is caused by the body producing abnormal protein fibres, which can block the flow of fluid out of the eye, leading to glaucoma.

The causes of pseudoexfoliation glaucoma are unclear but most experts think that it is a genetic condition. Pseudoexfoliation glaucoma is treated in the same way as primary glaucoma.

Page last reviewed: 13/08/2014

Next review due: 13/08/2016