What causes glaucoma?

Glaucoma is normally due to raised pressure within the eye (intraocular pressure) due to an imbalance between the production and drainage of fluid. The

increased pressure in the eye puts strain on the optic nerve, which may result in loss of vision.

There are two main types of glaucoma:

  1. Primary open angle glaucoma (POAG)
  2. Primary angle closure glaucoma (PACG)

1 Primary open angle glaucoma (POAG)

POAG is the most common type of glaucoma. In Scotland, POAG affects 2% of of people over age of 40 and 10% of those over the age of 75. POAG is more common with increasing age, in those with a family history of glaucoma, short sight (myopia), diabetes or poor circulation. POAG may also be a side effect of medications such as steroids.

Unfortunately, many people with POAG are unaware they are affected until they have vision problems.

2 Primary angle closure glaucoma (PACG)

In Scotland, PACG is less common than POAG, affecting about 2 in 1000 people aged over 40 years, and it tends to occur in people who are long-sighted (hypermetropia). Interestingly, PACG is much more common in China and in people of East Asian origin.

Although rarer, PACG is a more aggressive form of glaucoma than POAG, with a higher risk of blindness.

Some people with PACG experience a suddenly painful red eye due to very high intraocular pressure but most have no symptoms until irreversible visual loss has occurred.

Tests for glaucoma include:

  1. Measurement of intraocular pressure
  2. Measurement of corneal thickness
  3. Examination of the eye’s drainage channels (gonioscopy)
  4. Visual fields
  5. Examination of the optic disc
  6. Measurement of the optic nerve (optical coherence tomography or OCT).