What is glaucoma?

Applanation tonometry test for eye pressure.
Applanation tonometry test for eye pressure.

The term “glaucoma” refers to a variety of conditions that share certain characteristics.

These are: 

  • Damage to the optic nerve with a “glaucomatous” appearance
  • Visual field loss (as such, glaucoma is a leading cause of blindness)
  • The presence of raised pressure within the eyeball (intraocular pressure) as a risk factor (although glaucoma may still occur in eyes with normal pressure)

To be diagnosed with glaucoma, a person must display at least two of the above features.

Those with only high intraocular pressure are followed up regularly, because some (not all) may go on to develop glaucoma at a later stage.

There are different ways in which glaucoma can be classified. The different classifications take into account various factors, including the age of onset, the speed of onset, the underlying mechanism, and other associated problems in the eye or body. 

The main ways of classifying glaucoma are as follows:

  • Open-angle vs. angle-closure glaucoma (based on the mechanism affecting the drainage of fluid from the eye)
  • Primary vs. secondary glaucoma (based on whether a factor contributing to the rise in intraocular pressure can be identified)
  • Congenital or acquired glaucoma (based on whether glaucoma is present at birth or whether it presents in adulthood)

The type of glaucoma that is most common in people of both European and African ethnic origin is primary open-angle glaucoma (POAG) – a progressive, chronic condition and a leading cause of blindness.

Reviewed by ophthalmologist Dr Tshilidzi van der Lecq. MBChB (UCT), Mmed (Ophth), FC Ophth (SA). March 2018.

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