Your Vision

What is Glaucoma?

Glaucoma refers to a group of eye diseases which result in vision loss and damage to the optic nerve due to increased pressure within the eye.  This increased pressure eventually causes injury to the nerve that interprets the “image” in vision resulting in irreversible loss of eyesight. In most instances glaucoma develops slowly with no noticeable sight loss for many years.  It has thus been referred to as the “sneak thief” of sight.

If left untreated, glaucoma can lead to vision loss and even to total blindness.  However, if glaucoma is diagnosed early and treatment started at an early stage, permanent vision loss can be prevented.


Glaucoma causes include elevated eye pressure (called intraocular pressure or IOP) due to the eye’s inability to drain fluid efficiently. If the drainage angle of the eye is blocked, excess fluid cannot flow out of the eye thus causing the fluid pressure within the eye to increase.


There are two main types of glaucoma, open-angle and closed-angle (angle-closure) glaucoma.

Open-angle glaucoma is the most common and is caused when there is a restriction in the natural outflow of fluid from the eye.  Causes include, amongst others, ageing, a family history of glaucoma, anatomical abnormalities and metabolic stresses of the optic nerve.

Angle-closure glaucoma is a rare form of the disease. In angle-closure glaucoma the iris bows forward, narrowing the angle that drains the eye and thus increasing the pressure within the eye.  Angle-closure glaucoma occurs mainly as a result of certain medicines, far-sightedness or an abnormality in the drainage angle of the eye.  It can even occur naturally when the eye dilates in low light. Angle-closure glaucoma can lead to a medical emergency if it is left untreated and fluid is unable to drain from the eye.

There are many different sub-types of glaucoma.

Normal-tension glaucoma (also NTG, low tension glaucoma, normal pressure glaucoma) is a condition where the optic nerve is damaged although intraocular pressure (IOP) is within normal range.  This can occur as a result of reduced blood-flow to the optic nerve, cell death in nerve-cells and metabolic damage to the optic nerve.

Pseudoexfoliative glaucoma occurs as a result of an accumulation of microscopic granular protein fibers, which can block the normal drainage of fluid from the eye.

Pigmentary glaucoma occurs when pigment is dislodged from the iris and clogs the drainage structures.

Angle recession glaucoma occurs when scar tissue from blunt trauma obstructs the outflow of fluid.

Congenital glaucoma is often inherited and arises from the abnormal development of the eye’s drainage angle before birth.

Neovascular glaucoma is caused by various disorders that cause blood vessels to proliferate on the iris and in the eye’s drainage structures.


Although glaucoma is most common in adults over the age of 40, the risk is not determined by age alone. Studies have shown individuals at greater risk for glaucoma may fit one or more of the following criteria:

  • over the age of 60
  • a family history of glaucoma
  • African descent
  • diabetes
  • history of corticosteroid use

It is thus important for individuals in the general population to have regular eye screening at least every two years after the age of 40.


Glaucoma treatment aims to decrease intraocular pressure by controlling fluid production and drainage from the eye and thus preventing damage to the optic nerve. Initial therapy will generally include the prescription of single eye drops or an eye drop containing a combination of medicines.  This is the mainstay of glaucoma therapy.  In severe cases surgery may be recommended.

(Disclaimer: The purpose of this article is to provide general information and not to substitute any medical diagnosis or advice received from a qualified healthcare professional.)

The Merck Manual. Overview of Glaucoma. [Online]

Available at: (Last accessed 14 June 2016).