Chronic Open-angle Glaucoma

Chronic open-angle glaucoma is a condition which causes damage to the optic nerve at the back of your eye and which can affect your vision. It is usually caused by an increase in pressure within your eye. If it is not treated, glaucoma can lead to visual loss and even to total loss of vision (severe sight impairment.) Treatment can slow down glaucoma and help to prevent this. All adults aged over 35-40 should have a regular eye check which includes measurement of their eye pressure.


When you look at an object, light from the object passes first through the cornea of your eye, then the lens and then hits the retina at the back of your eye. The cornea and the lens both help to focus the light on to your retina. Nerve messages pass from the 'seeing cells' (rods and cones) in your retina, down nerve fibres in your optic nerve to your brain. The messages are interpreted by your brain, which enables you to see.

The black area in the middle of the eye (the pupil) helps to regulate the amount of light that gets into the eye. It does this by becoming smaller (constricted) when the light is brighter and larger (dilated) in dark conditions. The muscles of your iris (which gives colour to your eye) control the size of your pupil.

Your eye also needs to keep its shape so that it can work properly and so that light rays are focused accurately on to the retina. So, most of your eye is filled with a clear jelly-like substance called the vitreous humour (humour meaning fluid). The front of your eye is filled with a clear watery fluid called aqueous humour.

The part of your eye behind the lens is called the posterior chamber and is filled with vitreous humour. The part of the eye in front of the lens is called the anterior chamber and is filled with aqueous humour.

Aqueous humour is made continuously by the cells of the ciliary body (which is at the back of the iris at its base). It passes through the pupil from the posterior chamber to the anterior chamber. From there it drains away through a sieve-like area called the trabecular meshwork (which is in front ot the iris, also near its base.) So, there is constant production and drainage of aqueous humour fluid. This keeps the fluid levels balanced.


COAG develops slowly and painlessly, so that any damage to the optic nerve and loss of sight are gradual and you may not notice anything has changed until the condition is very advanced. The term 'open-angle' refers to the angle formed in the eye between the outer edge of the iris and sclera. In COAG this is normal, whereas in acute angle-closure glaucoma (AACG), which is a much less common condition, it is narrowed or blocked off. See separate leaflet called Acute Angle-closure Glaucoma for more details.

The rest of this leaflet deals only with COAG, referred to from this point as glaucoma.

In glaucoma there is a partial blockage within the trabecular meshwork through which the aqueous humour drains. This restricts the drainage and results in a build-up of pressure. The reason why the trabecular meshwork becomes blocked and does not drain well is not always fully understood. The aqueous humour builds up if the drainage is faulty and this increases the pressure within your eye.







  • Have a family history of glaucoma.
  • Have very short sight.
  • Have diabetes.
  • Are of African or Afro-Caribbean origin.
  • Are older.



Because there are usually no symptoms at first screening for glaucoma is very important.

Everyone aged over 35 to 40 should have an eye check by an optician at least every five years. A check every two to three years is advised if you are aged over 50. Eye checks are particularly important if you are in any of the at-risk groups listed above, or if you are found to have raised pressure in your eyes. The eye check will detect early signs of glaucoma before any significant vision loss occurs. Most people with glaucoma have it detected at a routine eye check.



The pressure in your eyes (intraocular pressure) will also be measured.This is commonly done using a 'puff of air' test (tonometry).



Your field of vision will also be tested. This is essentially how much of the world you can see whilst you are looking directly forward. Glaucoma affects the outside (periphery) of your field of vision first.



Eye drops







Laser treatments


Eye drops are sometimes still needed after laser surgery.







Now read about Primary Open-angle Glaucoma

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Original Author:
Dr Tim Kenny
Current Version:
Dr Mary Lowth
Peer Reviewer:
Dr Colin Tidy
Document ID:
4256 (v46)
Last Checked:
25 June 2015
Next Review:
24 June 2018
The Information Standard - certified member



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