What is glaucoma?

The optic nerve is a bundle of about 1 million individual nerve fibres responsible for sending visual information from your retina to your brain, where electrical impulses are turned into images.

Vision loss in chronic glaucoma typically starts in your peripheral/side vision and is so gradual that it could go unnoticed for a long time without early symptoms as warning signs, making regular eye tests crucial.

Glaucoma can be caused by a buildup of a naturally occurring watery fluid within the eye called the aqueous humour. The function of the aqueous fluid is to keep the eye healthy by providing it with nourishment and maintaining the eyes shape. Usually, the aqueous fluid drains at the same rate as it is produced.

This build-up of the aqueous fluid can create an increase in the pressure within the eye referred to as intraocular pressure or IOP. This raised pressure may damage the optic nerve leading to vision loss if it is left untreated.

Pressure build-up may occur due to limited outflow of aqueous if the structure that drains the fluid out of the eye is damaged due to a narrowing or closing. The structure that drains the fluid is called the trabecular meshwork; a spongy network of holes found in the angle where the cornea (clear front surface of the eye) meets the iris (colour part of the eye).

Another cause for pressure build-up in the eye can be an over production of aqueous fluid.

Glaucoma can also be a cause of a weakness in the optic nerve structure. In this instance glaucoma can be present even if your eye pressure falls within the normal range and is sometimes called ‘low tension’ glaucoma.

The normal range for eye pressure falls between 10 to 21 mmHg (millimetres of mercury). However not everyone with higher than normal eye pressure develops glaucoma.

In a rarer form of glaucoma the IOP can rise suddenly if the drainage angle closes completely, this is called acute angle closure glaucoma. In this instance the pressure can rise rapidly, and the person will notice their vision becomes blurred, they will experience pain in and around their eyes, their eye will be red, they might see coloured halos around lights, and have headache, nausea and vomiting. Acute angle closure glaucoma requires urgent medical care.