What is glaucoma?

Glaucoma is a group of eye diseases that damage the optic nerve (a bundle of millions of nerve fibres which transmit electrical signals from the retina at the back of your eye, to the visual cortex in your brain). This damage is usually caused by fluid buildup in the eye, which increases eye pressure.

Glaucoma is the leading cause of sight loss among those of working age, and is often referred to as ‘the sneak thief of sight’ as it can take a long time for symptoms to develop, but any damage done is irreversible. As such, regular eye tests are vital so the condition can be diagnosed and treated quickly, ensuring sight can be preserved. If untreated, vision loss starts at the outside of your visual field and gradually affects your central (detailed) vision.

Types of glaucoma

There are four main types of glaucoma:

Primary open-angle glaucoma

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This is the most common type of glaucoma where the filter that drains fluid from the eye becomes partially blocked. As a result, pressure in the eye gradually increases and slowly damages the optic nerve.

This type of glaucoma is painless and vision loss is so gradual that it may not be noticed until significantly impaired.

Primary angle-closure glaucoma

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The filter that drains fluid from the eye is located between the iris and the cornea. When someone’s iris bulges forward and narrows or blocks the part of the eye where the filter is located, pressure increases in the eye. This can happen quickly (acute angle-closure glaucoma) or gradually (chronic angle-closure glaucoma).

Acute angle-closure glaucoma is a medical emergency.

Secondary glaucoma

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Secondary glaucoma includes any type of glaucoma where eye pressure, and resulting damage to the optic nerve, is caused by another condition. Types of secondary glaucoma include:

  • Uveitic (inflammatory) glaucoma

This type of glaucoma can happen in people who have uveitis.

  • Neovascular glaucoma

Neovascular glaucoma occurs when your eye makes extra blood vessels that cover the filter that drains fluid from the eye, increasing pressure. It is always associated with other conditions, most commonly diabetic retinopathy.

  • Pigmentary glaucoma

Pigmentary glaucoma occurs due to pigment dispersion syndrome (PDS) where pigment (colour) from your iris flakes off and blocks the part of the eye that drains fluid, increasing pressure in the eye.

  • Traumatic glaucoma

Traumatic glaucoma occurs when pressure inside the eye is increased due to an injury to the eye, and can often appear years after the injury took place.

Congenital glaucoma

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Some babies are born with an abnormality in the drainage canal of the eye, which prevents fluid from draining as it should, and increases pressure in the eye. This leads to congenital glaucoma.

This type of glaucoma is painless and vision loss is so gradual that it may not be noticed until significantly impaired.

There is also a type of glaucoma called low-tension or normal tension glaucoma, where your optic nerve is damaged despite your eye pressure being normal. It is not currently known what causes this damage.

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