Glaucoma usually develops when the fluid (called the aqueous humour) that fills the front part of your eye can’t drain away properly, increasing pressure inside the eye. However, it's also possible to develop glaucoma with normal pressure in the eye due to a weakness of the optic nerve and in most cases, glaucoma is caused by a mixture of both.
The eye needs pressure to keep the eyeball in shape but if the pressure gets too high, it squeezes the optic nerve which leads to vision loss. The most common type of glaucoma, primary open angle glaucoma (POAG), develops gradually over time, with eye pressure rising slowly. Acute angle closure glaucoma is less common, but happens when the pressure in your eye rises rapidly immediately damaging the optic nerve.
The causes for both types are unclear, but possible causes include a build-up of deposits in the drainage tubes, inflammation inside the eye (uveitis), long-term steroid eye drop use, an eye injury and a problem with the way the eye develops as a child, also known as congenital glaucoma.
The symptoms of glaucoma vary, depending on the underlying cause. POAG may have no symptoms until there’s irreversible loss of vision. As pressure builds up, the peripheral side vision deteriorates but you might not notice this and its usually picked up in an eye test. Eventually it’s like looking through a long tube, referred to as ‘tunnel vision’, which can lead to blindness if not treated.
With acute glaucoma, symptoms include intense eye pain, loss of vision, headache, blurred vision, seeing halos or rainbow like rings, feeling and being sick, red eyes and a tenderness around the eyes. You should seek medical help immediately if this happens.
Glaucoma is usually detected during a routine eye test, which is recommended every two years (more frequently if you are in an at risk group) and there are a number of tests your optometrist may use.
Your optic nerve may be assessed by dilating your pupils and shining a bright light with a slit lamp or ophthalmoscope at the back of your eye. The pressure inside the eye can also be measured by using an instrument called a tonometer, which puffs air into each eye to record the pressure. Your visual field can also be tested by identifying a sequence of spots of light on a screen. If your optometrist suspects glaucoma, they may advise a gonioscopy, which examines the areas of the eye where the fluid drains out.
If you’re over 60 or aged over 40 with a family history of glaucoma or in other high risk groups you’re entitled to a free NHS eye test. If glaucoma is picked up during an eye test, you should be referred to a hospital eye specialist for further tests.
Who gets glaucoma?
You’re at higher risk of glaucoma if you have a family history of the condition, you’re over 40 and if you’re of African, Caribbean or Asian origin and have diabetes.
Treatment will depend on what type of glaucoma you have. Nothing can reverse the damage that glaucoma has done, but it can stop your vision from getting worse.
Eye drops will usually be recommended to lower eye pressure for POAG, and they include prostaglandin analogues, which help the eyes fluid drain out more quickly, beta blockers, adrenaline-type drops and carbonic anhydrase inhibitors. All of these eye drop treatments reduce the amount of fluid secreted into the eye and sympathomimetics, which reduce pressure and reduce the fluid build-up.
There are a range of different treatments, the most common being a trabeculectomy, which may be used as an alternative to laser treatment to improve the drainage of fluids from your eye. This surgery creates a small hole in the eye wall to allow fluid to drain away.
Laser treatment helps improve the drainage of fluids from your eye. The types of laser used include laser trabeculoplasty, which is mostly used in chronic glaucoma, and laser iridotomy, which is more commonly used in acute glaucoma.