The signs of glaucoma
Glaucoma is an eye condition which happens when pressure builds up inside the eyeball. There are two main types. The most common type - often just called glaucoma - is referred to by doctors as chronic glaucoma or chronic open-angle glaucoma. This type of glaucoma comes on slowly and painlessly, which means you may not know you have it until it has already damaged your eyesight. That's why it's so important to get regular checks from your optician, and to know the signs.
What causes glaucoma?
The inside of your eye is filled with a thin, watery fluid called aqueous humour. Made up of more than 99% water, this fluid helps keep the eyeball in shape and nourishes the lens and cornea - the transparent covering of the eye. This clear fluid is constantly being produced and drained away - in a healthy eye, fluid is added and removed at the same rate, keeping the pressure inside the eyeball steady.
Normally aqueous humour drains away through a mesh called the trabecular meshwork. In glaucoma, the mesh gets slightly blocked and the fluid can't drain away at the right rate - rather like a partially blocked plughole or drain. That means fluid comes in faster than it drains away, resulting in a build-up of pressure inside the eyeball.
What is usually the first sign of glaucoma?
Because the symptoms of chronic glaucoma tend to come on gradually, your eyesight may be permanently damaged before you notice any symptoms.
Untreated glaucoma is one of the world's leading causes of severe loss of eyesight. It's crucial to have regular eye checks with an optician, who can pick up early signs of raised pressure inside your eyes, at least every two years if you're over 35 years old.
How is glaucoma diagnosed?
Your optician will measure the pressure inside your eyes with a simple, painless test involving blowing a puff of air at the front of your eye. They will also measure your vision, including your peripheral vision. In addition, they will check the retina and the optic disc, where nerves from the retina come together and form the optic nerve, which communicates with the brain.
If glaucoma runs in your family, you should be tested more often.
If you do have a family history of glaucoma, you're entitled to a free NHS eye check every year once you reach age 40.
What is the difference between chronic glaucoma and acute glaucoma?
The trabecular meshwork, which drains aqueous humour, is found at the angle between the iris (the coloured ring in your eye with the pupil in the middle) and the cornea (the transparent layer at the front of the eye, covering your iris).
If this angle is partly open, it has the medical name chronic open-angle glaucoma, or chronic glaucoma. Aqueous humour still drains out of the eye, but not as fast as it should. This means the pressure inside the eye is high, but it tends to build up slowly and there's not a complete blockage. Symptoms come on slowly and there's no pain. However, it can still damage your eyesight in the longer term if it's not treated.
Sometimes the angle can get completely blocked, with the iris squashed against the cornea. This completely blocks the trabecular meshwork, as well as another drainage channel called the uveoscleral outflow. Aqueous humour can't get out at all, leading to very rapid increase in pressure inside the eye. This is known as acute closed-angle glaucoma, which can cause blindness very quickly if not treated.
What are the symptoms of chronic glaucoma?
The back lining of your eye - the retina - is covered with a thin layer of 'seeing cells'. These are activated by light falling on them and transmit messages to your brain through tiny nerve endings, which come together to form a nerve at the back of your eye, called the optic nerve.
If the pressure inside your eyeball builds up, it can press on the delicate nerve endings and damage them.
Over time, this can lead to loss of eyesight in patches or, eventually, severe loss of vision. Glaucoma becomes more common with age, and you're at higher risk if you have diabetes, are very short-sighted, or if a parent or sibling has glaucoma.
Chronic glaucoma doesn't usually cause symptoms in the short term. This is because the outer part of your vision - peripheral vision - is affected first and one eye often fills in the blanks if the other eye is affected. It usually affects both eyes, but one may be more affected than the other. If it isn't caught, your central vision can gradually become affected.
What is the treatment for chronic glaucoma?
Standard treatment for chronic glaucoma is with laser surgery - done quickly and easily under local anaesthetic. You may also be offered treatment with regular eye drops. These are usually given:
- While you're waiting for surgery.
- Instead of laser surgery if you don't want surgery.
- If you have a medical condition which makes you unsuitable for surgery.
- Following surgery, if the pressure inside your eye remains high.
- In addition to surgery if the pressure is seriously high or you are at high risk of losing your vision.
What causes acute glaucoma?
Like chronic glaucoma, acute glaucoma is the result of raised pressure inside your eye. However, in acute glaucoma, the complete blockage of the flow of aqueous humour out of the eye results in a rapid, steep rise of pressure inside the eye.
Acute glaucoma can be triggered by certain medications, including eye drops used to dilate your pupil - sometimes used for eye checks - some antidepressants or steroids, or medicines used for stomach problems or general anaesthetic.
What are the symptoms of acute glaucoma?
- Sudden severe pain in one eye.
- Circular lights like haloes around bright lights.
- Blurred or reduced vision.
- Red, hard, tender eye.
- Feeling or being sick.
- Feeling generally unwell.
- Severe headache.
What is the treatment for acute glaucoma?
If you have any symptoms of acute glaucoma, you should go straight to a hospital A&E department - if possible, check the hospital has an eye department before you go. Do not cover your eye - this will make your pupil dilate, which can speed up damage.
Initial treatment involves eye drops or injected medicine to lower the pressure.
Once the pressure has reduced, you will need eye surgery:
- Outpatient laser surgery under local anaesthetic to make small holes in your iris.
- Surgery to make a small hole in your iris.
You will usually be advised to have both eyes treated, because having acute glaucoma in one eye increases the risk of the same condition in the other eye. You will also need to have regular long-term follow up and may need to use regular eye drops.
What is normal-pressure glaucoma?
Around one in five people with glaucoma have normal pressure inside the eyeball - this is called normal-pressure glaucoma. It's not quite clear why this happens, but it's possible that the optic nerve of some people are particularly sensitive to even a slight change in pressure.
Normal-pressure glaucoma can damage your eyesight just as chronic glaucoma does.
Your optician can pick up signs of normal-pressure glaucoma at a routine eye check. If they find evidence of it, they will arrange for you to be referred to an eye specialist - they may send a letter to your GP to arrange this referral. The eye specialist will provide treatment and regular long-term follow up.
What's the difference between glaucoma and raised eye pressure?
Some people have raised pressure inside the eye but don't get any damage to the optic nerve. Whenever you have a regular eye test, your optician will check for both the level of pressure inside your eye and any damage caused by it.
Even if your eyesight is normal, you should still be referred to an eye specialist if you have raised pressure inside the eye. You will need to have regular follow-ups to see if you would benefit from treatment to reduce the pressure in your eyes.
How to prevent glaucoma
The key to preventing eye damage from glaucoma is to get regular eye checks from your optician. Picking up symptoms early and having treatment can reduce damage from chronic glaucoma and cut the risk of developing acute glaucoma.
With thanks to 'My Weekly' magazine where this article was originally published.