Types of glaucoma
There are four main types of glaucoma:
- chronic open-angle glaucoma – this is the most common type of glaucoma and develops very slowly
- primary angle-closure glaucoma – this is rare and can occur slowly (chronic) or may develop rapidly (acute) with a sudden, painful build-up of pressure in the eye
- secondary glaucoma – this mainly occurs as a result of an eye injury or another eye condition, such as uveitis (inflammation of the middle layer of the eye)
- developmental glaucoma (congenital glaucoma) – a rare but sometimes serious type of glaucoma which occurs in very young children, caused by an abnormality of the eye
Glaucoma can be treated with eye drops, laser treatment or surgery. But early diagnosis is important because any damage to the eyes cannot be reversed. Treatment aims to control the condition and minimise future damage. If left untreated, glaucoma can cause visual impairment. But if it’s diagnosed and treated early enough, further damage to vision can be prevented.
Attending regular optician appointments will help to ensure any signs of glaucoma can be detected early and allow treatment to begin.
How common is glaucoma?
Chronic open-angle glaucoma affects up to two in every 100 people over 40 years old and around five in every 100 people over 80 years old. Some types of glaucoma, such as acute angle-closure glaucoma, are much less common.
Symptoms of glaucoma
Symptoms of the different types of glaucoma are explained below.
There are four main types of glaucoma:
- chronic open-angle glaucoma – the most common type which often has few symptoms
- acute angle-closure glaucoma – which often has severe symptoms
- secondary glaucoma – caused by other conditions or eye treatments
- developmental glaucoma – a rare condition affecting young babies
Chronic open-angle glaucoma
In cases of chronic glaucoma, there are usually no noticeable symptoms because the condition develops very slowly. People don’t often realise their sight is being damaged because the first part of the eye to be affected is the outer field of vision (peripheral vision). Vision is lost from the outer rim of the eye, slowly working inwards towards the centre.
Changes in vision are often linked to getting older, which is why it is so important to have your eyes checked regularly. You should have an eye test at least every two years.
Acute angle-closure glaucoma
Acute angle-closure glaucoma develops rapidly. Symptoms are often severe. They include:
- intense pain
- redness of the eye
- tender eye area
- seeing halos or ‘rainbow-like’ rings around lights
- misty vision
- loss of vision in one or both eyes that progresses very quickly
As a result of these symptoms, some people may also feel sick or be sick. Symptoms of acute glaucoma are not constant. They can last for one or two hours before disappearing again. But each time the symptoms occur, your vision is damaged a little more. It’s important to seek medical attention if you have any of the above symptoms.
Secondary glaucoma is caused by other conditions, such as uveitis(inflammation of the middle layer of the eye). It can also be caused by eye injuries and certain treatments, such as medication or operations.
It’s possible for the symptoms of glaucoma to be confused with the symptoms of the other condition. For example, uveitis often causes painful eyes and headaches.
However, the glaucoma may still cause misty vision and rings or halos around lights.
Recognising the symptoms of developmental glaucoma (also known as congenital glaucoma) can be difficult due to the young age of the baby or child.
However, your child may display symptoms, such as:
- large eyes due to the pressure in the eyes causing them to expand
- being sensitive to light (photophobia)
- having a cloudy appearance to their eyes
- having watery eyes
- jerky movements of the eyes
- having a squint, which is an eye condition that causes one of the eyes to turn inwards, outwards or upwards, while the other eye looks forward
Causes of glaucoma
Glaucoma is caused by a blockage in part of the eye. This prevents fluid draining out of the eye and increases pressure in the eye, called intraocular pressure.
How the eye works
The eyeball is filled with a watery substance called aqueous humour, which creates pressure in the eye to give it shape. In healthy eyes, this fluid constantly flows in and out of the eye. It drains back into the bloodstream at the same rate that it’s produced to maintain the correct pressure.
Glaucoma occurs when the drainage tubes (trabecular meshwork) within the eye become slightly blocked, preventing the aqueous humour from draining properly. An obstruction within the eye, such as a blood vessel blocking the trabecular meshwork, can also prevent fluid from draining properly.
When the fluid cannot drain properly, the pressure in the eye builds up and can damage the optic nerve (the nerve that connects the eye to the brain) and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).
It’s often unclear why the drainage tubes become blocked or why other parts of the eye obstruct the tubes.
There are a number of things that can increase your risk of developing glaucoma:
- Age (glaucoma becomes more likely as you get older
- Short sightedness (myopia) – people who are short-sighted are more likely to develop chronic open-angle glaucoma
- Ocular hypertension (OHT – raised pressure in the eye) – your eye specialist will be able to diagnose OHT which increases your risk of developing chronic open-angle glaucoma
- Family history – if you have a close relative, such as a parent, brother or sister who has glaucoma, you are at increased risk of developing the condition yourself
- Medical history – people with diabetes may be at increased risk of developing glaucoma
A relatively common cause of secondary glaucoma is known as pseudoexfoliation glaucoma. This type of glaucoma is caused by the body producing abnormal protein fibres, which can block the flow of fluid out of the eye, leading to glaucoma.
The causes of pseudoexfoliation glaucoma are unclear but most experts think that it is a genetic condition. Pseudoexfoliation glaucoma is treated in the same way as primary glaucoma.
It’s important to have regular eye tests so eye problems, such as glaucoma, can be diagnosed and treated as early as possible. If you have glaucoma, it can take a long time before you realise you have a problem with your eyesight. This is because glaucoma usually damages the outer edge of the eye and works slowly inwards. You may not notice a problem until the glaucoma is near the centre of your eye.
You should have an eye test at least every two years or more frequently if advised by your eye specialist. For example, it may be suggested to you to have more frequent eye tests if you have a close relative with glaucoma, such as a parent, brother or sister.
Tests for glaucoma
There are several glaucoma tests that can be carried out. They are painless and quite quick. The tests should be carried out during the same appointment to ensure results are as accurate as possible.
These tests are explained below:
Eye pressure test (tonometry)
An eye pressure test (tonometry) uses an instrument called a tonometer to measure the pressure inside your eye.
A small amount of anaesthetic (painkilling medication) and dye is placed onto the transparent layer of tissue that covers the front of the eye (your cornea). A blue light from the head of the tonometer is held against your eye to measure the intraocular pressure. Tonometry can diagnose ocular hypertension (OHT – raised pressure in the eye), which is a risk factor for chronic open-angle glaucoma.
Central corneal thickness
The thickness of your cornea will be measured because this is thought to affect how the intraocular pressure is interpreted.
Gonioscopy is an examination of the front outer edge of your eye, between the cornea and the iris (the coloured part of your eye). This is the area where the fluid should drain out of your eye. A gonioscopy can help to determine whether this angle is open or closed (blocked).
Visual field test
A visual field test, sometimes called perimetry, checks for missing areas of vision. You will be shown a sequence of light spots and asked which ones you can see. Some dots will appear in your peripheral vision (around the sides of your eyeball), which is where glaucoma begins. If you can’t see the spots in your peripheral vision, it may indicate the glaucoma has damaged your vision.
Optical Coherence Tomography (OCT)
OCT is an indispensable tool for better eye examination. The OCT gives accurate information about the retina and the macula which are responsible for the delivery of sharp images. With this information your eye doctor can recommend the proper treatment, follow the progress of the disease if any, and assess the effectiveness of the treatment. The test is painless, and quick.
Optic nerve assessment
Your optic nerve connects your eye to your brain. Your specialist will use eye drops to enlarge your pupils. Then he / she will examine your eyes using a slit lamp (a microscope with a very bright light) and assess whether your optic nerve has been damaged by the glaucoma. The eye drops used to widen your pupils could affect your ability to drive. You should make alternative arrangements for getting home after your appointment.
Treatment aims to reduce the pressure in the affected eye, called intraocular pressure. Any damage to your vision caused by glaucoma can’t be repaired so it’s important to get an early diagnosis and treatment to prevent further damage.
Chronic open-angle glaucoma is often treated using eye drops. There are several different types of eye drops available, the type prescribed may depend on:
- how your condition is progressing
- whether you have other medical conditions
- whether you are taking any other medications
- whether the eye drops cause side effects when you use them
Laser iridotomy uses a very focused beam of light to create a hole on the outer edge, or rim, of the iris, the coloured part of the eye. This opening allows fluid (aqueous humor) to flow between the anterior chamber, the front part of the eye, and the area behind the iris, the posterior chamber. This opening may decrease pressure in the eye and usually prevents sudden build -up of pressure within the eye, which occurs during an episode of acute closed-angle glaucoma. Some people feel a mild but sharp sensation in the eye during this procedure. But there usually is no pain after laser iridotomy.
A trabeculectomy is the most common type of glaucoma surgery. It involves removing part of the trabecular meshwork to allow fluid to flow through the eye’s drainage system. The procedure will be carried out under local anaesthetic (you are awake) or general anaesthetic (you are unconscious).
Other types of surgery include:
- a viscocanalostomy – this operation removes part of the sclera (the white outer covering of the eyeball), enabling the fluid to filter out of your eye and into your body
- a deep sclerectomy operation – this operation involves implanting a tiny device inside your eye to widen the trabecular meshwork
- an aqueous shunt implant – this operation involves placing a tube device into your eye to increase the drainage of fluid out of your eye
Acute angle-closure glaucoma
As acute glaucoma develops rapidly, the condition needs to be treated quickly. The most common forms of treatment for this type of glaucoma include:
- eye drops
- systemic medicines – these are injected into your bloodstream to quickly reduce the pressure in your eye
- laser treatment
If you also have a cataract (a cloudy patch in the lens of your eye), removing it may open the angle in your eye and control the intraocular pressure.
Monitoring your condition
If you have been diagnosed with glaucoma your condition will be closely monitored to check for further damage to your vision. Depending on how your glaucoma is progressing, you may need further appointments every one to four months or up to 12-24 months apart.
Complications with glaucoma
The main complication of glaucoma is loss of vision that can’t be repaired. This is why early diagnosis and treatment is so important.
Complications from treatment
If you have surgery to treat glaucoma, there is always a risk of infection. Most infections can be treated with a course of antibiotics. You may also have a reaction to certain types of eye drops.