Glaucoma

Glaucoma is the name given to a group of conditions that cause vision to become impaired. One or both eyes can be affected by glaucoma, though it is most common for both eyes to be affected, and in many cases one eye tends to be worse than the other. Glaucoma can be very serious and even lead to blindness if left untreated. It develops as a result of tubes in the eye becoming blocked, which prevents fluid from draining from the eye properly. This build-up of fluid causes strain within the eye to increase and this can cause harm to the optic nerve, which sends signals from the retina at the rear of the eye to the brain.

There are different types of glaucoma: chronic open-angle is the most common type, affecting around 1 in 50 people over the age of 40 and 1 in 10 people over the age of 75 in the UK. Glaucoma tends to more common in people with African-Caribbean or Black African heritage.

Types of glaucoma

There are four main types of glaucoma, which include:

Chronic open-angle glaucoma: this is the most common form and tends to develop gradually.
Primary angle-closure glaucoma: this is a rare form which can come on suddenly or progress slowly. It can cause severe pain as a result of a sudden build-up of strain inside the eye.
Secondary glaucoma: this type of glaucoma occurs as a result of other eye conditions (usually uveitis) or injury to the eye.
Developmental glaucoma: this is a rare form which can be very serious and tends to develop at birth or soon after.

What causes glaucoma?

Glaucoma occurs as a result of the drainage tubes in the eye becoming blocked, which prevents fluid called aqueous humour from draining away. The fluid collects and this increases the strain inside the eye, which is known as intraocular pressure. In a healthy eye fluid is constantly flowing in and out of the eye and the pressure generated by the fluid gives the eye its shape. However, if the fluid cannot drain away this increases the strain, which can in turn cause damage to the optic nerve. It is not fully understood why the drainage tubes become blocked and why only some people develop glaucoma. However, some risk factors have been identified (these are factors which increase the danger of developing a condition, which does not necessarily mean an individual will develop the condition):

Age: glaucoma tends to affect older people and it is most common in those over the age of 75.
Ethnicity: glaucoma is most common in people of African or Afro-Caribbean descent, and people of Asian heritage have a higher risk of developing acute angle-closure glaucoma.
Being short-sighted (myopic).
Ocular hypertension: this is a condition that causes increased pressure in the eye.
Family history.
Underlying health conditions, including diabetes.
Other eye conditions, including uveitis, can increase the risk of glaucoma.

What are symptoms of glaucoma?

Symptoms of glaucoma may vary according to the type:

Chronic open-angle glaucoma: this condition usually develops slowly and you may not experience any symptoms. Many of those with this form of glaucoma do not even realise that they have the condition. Peripheral vision tends to be affected first and this gradually spreads to central vision. It is important to attend regular eye tests, especially if you are over the age of 60, so that any symptoms can be detected early.

Acute angle-closure glaucoma: this form of glaucoma develops quickly and symptoms include:

Severe pain.
Headache.
Tenderness around the eye.
Redness.
Sudden loss of vision in one or both eyes.
Sickness.

Symptoms tend to come and go but with each episode the eye is suffering damage, so you should see your GP as soon as possible if you experience these symptoms. If you cannot get an appointment or it is out of hours, visit your local accident and emergency department.

Secondary glaucoma: secondary glaucoma is caused by other eye conditions and the symptoms of glaucoma are easily confused with other illnesses. Glaucoma can cause halos and rings of light around objects and blurred vision.

Developmental glaucoma: it can be hard to detect symptoms of glaucoma in very young children, but the child may exhibit some of the following signs:

Large eyes.
Increased sensitivity to light (known as photophobia).
Watery eyes.
The eyes look clouded.
Sudden eye movements.
A squint.

Complications of glaucoma

If glaucoma is left untreated it can cause loss of sight, which is why regular eye tests are important. Glaucoma causes around 10 percent of cases of blindness in the UK. If you drive glaucoma may affect your ability to do so and you may eventually have to give up as your sight becomes worse. It is important that you notify the DVLA about any conditions that affect your sight.

If you have surgery to treat glaucoma this will carry risks. The most common complication of surgery is an infection, but these can usually be treated quickly and effectively with antibiotics.

How is glaucoma diagnosed?

As symptoms tend to develop gradually, it can take a while to diagnose glaucoma. As the risk of glaucoma is high among older people, it is especially important for people aged over 60 to have regular eye tests (ideally every 12 months), with eye tests being available free of charge on the NHS for over 60s.

During a test of your eyes the optometrist will inspect your eyes, check for signs or symptoms of any problems or conditions and check your sight. There are various tests that can be used to diagnose glaucoma, which include:

Tonometry: this test uses an instrument called a tonometer to measure the pressure inside the eye. Local anaesthetic and dye are placed on the cornea and a blue light from the tonometer is placed against the eye. This test can also be used to diagnose ocular hypertension and is likely to be carried out alongside a central corneal thickness test.
Gonioscopy: this test examines the area at the front of the eye between the cornea and the iris. The gonioscopy test detects whether the angle is closed, which means the tubes are blocked.
Optic nerve test: the optic nerve is a very important nerve which carries messages from the eye to the brain. To examine the optic nerve your optometrist will insert eye drops to make your pupils dilate (become larger). They will then examine your eyes using a slit lamp and check for signs of damage to the optic nerve.

If your optometrist thinks you may have glaucoma they will refer you to an eye specialist, known as an ophthalmologist.

Treating glaucoma

It is not possible to restore vision once you have lost it as a result of glaucoma, which is why it is important to have the condition diagnosed and treated as early as possible. The main aim of treatment is to prevent any further damage to the eye by reducing pressure inside the eye.

Eye drops

The most common treatment for chronic open-angle glaucoma is eye drops. There are different eye drops available and the type you are given will depend on the severity of your condition, and whether you are taking any other medications or have another health problem. The most common types of eye drops include:

Prostaglandin analogue: these drops increase the speed of fluid flowing inside the eye, which reduces pressure.
Beta-blockers: these drops help to reduce pressure by slowing down the production of aqueous fluid.
Carbonic anhydrase inhibitors: these drops work by reducing the amount of fluid produced in the eye.

If eye drops are not effective other treatments may be recommended, including:

Laser treatment

Laser treatment is designed to open up the drainage tubes that are blocked, which helps to restore the flow of fluid in the eye and reduce pressure. This procedure is called laser trabeculoplasty. Local anaesthetic will be placed in the eye before a laser beam is shone through a special lens, which is positioned in front of your eye. The laser beam will cause small holes to develop in the tubes allowing fluid to drain.

Another type of laser procedure, called cyclodiode laser treatment, is also available. This procedure involves blasting some of the tissue that makes the aqueous fluid, reducing the amount of fluid in the eye and subsequently reducing pressure.

Laser treatment tends to be safe, quick and simple, but you may still need to use drops for a short while after the procedure.

Surgery

The most common type of surgical procedure is a trabeculectomy, which involves removing part of the network of drainage tubes to allow fluid to flow freely through the eye. This procedure is usually carried out under local anaesthetic. Other surgical procedures include:

A viscocanalostomy: this procedure involves removing part of the front covering of the eye, called the sclera.
A deep sclerectomy: this procedure involves implanting a very small device into the eye to increase the width of the drainage tube network.
Aqueous shunt implant: this procedure involves placing a shunt into the eye to facilitate the drainage of fluid from the eye.

Acute angle-closure glaucoma develops very quickly and treatment must be given as soon as possible. The main treatments include:

Eye drops.
Systemic medication: this is given intravenously.
Laser treatment: a procedure called laser iridotomy can be used to create tiny holes in the iris, which allows fluid to drain from the eye. Both eyes will always be treated with this treatment.

Preventing glaucoma

It is not possible to prevent glaucoma, but attending regular eye tests will ensure that the condition is detected and treated early. Free sight tests are available on the NHS for people over the age of 60 and for those over the age of 40 with a close relative with glaucoma.