What is glaucoma?

Glaucoma is an eye disease that can cause blindness; it is one of the main causes of blindness in New Zealand. If caught early, it can usually be controlled. But it often has no symptoms, so you need regular eye exams to check for it.

Glaucoma usually begins when pressure builds up in the aqueous fluid of the eye (this fluid bathes the inside of the eye, unlike tears which bathe the outside). This pressure (intraocular pressure) can damage the optic nerve. The optic nerve sends messages to the brain so that you can see. There are two main kinds of glaucoma: "open-angle" and "closed-angle."

Drainage area
Aqueous fluid is made inside the eye and bathes tissues in the front part of the eye before being drained away through a sieve-like system called the trabecular meshwork. The eye is always producing fluid. The eye's drainage areas may become clogged or blocked. Too much fluid stays in the eye. This increases eye pressure.

Optic nerve
Too much pressure in the eye can damage the optic nerve. If damaged, this nerve cannot send the messages to the brain that let you see.

Types of glaucoma include:

Open-angle glaucoma
Open-angle is the most common kind of glaucoma. It occurs slowly as people age. The drainage area in the eye becomes clogged. Not enough fluid drains from the eye, so pressure slowly builds up. This causes gradual loss of side (peripheral) vision. You may not even notice changes until much of your vision is lost.

Closed-angle glaucoma
Closed-angle glaucoma is less common than open-angle. It usually comes on quickly. The drainage area in the eye suddenly becomes completely blocked. Eye pressure builds rapidly. You may notice blurred vision and rainbow halos around lights. You may also have headaches, nausea, vomiting and severe pain. If not treated right away, blindness can occur.

Secondary glaucoma is associated with underlying ocular conditions: uveitis, retinal blood vessel occlusions and trauma.

Risk factors for glaucoma include:

• elevated pressure within the eye (intraocular pressure)
• positive family history of glaucoma
• increasing age
• associated conditions: high blood pressure, diabetes, myopia (short-sightedness).

The older you are and the more risk factors you have, the more important it is to have regular eye examinations.

How is it diagnosed?

Gradual loss of vision in open-angle glaucoma, usually without other warning symptoms, progresses from the periphery (sides) to the centre of your visual field (eg, the animated image on the right). Most people learn they have glaucoma during an eye exam. Simple tests that measure your eye pressure and magnify the inside of your eye usually alert your eye doctor to a problem. Other tests reveal loss of vision and damage to the delicate structures of the eye.

What can be done?

Your eye doctor cannot restore vision that has already been lost, but in most cases eye pressure can be lowered to prevent further loss of sight. Treatment depends on the type of glaucoma that you have and how it responds to medication. In some cases your eye doctor may suggest laser treatment or surgery.

Treatment

The aim of treatment is to lower intraocular pressure and to stop the progressive loss of vision high pressure causes. Early diagnosis usually results in a more favourable prognosis.

Medicines to lower eye pressure: Eyedrops and pills may be used to lower eye pressure. Some medicines reduce the amount of fluid your eyes make. Others increase drainage in the eyes. Use your medicines as directed. Don't stop taking them - even if you have no symptoms. If you do, eye pressure can rise rapidly and damage your vision. If the medicines cause side effects, talk to your doctor.

Laser treatment: Argon laser treatment (trabeculoplasty) is for primary open-angle glaucoma. The bursts of laser energy at precise points stretch the tissues and open the clogged drainage holes. YAG laser treatment (iridotomy) is for closed-angle glaucoma.

Surgery: Filtering surgery (trabeculectomy) to bypass the existing drainage pathway by making another small hole. Most often used when medical therapy is inadequate, in younger patients and in secondary glaucoma.

Laser treatment and eye surgery are outpatient procedures done with local anaesthetics. You may still need to take pills or eye drops to help control your pressure after laser treatment or surgery.

How long is treatment required?

Once the diagnosis of glaucoma is established, treatment with medication (pills or eyedrops) is lifelong and aims to slow the progression of the disease by keeping the pressure low. Regular follow-up with intraocular pressure recording, optic disc examination and visual field analysis by your eye doctor is therefore very important.

Both eyedrops and pills allow the drug into your bloodstream, so they can cause side effects in a few people such as headaches, eye irritation, blurred or dim vision with eyedrops; or tingling, nausea, loss of appetite, drowsiness, bowel problems with tablets. If you have problems with taking your medication talk to your doctor about it.

For further information and support talk to an optometrist or eye specialist. Optometrists are listed in the "Yellow Pages" of your telephone book. Eye specialists are listed with registered medical practitioners at the front of the white pages of your telephone book.

Original material provided by Auckland Eye and StayWell Krames, and reviewed May 2005. Edited by everybody.