INSIGHT INTO GLAUCOMA

by Moorfields Eye Hospital

Glaucoma is a leading cause of blindness. In most cases there are no warning signs. Having regular eye checks will help detect the onset of the disease. Blindness is preventable if glaucoma is diagnosed and treated early enough in the course of the disease.

What is glaucoma?

It is an eye condition characterised by loss of vision due to damage of the optic nerve. The optic nerve carries sight images to the brain, any damage to the nerve results in damage to sight. Usually, but not always, glaucoma is accompanied by an increase in intra-ocular pressure (IOP) (pressure within the eye). It is the pressure that damages the nerve.

Are there different types of glaucoma?

Yes.
Chronic (primary open angle) glaucoma - this form usually affects both eyes and develops slowly so that loss of sight is gradual. There is no pain, redness of the eye or dramatic change in vision.

Acute (angle closure) glaucoma - there is a sudden increase in the intraocular pressure of one eye. The eye becomes red and painful. Often there is mistiness of vision and episodes of seeing haloes around lights.

Secondary glaucoma - in this group of conditions an increase in the intraocular pressure is caused by other diseases of the eye.

Congenital glaucoma (buphthalmos) - is a condition where glaucoma is present from birth. An increase in intraocular pressure causes the eye to enlarge.

The rest of these pages will concentrate only on chronic open angle glaucoma.

What causes the pressure to rise?

The contents of the eyeball are nourished by a fluid (aqueous humour). This fluid is NOT the same as tears. Aqueous is secreted by a tissue within the eye called the ciliary body It circulates around the structures within the eyeball and leaves the eye via the trabecular meshwork sited in the anterior chamber at the front of the eye.

An increase in intraocular pressure in chronic open angle glaucoma occurs when there is progressive obstruction within the trabecular meshwork. It is this persistent increase in intraocular pressure which may damage the optic nerve and cause sight to be lost. This eye pressure is not the same as blood pressure.

Hospital Tests
How is the intra-ocular pressure measured?

An anaesthetic drop will be given to numb the front of the eye. At the slit lamp, the doctor or nurse will shine a blue light into your eye. The surface of the cornea (window of the eye) will lightly be touched with an instrument which measures the pressure.

Will I need any other tests?

Yes, one or more of the following:

Gonioscopy - An anaesthetic drop is given to numb the front of the eye. The ophthalmologist holds a special lens against the cornea. This allows a view of the angle between the iris and the cornea and allows examination of the trabecular meshwork.

Fields - The visual field is the range of sight we have on each side of an object on which we look. The extent of this visual field can be measured. The visual field test takes about 15 minutes per eye and is painless. You will be asked to sit at a screen and keep your gaze fixed on a central light source. You will need to indicate (by pressing a button) if you can see a series of other lights, no matter how dim, shone during the test. You are not expected to see all the lights. This test detects if there are any areas of your visual field where a defect has occurred (missing areas) caused by damage to the optic nerve.

Optic nerve assessment - Dilating drops will be put in your eyes to make your pupils bigger. The effect of these will wear off after a few hours but may temporarily blur your vision preventing you from reading or driving. You are advised not to drive to clinic appointments. The doctor will then examine the inside of the back of the eye using an ophthalmoscope at clinic appointments. This allows the doctor to chart the health of the optic nerve (optic disc).

Photographs - Colour photos taken of the back of the eye are kept in your file and can be used to establish whether any changes occur later. Before photography dilating drops (as above) are given.

Treatment
Can glaucoma be treated?

Yes but not cured. The aim of treatment is to lower the intra-ocular pressure to safe limits and so prevent further visual loss. The first form of treatment is usually eyedrops. The use of eyedrops is the most important part of your treatment of glaucoma. Treatment can only control not cure the condition and must be continued throughout life.

Why are the drops so important?

The drops are a fluid form of medicine for the eye. Putting drops in properly and as prescribed is essential to try to prevent any further sight loss. Please ask for further information. Drops may sting when first used. One eye drop, Pilocarpine, makes your pupil smaller and can temporarily cause brow ache each time the drops are used. In dim lighting your vision may appear worse. These effects usually wear off after 1 or 2 weeks.

Will I notice any effects in myself from the drops?

Side effects may arise from the drop being absorbed quickly into the blood stream. You can slow the absorption by pressing your forefinger of your free hand against the lower lid where it meets your nose; or close your eye for 60 seconds. If you notice breathlessness with any eyedrops, stop the drops immediately and consult your General Practitioner. Please inform the clinic doctor if you have a heart or chest condition. Some drops are not suitable for asthmatics.

Will I need any tablets?

Tablets of acetazolamide (Diamox®) or dichlorphenamide (Daranide®) may be given to reduce the amount of aqueous produced. They initially increase the amount of urine passed and salts leaving the body. This can cause some patients to experience tingling in their hands/feet and or nausea and tiredness. If you notice any side effects tell your ophthalmologist.

Will an operation help?

In some forms of glaucoma an operation may be necessary. The most common operation is: Trabeculectomy - in this operation a small piece of tissue is removed to make a new opening for the aqueous fluid to escape. The escaping fluid is absorbed from the tissues which form the outer coat of the eye

General Questions
How did I get glaucoma?

Glaucoma is not catching, and is not caused by dietary, work or other factors. Some groups of people are known to be more at risk. They are:
Blood relatives of someone diagnosed with glaucoma particularly brothers and sisters.
Afro-Caribbean peoples.
People with severe myopia (shortsightedness).

Is there any way to prevent it?

No, but having regular eye checks will enable early detection and treatment. Everyone should have regular eye checks but especially those in the above categories. Sight tests are FREE for diabetics and certain blood relatives of those with glaucoma. Current legislation provides for parents, offspring, brothers, and sisters of the person affected.

Will I go completely blind?

This rarely happens. Providing you receive treatment, use drops and drugs as prescribed and re-attend for checks that the treatment is working, sight loss should be minimised.

What other help is available?

For those patients who have lost vision associated with their glaucoma and find this distressing, counselling is available. If you wish to talk to someone then please ask your clinic doctor who will refer you appropriately. The social workers in Moorfields social work department 020-7253 3411 are available to provide counselling, and advice about training, employment, aids to daily living or any other issues you may wish to discuss. Registration as partially sighted or blind is not compulsory but provides access to specialist workers, some social security benefits and other benefits which might improve your quality of life.

Can I continue to drive?

The law requires you to inform the Licensing Authority (and insurance company) of any change in health or sight likely to affect the safety of your driving such as being told you have glaucoma in both eyes. You must be able to read a numberplate at 20.5 metres (25 yards) in good daylight and with spectacles if worn. You must also have an adequate field of vision. The Licensing Authority may request a report from your ophthalmologist. Standards are more stringent for vocational drivers. To drive when you are unable to meet the standard is an offence and may invalidate your insurance. Inability to meet these standards requires you to notify the Licensing Authority. You should NOT drive until you have had confirmation that your vision meets the standards.

Other useful addresses are:
International Glaucoma Association
PO Box 75
London
SE5 9RU

Royal National Institute for the Blind
224 Great Portland Street
London
W1N 6AA

These pages are intended only to provide general information for patients. Any patient who is worried or unsure about his or her individual circumstances should seek specialist advice relating to his or her individual circumstances.