Glaucoma is a complex group of eye problems but it can broadly be divided into chronic (or open angle) glaucoma, and acute (also known as closed angle) glaucoma. Chronic open angle glaucoma is the commonest form. Acute glaucoma is much less common but still affects about 1 in 1000 people.
In a normal eye, aqueous fluid circulates through the pupil into the chamber behind the cornea, and drains from this chamber out of the eye through a meshwork of fine vessels located at the outer edge of the iris (the coloured part of the eye).
In some people the route to the meshwork of drainage channels is particularly narrow and in fact is susceptible to closure. When closure occurs, the pressure of fluid inside the eye rises dramatically, usually over a period of several hours, causing intense pain and loss of vision. Provided prompt action is taken to reduce the pressure then normal vision is usually fully restored, but an operation is usually required not only on the affected eye, but usually on the other eye to prevent the same thing occurring in this eye in the future.
Who is at risk?
Acute glaucoma is not very common but usually occurs in people aged 55 or over, and typically even more elderly. People who are quite long sighted (their glasses are thick in the middle of the lens and thinner at the edge) also have an increased risk. There will often be a family history of acute glaucoma too.
Your optometrist can offer advice about the risks of developing acute glaucoma and sometimes it may be appropriate to carry out a further investigation called gonioscopy to help assess the risk. This allows a view of the drainage structures not visible by other means, by placing a special contact lens on the front of the eye. In addition to this, we now have a OCT scanner which can image the drainage structures in great detail. We would strongly recommend both of these procedures to patients who might be at risk of angle closure. These procedures are not available through the NHS General Ophthalmic Services and therefore a charge will be made.
What are the symptoms?
Usually there aren’t any before the drainage system closes. An attack of acute glaucoma can occur very suddenly without any prior warning. When it happens, the eye becomes very painful, with a lot of pain on the forehead and around the eye. The eye itself becomes very red, especially on the white of the eye around the edge of the iris. The cornea becomes hazy and the pupil becomes dilated and is vertically oval in shape. The vision becomes very blurred and hazy, often to the point where it can only see light and dark, or movement. Often the pain is so intense it will induce vomiting.
This is an emergency and requires immediate admission to the nearest hospital with an ophthalmology department (in this area this is the RVI in Newcastle, who operate an eye casualty service during office hours, otherwise A&E at Wansbeck or Newcastle RVI).
A number of people experience sub-acute attacks of angle closure glaucoma before going on to develop complete closure. During these episodes the drainage angles become narrowed but not quite closed, causing a significant rise in pressure within the eye, but then the angle re-opens allowing the pressure to drop again. When these sub-acute attacks occur, most people suffer from a mild ache over their forehead, or around the eye, and usually see quite distinct grey or rainbow coloured haloes around lights. These usually occur in the evening and may be precipitated by drinking fluids (not necessarily alcohol!).
If you think you have experienced these symptoms you must discuss them with your optometrist or your doctor, as you may be at risk of angle closure glaucoma.
People who have experienced sub-acute attacks or who are otherwise judged to be at risk of angle closure may be offered prophylactic (preventative) treatment called a laser iridotomy where a tiny hole is punched through the peripheral iris with a laser. This relieves the pressure and usually prevents an acute attack occurring in the future.
Where someone has an acute attack, as mentioned above it is essential for treatment to start as soon as possible. In this case the pressure inside the eye is reduced initially using drugs, administered usually in a combination of oral, intra-venous or by eye drops. Once the pressure has been stabilised then surgery will be performed on both eyes to permanently lower the pressure.
If treatment is not commenced quickly then the high pressure inside the eye will permanently damage the optic nerve producing irreversible damage to the eyesight.
Useful telephone numbers:
Eye Casualty (RVI switchboard ask for Eye Casualty): 0191 2336161 NHS Direct: 0845 4647 or www.nhsdirect.nhs.uk