Types of glaucoma
What are the different types of glaucoma?
There are four main types of glaucoma: primary open angle glaucoma, primary angle closure glaucoma, secondary glaucoma and developmental glaucoma.
Primary open angle glaucoma (POAG)
This is the most common form of glaucoma. It is a chronic (slowly-developing) condition in which the eye pressure rises because the drainage channels themselves are not good enough at draining fluid out of the eye. This is not because of an obstruction blocking the flow: as the name of this type of glaucoma suggests, the drainage angle remains ‘open’. The eye pressure rises very slowly and there is no pain to warn of a problem, even though the optic nerve is being damaged. Often, one eye ‘fills in’ for the other because the damage is not necessarily occurring in the same part of the field of vision in both eyes. For this reason, much damage will often have been done before the sufferer realises there is a problem with his/her sight. It is important to diagnose and start treating this kind of glaucoma early on, before it has advanced to a stage where there has been extensive sight loss.
Primary angle closure glaucoma (sometimes called ‘acute glaucoma’)
This sort of glaucoma is less common in Western countries and more often found in people of Asian origin. It may be acute (sudden onset) or chronic (slowly developing).
Acute primary angle closure develops when the access of the aqueous humour to the trabecular meshwork is blocked because the iris has come forward, causing the drainage angle to ‘close’. This means that fluid cannot escape from the eye and the pressure rises. This tends to be very painful because the rise in pressure happens suddenly. Symptoms include seeing halosaround light sources, a red eye, cloudy vision and occasionally, sickness. It must be treated straight away and in most cases, the vision recovers completely. However, if treatment is delayed, there is often permanent damage to the eye and sight is irretrievably lost. When damage to the nerve has occurred, the term primary angle closure glaucoma is used. The tendency for this glaucoma to develop depends on the shape of the eye and is more common in ‘long-sighted’ eyes.
Sometimes people experience a series of mild attacks of angle closure. These are called subacute attacks and often occur in the evening. Vision may seem misty, with coloured rings around white lights and there may be some discomfort and redness in the eye and a feeling of sickness. If you have these symptoms, you should consult your doctor without delay.
Chronic angle closure develops slowly, usually without symptoms, although the reason for the rise in eye pressure is similar to acute primary angle closure glaucoma. When damage to the nerve has occurred, the term chronic primary angle closure glaucoma is used. Treatment is given to reduce the level of eye pressure to a level at which no further damage to the optic nerve occurs.
Secondary glaucoma
This kind of glaucoma can either be open angle or closed angle in nature – in other words, there are various ways in which the eye pressure rises. It has an identifiable cause, being ‘secondary’ to another condition. As well as treating the glaucoma, the other condition which has caused the glaucoma must also be addressed. The eye may then return to a normal state and not require further treatment, or it may have been damaged so that ongoing glaucoma treatment will be required.
This is a rare condition where the eye has failed to form properly. It is present in about 1 in 10,000 babies and may be associated with other developmental abnormalities of the eye. For full details of symptoms and treatments, contact the International Glaucoma Association and ask for our booklet ‘Glaucoma in Babies and Children’.
Top
