Glaucoma is a group of conditions in which the optic nerve is damaged in a characteristic way. This is often associated with a raised intraocular pressure. The intraocular pressure is the pressure of the fluid within the eye that keeps the eye inflated into its normal spherical shape. It is the balance between the rate of fluid secretion into the eye to that of the fluid draining from the eye that determines the pressure inside the eye, the intra-ocular pressure.
The optic nerve damage causes a reduction in the sensitivity that varies in severity from patient to patient. It usually does not affect the central vision. There is not usually any pain or discomfort with chronic glaucoma. Also because the reduction in vision is usually slow and "patchy" and the visual field loss between the eyes is not usually symmetrical, it often goes undetected until an eye examination at your optometrist shows its presence.
Without treatment, the loss of vision usually gets worse over the course of many months or several years. The loss of vision in glaucoma is permanent, but with early treatment, the damage to vision can be minimised.
Most patients with glaucoma are not aware of problems with their vision. This is because the central vision (for reading and recognising people) is only affected when glaucoma has advanced to a late stage.
Even when central vision is still good, glaucoma may affect the vision needed for driving and getting about (for instance, seeing steps). Blindness from glaucoma is rare. If blindness does occur, it is usually because the glaucoma is already advanced when it is first diagnosed, because the eye pressure has not responded well to treatment or because patients have not taken their drops regularly.
For most glaucoma patients, the main effect of the condition is the inconvenience of taking eye drops.
What are the different types of glaucoma?
Adult glaucoma falls into two categories – open angle glaucoma and closed angle glaucoma.
There are various types of glaucoma but primary open angle glaucoma (POAG), also known as chronic glaucoma, is the most common. It has no symptoms in the early stages, but slowly and painlessly destroys sight if it is not detected and treated. The loss of vision cannot be reversed. It mainly affects middle aged and elderly people, although it can develop in younger people. The earlier glaucoma is detected, the more successful the treatment.
Even if you seem to have excellent sight, this doesn't rule out glaucoma because:
Glaucoma initially destroys the off centre vision, leaving the central detailed vision unaffected until a later stage.Blank patches in the field of vision may go unnoticed as the less affected eye 'completes the picture'.Glaucoma does not affect the ability of the eye to focus and the condition may be present even though vision seems fine without the need for glasses.
You could lose a considerable amount of sight irretrievably before you are aware of a problem.
What are the glaucoma tests?
The only way you can know for certain whether or not you have glaucoma is to arrange to have a sight test which includes all three glaucoma tests. These tests are rapid and painless. They are: ophthalmoscopy, tonometry and visual field testing.
A combination of all three tests has been shown to increase the likelihood of detecting chronic glaucoma by four times when compared with ophthalmoscopy alone1. If your optician is not able to perform all three tests, then find one who is. However, the optometrist can make an additional charge for carrying out tonometry and perimetry even if the rest of the test is paid for by the NHS, so it is always worth checking this when arranging a test.
Be aware that the likelihood of developing glaucoma and other eye diseases increases with age, so regular eye tests (at least every 2 years) are essential to ensure early diagnosis and optimum eye health.
How is glaucoma treated?
Treatment for chronic glaucoma is usually with eye drops. Laser treatment or surgery may be necessary in some cases. The good news is that once it is detected and treated, most people retain useful vision for a lifetime.
Glaucoma left untreated may lead to tunnel vision and, eventually, to blindness. It is estimated that approximately 2% of people over the age of 40 will have glaucoma. 13% of those on the blind register have glaucoma of some type.
Don't be a statistic – give yourself peace of mind.
Arrange an eye exam today!
The ciliary body, situated at the root of the iris, continually produces a fluid called aqueous humour. This is a clear, watery fluid that helps to maintain the normal shape of the eyeball. The nutrients in the Aqueous help sustain the structures within the eye that do not have a copious blood supply.
At the same time the aqueous humour is also draining from the eye via at a point called the angle - situated where the back of the cornea meets the anterior surface of the iris. In the angle is situated the trabecular meshwork. This is analogous to the plug-hole in a bath.
The Inflation pressure within the eye is the result of the difference between the rate of fluid being secreted by the ciliary processes and the rate of drainage through the trabecular meshwork.
The inflation pressure or "intra-ocular pressure" or IOP, varies considerably within the normal population, between about 10mm.Hg. (soft) and 21 mm. Hg. (hard).
Glaucoma
Glaucoma is the name given to a group of conditions in which the pressure within the eye builds up to a level such that it compresses the blood vessels supplying the optic nerve, causing nerve fibres to die off irreversibly.
Progressive loss of the patient's field of vision may not be noticed by the patient for years in the slowly developing, chronic form of glaucoma.
In the rarer acute form, because the patient experiences symptoms such as a painful red eye, haloes round lights and nausea, it is usually detected soon after onset.
If the iris blocks off the fluid suddenly, this is acute glaucoma (acute - sudden).
The hard eye gets very painful and red with a hazy surface and misty vision. The mistiness may cause coloured haloes to be seen around lights.
If the hardness happens slowly by 'silting up' of the sieve tissue, this is chronic open angle glaucoma (chronic - slow). The eye adjusts partially to the raised eye pressure and the patient may not notice anything wrong until blood supply of the nerve of sight (the optic nerve) is slowly cut off by the pressure on it, causing blank patches in the field of vision. Occasionally, certain eyes may not tolerate even average pressures, such patients my require treatment to reduce their eye pressures to even lower levels. This is called 'low tension' glaucoma. By contrast some eyes tolerate higher than average pressures without loss of visual field. This is called 'ocular hypertension'. It does not usually require treatment but should be carefully reviewed at intervals.
Are there other types of glaucoma?
Yes. It can be due to inflammation or other trouble in the eye which obstructs the normal flow of fluid through the eye (secondary glaucoma). It can also occur in babies due to the eye not forming properly.
Some type of glaucoma occurs in about 2% people over the age of 40. Most cases in the western world are of the chronic type.
Is it hereditary?
Yes, chronic glaucoma is about 10 times as common in near blood relations, so all those relative from the age of about 35 should have their eye pressures measured and their optic nerves viewed with an ophthalmoscope. If these tests are abnormal an examination of the visual fields becomes essential. These measures should make sure that the presence of glaucoma is not being overlooked.
Can it be successfully treated?
Yes, it can be controlled and further loss of sight prevented in the majority of patients. Treatment is by eyedrops, tablets, laser light beam, or operation.
a) The 'sudden' type of glaucoma requires urgent hospital treatment and a small operation or laser treatment but if there is no delay in starting treatment, restoration of sight may be almost complete. Delay may be disastrous.
b) In the 'slow' type of glaucoma, treatment aims to prevent further loss of sight because as a rule what has been lost is not recovered. Early diagnosis is therefore of crucial importance.
Why do the persons with the 'slow' type of glaucoma not notice that there are black patches in their vision?
There are two reasons:
a) Because most people use both eyes together and one of 'fills in for the other.
b) Because the blank patches are not at first in the centre of their sight.
There is a loss of 'all round' vision and in some cases it is so restricted that it is like 'looking through a tube'. Frequently even this is not noticed until a very late stage.
Will I have it for life?
Usually the glaucoma tendency is always present and requires treatment but occasionally treatment can be discontinued gradually. This can only be decided by the ophthalmologist.
What happens if it is untreated?
Eventually, you may only see the Centre of what you are looking at, making it difficult to get about despite the sight being clear in the Centre. Later even this sight may be lost.
The centre of the optic nerve head becomes damaged when the intra-ocular pressure remains high enough to cut of the blood supply to it. The exact pressure that this occurs at varies from individual to individual. As the normal tissue dies off the disc looses its normal healthy colour and becomes much paler. An interesting fact is that this appearance in itself is not diagnostic as several normal, non-glaucomatous people, especially short-sighted ones, can have an optic disc appearance which mimicks that seen in glaucoma.
