What is glaucoma?
Glaucoma is an eye condition where the nerve at the back of the eye (the optic nerve) is damaged. This can lead to loss of vision. In most cases, the damage to the optic nerve is due to an increased pressure within the eye. There are different types of glaucoma.
The eye and aqueous humour
The eye needs to keep its shape so that light rays are focussed accurately onto the retina. So, the bulk of the eye is filled with a jelly like substance called the vitreous humour. But, in front of the lens the eye is filled with a clear fluid called aqueous humour.Aqueous humour is made by cells that line the ciliary body. This fluid fills the front of the eye and gives a little outward pressure to maintain the shape of the eye. Aqueous humour also contains oxygen and sugars to nourish parts of the eye.医学 全在.线提供www.med126.com
The aqueous humour drains out from the eye into the bloodstream through the sieve-like trabecular meshwork. This is near the base of the iris. So, there is a constant production and drainage of aqueous humour.
What happens in primary open angle glaucoma?
In primary open angle glaucoma (just called 'glaucoma' from now on) there is a partial blockage within the trabecular meshwork. This restricts the drainage of aqueous humour. The reason why the trabecular meshwork becomes blocked and does not drain well is not fully understood. The pressure of the aqueous humour builds up if the drainage is faulty. But, this also increases the pressure on the back of the eye.
The increased pressure in the eye can damage the optic nerve (the main nerve of sight) and the nerve fibres running towards it from the retina. The retina contains the 'seeing' cells at the back of the eye. The damaged parts of the nerve and retina lead to permanent patches of vision loss. In some cases this can eventually lead to total blindness.
What is the difference between increased eye pressure and glaucoma?
Glaucoma means that part of the optic nerve is damaged, usually caused by increased eye pressure. But, about 1 in 5 people with glaucoma have eye pressures in the normal range. This is called 'normal pressure glaucoma'. In this condition the optic nerve is damaged by relatively low eye pressures. Other factors such as a poor blood supply may make the optic nerve sensitive even to modest pressure. In contrast, some people have an increased eye pressure with no ill effect to the optic nerve.
However, as a rule, if your eye pressure is high you have a much increased risk of developing glaucoma and visual loss.
Who gets primary open angle glaucoma?
In the UK, about 1 in 50 people over 40 have glaucoma. It is unusual in people under the age of 35. It becomes more common with increasing age. Glaucoma can affect anyone, but it is more common if you:
At first there are usually no symptoms. There is no pain or redness in the eye. Most people with glaucoma do not notice problems until quite a bit of visual loss has occurred. This is because the first part of the vision to 'go' is the outer (peripheral) field of vision. Central vision, used to focus on an object such as when we read, is spared until relatively late in the disease. Also, although glaucoma usually affects both eyes, it may not affect them equally. The better eye may 'fill in' for a while if the other eye starts to lose patches of visual field.
Some elderly people with glaucoma put their gradual failing vision down to 'just getting old'. They might not have had their eyes checked for many years and may needlessly lose their sight. Untreated glaucoma is one of the world's leading causes of blindness.
But, blindness can be prevented if glaucoma is diagnosed and treated early enough.
