A condition in which the intraocular pressure (fluid pressure inside the eyes) causes impaired vision. Aqueous humour (watery fluid) is secreted into the front of the eye by the ciliary body (a structure behind the iris) to nourish the tissues and maintain the eye’s shape. Unneeded fluid drains away at the edge of the iris. In glaucoma, however, this excess fluid is not able to escape. It then creates compression and obstruction of the blood vessels that supply the optic nerve and the retina. This, in turn, can kill nerve fibres and cause steady loss of vision.
Types, causes and symptoms
The most commonly seen form of glaucoma is chronic simple (open angle) glaucoma. It hardly occurs before the age of 40, and seems to run in families. In this condition, the outflow of aqueous humour is slowly blocked over a period of years, creating a slow rise in pressure. There are usually no symptoms until visual loss is advanced.
In acute (closed angle) glaucoma, the outflow of aqueous humour is quickly blocked, and the pressure increases suddenly. This can cause an extreme, dull pain above and in the eye, fogginess of vision, and the perception of halos around lights at night. Vomiting and nausea can arise, and the eye can become red with a dilated pupil.
Congenital glaucoma is caused by an abnormality in the drainage angles of the eyes that occurs before birth. Glaucoma may also be caused by an eye disease such as lens dislocation or uveitis or by injury.
A less rarely seen form, called low-tension glaucoma or normal pressure, arises in those whose intraocular pressure is normal or only slightly raised but causes the same damage to the optic nerve and retina as excessively high fluid pressure. This condition is little understood; and it appears that the pressure although not considered to be excessive, is too much for the tissues to withstand, and therefore causes damage.
Tonometry is used to check for glaucoma by measuring the pressure in the eye. Ophthalmoscopy can show depression of the head of the optic nerve caused by the increased pressure. Tests of the visual field are necessary to assess whether vision has already been impaired, due to longstanding or severe glaucoma can lead to loss of peripheral vision. Early detection is of utmost importance, before there are any visible symptoms, and those with a family history of glaucoma should have regular eyetests and tonometry.
Immediate treatment is necessary to prevent permanent loss of vision. Chronic simple glaucoma can often treated with eye-drops or tablets that lower the pressure in the eye. Treatment should be carried out for life. If drugs are unsuccessful, laser or surgery treatment can unblock the drainage channel at the edge of the eyes.
Acute glaucoma needs emergency drug treatment, usually in hospital. Laser or surgery treatment can be necessary in order to stop another attack. This treatment could consist of removing a small part of the iris (a procedure called iridectomy) or creating one or more holes in the iris to facilitate the aqueous humour to drain more easily.
Treatment for normal-pressure glaucoma is the exact same as for open-angle glaucoma, but is intended to reduce the intraocular pressure to an even lower level than should be.