Glaucoma

A condition in which the pressure of the fluid in the eye is abnormally high, causing the compression and obstruction of the small blood vessels that nourish the retina. This may result in nerve fibre destruction and gradual loss of vision. The most common form of glaucoma is chronic simple (open-angle) glaucoma, which rarely occurs before age 40 and often causes no symptoms until visual loss is advanced. It is caused by a gradual blockage of the outflow of aqueous humour over a period of years, causing a slow rise in pressure. The condition tends to run in families. In acute (closed-angle) glaucoma, there is a sudden obstruction to the outflow of aqueous humour from the eye and the pressure rises suddenly. This causes a severe, dull pain in and above the eye, fogginess of vision, and the perception of haloes around lights at night. Nausea and vomiting may occur, and the eye may be red with a dilated pupil. Congenital glaucoma is due to an abnormality in the drainage angles of the eyes before birth. Glaucoma can also be caused by eye injury or a serious eye disease such as uveitis or lens dislocation. Applanation tonometry is used to check for glaucoma by measuring the pressure within the eye. An ophthalmoscope may show depression of the head of the optic nerve due to the increase in pressure. Visual field testing will be needed to assess whether vision has already been damaged, because longstanding or severe glaucoma can result in loss of peripheral vision (see tunnel vision). Prompt treatment is essential to prevent permanent loss of vision. Chronic simple glaucoma can usually be controlled with eye-drops (e.g. timolol) or tablets that reduce pressure in the eye. Treatment needs to be continued for life. If drugs are ineffective, surgery may be needed to unblock the drainage channel or create an artificial channel. Acute glaucoma requires emergency drug treatment, often in hospital. Surgery, usually iridectomy, may be necessary to prevent a further attack.