An abrupt blockage of the drainage system in the eye, causing a painful, rapid rise in fluid pressure
Normally, the fluid that is secreted into the front of the eye to maintain the eye’s shape and nourish the tissues drains away continuously. However, in acute (narrow-angle) glaucoma, the drainage system suddenly develops a blockage, and the fluid pressure inside the eye rises rapidly. Acute glaucoma is a medical emergency requiring prompt treatment. Left untreated, the eye can swiftly become damaged and a permanent reduction in vision can result.
The fluid in the front part of the eye is produced continuously by a ring of tissue called the ciliary body, behind the eye’s coloured iris. Normally the fluid flows out through the pupil and drains away through the trabecular meshwork, which surrounds the iris. This sieve-like meshwork is situated deep within the drainage angle, which is found between the outer rim of the iris and the edge of the cornea. In acute glaucoma, the iris bulges forwards and closes the drainage angle, trapping fluid within the eye. The pressure inside the eye rises as more fluid is secreted. As the pressure rises, it may damage the nerves in the light-sensitive retina and in the optic nerve, which carries nerve signals to the brain, causing impairment of vision.
Having a smaller eyeball than usual is a common cause of longsightedness (see Hypermetropia), and increases the risk of developing acute glaucoma. The disorder is more common in older people because the lens of the eye grows throughout life and may eventually press against the iris. Fluid builds up behind the iris, which bulges forwards and blocks the drainage angle.
Acute glaucoma can be triggered when dim light causes the pupil to widen. The iris thickens and the drainage angle can close. Acute glaucoma sometimes runs in families and is more common in women and in people of Asian descent.
A full-blown attack of acute glaucoma may be preceded by mild attacks in the weeks before. Mild attacks usually take place in the evening. Symptoms include pain in the eyes and haloes appearing around lights; the symptoms are relieved by sleeping. If you have these symptoms, you should consult your doctor at once. Full-blown attacks develop suddenly. Symptoms include:
Rapid deterioration of vision.
Intense pain in the eye.
Redness and watering of the eye.
Sensitivity to bright light.
Haloes appearing around lights.
Nausea and vomiting.
If you develop a painful eye or your vision deteriorates suddenly, go to an accident and emergency department or consult your doctor immediately.
The pressure inside the eye is measured using a technique such as tonometry. If acute glaucoma is detected, you will be given immediate drug treatment by intravenous injection, as eyedrops, and possibly also by mouth to reduce the pressure in the eye (see Drugs for glaucoma). Laser iridotomy will probably be performed as soon as the pressure falls. In this technique, a laser is used to make a small hole in the iris so that fluid can be released. The unaffected eye may also be treated as a precaution.
After surgery, most people are symptom-free, but some loss of the outer edges of vision may remain. Long-term drug treatment or a second operation may be needed to prevent loss of sight.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.