Iridotomy Health Dictionary

A group of disorders of the eye characterised by the intraocular pressure being so high as to damage the nerve ?bres in the retina and the optic nerve (see EYE) as it leaves the eye en route to the brain. The affected person suffers limitation of the ?eld of vision and on examination the optic disc can be seen to be cupped. The clinical signs depend on the rate and extent of rise in pressure.

Individuals most at risk have a family history of GLAUCOMA (especially among siblings), are myopic (short-sighted), or have diabetic or thyroid eye disease. People with a strong family history of the disease should have regular eye checks, including tonometry, from the age of 35 years.

Glaucoma is usually classi?ed as being either open-angle glaucoma or narrow-angle glaucoma.

Open-angle glaucoma is a chronic, slowly progressive, usually bilateral disorder. It occurs in one in 200 of people over 40 and accounts for 20 per cent of those registered blind in Great Britain. Symptoms are virtually non-existent until well into the disease, when the patient may experience visual problems. It is not painful. The characteristic ?ndings are that the intraocular pressure is raised (normal pressure is up to 21 mm Hg) causing cupping of the optic disc and a glaucomatous visual-?eld loss. The angle between the iris and the cornea remains open. Treatment is aimed at decreasing the intraocular pressure initially by drops, tablets and intravenous drug administration. Surgery may be required later. A trabeculectomy is an operation to create a channel through which ?uid can drain from the eye in a controlled fashion in order to bring the pressure down.

Narrow-angle glaucoma affects one in 1,000 people over 40 years of age and is more common in women. Symptoms may start with coloured haloes around street lights at night. These may then be followed by rapid onset of severe pain in and around the eye accompanied by a rapid fall in vision. One eye is usually affected ?rst; this alerts the surgeon so that action can be taken to prevent a similar attack in the other eye. Treatment must be started as an emergency with a topical beta blocker (see BETA-ADRENOCEPTOR-BLOCKING DRUGS) in eye drops with other drugs such as ADRENALINE or pilocarpine added as necessary. Dorzolamide, a topical anhydrase inhibitor, can also be used. ACETAZOLAMIDE, also an anhydrase inhibitor, can be given by mouth. In an emergency before surgery, MANNITOL can be given through an intravenous infusion; this is followed by surgery to prevent recurrence. Acute narrow-angle glaucoma occurs because the peripheral iris is pushed against the back of the cornea. This closes o? the angle between iris and cornea through which aqueous humour drains out of the eye. Since the aqueous humour cannot drain away, it builds up inside the eye causing a rapid increase in pressure.

Various types of LASER treatment – trabeculoplasty (‘burning’ the trabecular network); iridotomy (cutting holes to relieve pressure); and ciliary-body ablation by ‘burning’ – are sometimes used in preference to surgery.... glaucoma

a type of *laser whose active medium is a crystal of yttrium, aluminium, and garnet. It is used for cutting tissue, for example in lens *capsulotomy or *iridotomy. Specialized types (e.g. the *holmium:YAG laser) are used for various specific purposes....  yag laser