Tuesday, December 12, 2006

Section 9-D: Treatment of acute angle closure glaucoma

Intraocular pressure may be critically high in acute angle closure glaucoma. The goals of treatment are to lower the pressure as soon as possible and to prevent further attacks. Initially, acute angle closure glaucoma is treated with a range of medicines that may be given as eye-drops or pills. In rare cases intravenous medications may also be used. However, the definitive treatment for most cases of angle closure glaucoma is laser peripheral iridotomy.

In most cases of angle closure glaucoma, medications are used first to lower the eye pressure to a point at which the laser peripheral iridotomy (see Chapter 8-A-2) can safely be performed. While medications may temporarily treat an episode of acute angle closure, laser peripheral iridotomy is necessary to definitively treat and prevent future attacks. The treatments for acute angle closure glaucoma are discussed in more detail below:

Topical medications. Most of the same eye-drops that are used for chronic forms of glaucoma (chapter 7) are also used to treat acute angle closure glaucoma. The combined use of several medications are generally required to sufficiently lower intraocular pressure.

Three classes of medications reduce the production of aqueous fluid (beta blockers, alpha adrenergic agonists, and carbonic anhydrase inhibitors) and thereby lower pressure in the eye. These aqueous suppressant medications are useful in lowering the pressure in acute angle closure glaucoma. Rapid application of a series of beta blockers, alpha adrenergic agonists, and carbonic anhydrase inhibitors eye drops will often lower intraocular pressure sufficiently to to allow definitive treatment with a laser (see below).

Once the eye pressure has been lowered with other medications, cholinergic eye drops may be used to pull the iris centrally in preparation for a laser treatment. The cholinergic eye-drops stretch the iris and make it easier for the laser to produce a hole in the iris (see below).

Oral medications. When topical eye-drops fail to lower intraocular pressure to safe levels, oral medications may be necessary in treating acute angle closure glaucoma. Two forms of oral carbonic anhydrase inhibitors (acetazolamide and methazolamide) can be used to treat acute angle closure glaucoma by reducing the production of aqueous fluid. Occasionally, a hyperosmotic drug (glycerol or isosorbide) may be used. The latter medications help to draw fluid out of the eye and into the bloodstream, thereby lowering the IOP.

Intravenous medications. Intravenous medications may rarely be necessary when topical and oral medications fail to adequately lower the intraocular pressure or when a patient is too sick to take oral medications. Intravenous hyperosmotics (urea or mannitol) may be used in these situations.

Laser treatment (Laser Peripheral Iridotomy). A laser peripheral iridotomy to break the pupillary block and acute closure of the drainage angle should be performed as soon as possible after using medications. The goal of a laser peripheral iridotomy is to produce a hole in the iris to relieve the papillary block and allow aqueous fluid to make its way to the trabecular meshwork, thereby lowering the IOP (Figure 9-4).


Angle closure glaucoma

Laser Peripheral Iridotomy

Figure 9-4. Laser Peripheral Iridotomy. The definitive treatment for acute angle closure glaucoma is laser peripheral iridotomy. A. Normal flow of aqueous humr in an eye with an open drainage angle. B. In acute angle closure glaucoma aqueous humor cannot pass through the pupil (pupillary block). Fluid collects behind the iris causing it to bow forward and close the drainage angle. The obstruction of aqueous humor drainage causes a rapid rise in intraocular pressure. C. The treatment for acute angle closure glaucoma using the laser to produce a hole in the iris (laser iridotomy). D. Aqueous humor can bypass the pupil and make its way to the trabecular meshwork and out of the eye. Bypass of the pupillary block reduces bowing of the iris and opens the drainage angle.



The small hole in the iris created by laser peripheral iridotomy is not easily recognized by the naked eye but is easily seen by an ophthalmologist during an eye exam (Figure 9-5).




Figure 9.5 Laser peripheral iridotomy

Figure 9-5. Laser peripheral iridotomy (LPI). The laser treatment for acute angle closure glaucoma creates a small hole in the iris (arrow) that is visible with an eye examination.

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