Treatment

U An acute glaucoma attack is an emergency, and the patient requires immediate treatment by an ophthalmologist. The underlying causes of the disorder require surgical treatment, although initial therapy is conservative.

Medical therapy. Goals ofconservative therapy:

❖ Decrease intraocular pressure.

❖ Allow the cornea to clear (important for subsequent surgery).

Time factor in reducing intraocular pressure:

Principles of medical therapy in primary angle closure glaucoma (see Fig. 10.3): ❖ Osmotic reduction in the volume of the vitreous body is achieved via systemic hyperosmotic solutions (oral glycerin, 1.0-1.5 g/kg of body weight, or intravenous mannitol, 1.0-2.0 g/kg of body weight).

Conservative treatment

Within six hours

Not within six hours

Surgery the next day

Immediate surgery

❖ Production of aqueous humor is decreased by inhibiting carbonic anhy-drase (intravenous acetazolamide, 250- 500 mg). Both steps are taken initially to reduce intraocular pressure to below 50-60 mm Hg.

❖ The iris is withdrawn from the angle of the anterior chamber by administering topical miotic agents. Pilocarpine 1 % eyedrops should be applied every 15 minutes. If this is not effective, pilocarpine can be applied more often, every five minutes, and in concentrations up to 4%. Miotic agents are not the medications of first choice because the sphincter pupillae muscle is ischemic at pressures exceeding 40-50 mm Hg and willnot respond to miotic agents. Miotic agents also relax the zonule fibers, which causes anterior displacement of the lens that further compresses the anterior chamber. This makes it important to first initiate therapy with hyper-osmotic agents to reduce the volume of the vitreous body.

❖ Symptomatic therapy with analgesic agents, antiemetic agents, and sedatives may be initiated where necessary.

Mechanical indentation of the cornea: Simple repetitive indentation of the central cornea with a muscle hook or glass rod for approximately 15-30 seconds presses the aqueous humor into the periphery of the angle of the anterior chamber, which opens the angle. If this manipulation succeeds in keeping the trabecular meshwork open for a few minutes, it will permit aqueous humor to drain and reduce intraocular pressure. This improves the response to pilocarpine and helps clear up the cornea.

Surgical management (shunt between the posterior and anterior chambers). Once the cornea is clear, the underlying causes of the disorder are treated surgically by creating a shunt between the posterior and anterior chambers.

Neodymium:yttrium-aluminum-garnet laser iridotomy (nonincisional procedure): The Nd:YAG laser can be used to create an opening in the peripheral iris (iridotomy) by tissue lysis without having to open the globe (Figs. 10.18 a-c). The operation can be performed under topical anesthesia (Fig. 10.19).

Peripheral iridectomy (incisional procedure): Where the cornea is still swollen with edema or the iris is very thick, an open procedure may be required to create a shunt. A limbal incision is made at 12 o'clock under topical anesthesia or general anesthesia, through which a basal iridectomy is performed. Today peripheral iridectomy is rarely performed, in only in 1 - 2% of all cases.

Prophylaxis: When the patient reports clear prodromal symptoms and the angle of the anterior chamber appears constricted, the safest prophylaxis is to perform a Nd:YAG laser iridotomy or peripheral iridectomy. If one eye has already suffered an acute attack, the fellow eye should be treated initially every 4-6 hours with pilocarpine 1% to minimize the risk of a glaucoma attack. The second eye should then be treated with a Nd:YAG laser to prevent glaucoma once surgical stabilization of the first eye has been achieved.

Fig. 10.18 a The pupillary block (asterisk) prevents the outflow of aqueous humor into the anterior chamber. The pressure in the posterior chamber increases (red arrows), and the peripheral iris is pressed against the trabecular meshwork. This blocks drainage of the aqueous humor and creates an acute angle closure (arrow). b A Nd:YAG laser beam focused through a contact lens burns a circumscribed hole in the tissue of the iris to create a shunt between the posterior and anterior chambers (arrow). This permits the aqueous humor to flow into the anterior chamber despite the persisting pupillary block (asterisk).

c The aqueous humor trapped in the posterior chamber now flows through this newly created opening in the iris, equalizing the pressure in the two chambers and circumventing the pupillary block. The iris recedes into its normal position, the trabecular meshwork (arrow) is opened again, the aqueous humor can drain normally, and normal intraocular pressure is restored. No future pupillary block can form following Nd:YAG laser iridotomy.

Fig. 10.18 a The pupillary block (asterisk) prevents the outflow of aqueous humor into the anterior chamber. The pressure in the posterior chamber increases (red arrows), and the peripheral iris is pressed against the trabecular meshwork. This blocks drainage of the aqueous humor and creates an acute angle closure (arrow). b A Nd:YAG laser beam focused through a contact lens burns a circumscribed hole in the tissue of the iris to create a shunt between the posterior and anterior chambers (arrow). This permits the aqueous humor to flow into the anterior chamber despite the persisting pupillary block (asterisk).

c The aqueous humor trapped in the posterior chamber now flows through this newly created opening in the iris, equalizing the pressure in the two chambers and circumventing the pupillary block. The iris recedes into its normal position, the trabecular meshwork (arrow) is opened again, the aqueous humor can drain normally, and normal intraocular pressure is restored. No future pupillary block can form following Nd:YAG laser iridotomy.

— Nd:YAG laser iridotomy.

— Nd:YAG laser iridotomy.

Fig. 10.19 The Nd:YAG laser opening in the iris (arrow) creates a shunt between the posterior and anterior chambers.

Prognosis: One can usually readily release a pupillary block and lower intraocular pressure in an initial attack with medication and permanently prevent further attacks with surgery. However, recurrent acute angle closure glaucoma or angle closure persisting longer than 48 hours can produce peripheral synechia between the root of the iris and the trabecular meshwork opposite it. These persisting cases of angle closure glaucoma cannot be cured by Nd:YAG laser iridotomy or iridectomy, and the angle closure will persist despite surgery. Filtration surgery is indicated in these cases.

H Where intraocular pressure is controlled and the cornea is clear, gonios-copy is indicated to demonstrate that the angle is open again and to exclude persistent angle closure.

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