Management

Acute primary angle closure

The aims of the treatment of APAC are to achieve rapid control of IOP, so as to limit optic-nerve damage and eliminate pupil block. The patient should then be monitored for subsequent IOP elevation and development of PACG. The management should be tailored for the fellow eye as well.

Medical therapy

This aids the rapid reduction in IOP. Intravenous carbonic anhydrase inhibitors (e.g. acetazolamide) usually have a rapid IOP lowering affect. 500 mg of acetazolamide is usually given intravenously, together with an oral dose of 500 mg (if the patient is not vomiting). The side effects of acetazolamide include paraesthesia, drowsiness, confusion, loss of appetite, polydipsia, and polyuria. It can also cause metabolic acidosis and electrolyte disturbance, respiratory failure, and Stevens–Johnson syndrome (Lam et al., 2007). Therefore, it is important to test blood for urea and electrolytes.

The inflammation in the eye is controlled by topical steroids (e.g. dexamethasone 0.1% or prednisolone 1%). Topical IOP lowering medications (e.g. beta blockers and alpha2 adrenergics) should also be given. The patients can be in pain with nausea and vomiting, so analgesics and antiemetics should also be given as supportive measures. Also the patient should be laid supine to

prevent further forward movement of the lens (Choong et al., 1999).

Miotics usually open the angle by pulling the peripheral iris away from the angle. However, in some eyes, miotics may increase the axial lens thickness and loosen the zonules, allowing for anterior lens movement, and thereby inducing further angle closure (Kobayashi et al., 1999). Due to this, it is preferable to withhold pilocarpine until the IOP has been reduced. Usually the pressure is rechecked 1 h after the commencement of treatment and pilocarpine is given then (Choong et al., 1999).

After 2 h, if the IOP is still above 35 mmHg, a hyperosmotic agent (e.g. 20% mannitol 1–2 g/kg) should be given intravenously for over 45 min. If there is no vomiting oral hyperosmotic agent (e.g. glycerol 1 g/kg) may be given as an alternative. Due care must be given as acidosis, pulmonary edema, congestive heart failure, dehydration, and acute renal failure are all side effects of hyperosmotics. Glycerol may cause ketoacidosis in diabetics.

Argon laser peripheral iridoplasty (ALPI)

If there are contraindications to systemic medications or the IOP is still elevated after some time, the next stage is to perform an ALPI. It involves the placement of a ring of contraction burns on the peripheral iris to contract the iris stroma near the angle, mechanically pulling open the angle. This allows for the eye to become quiet before the

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definitive treatment of laser peripheral iridotomy (PI) can be carried out. It has the advantage of being able to be performed in eyes with relatively hazy corneas and shallow angles; also it avoids the risks of complications from systemic therapy especially in APAC patients who are usually elderly with coexisting medical conditions. ALPI also opens the angles in eyes with plateau iris (Ritch et al., 2004).

The laser is performed with either an argon or diode laser. Either an Abraham (+66 dioptre) or Wise lens (+103 dioptre) is used. The burns are placed at the iris periphery as close to the limbus as possible. If bubbles or charring occur, the laser energy should be reduced. Four to six burns are placed per quadrant for a total of two to four quadrants (spot size 200–500 mm, energy 100–400 mW, duration 0.2–0.5 s).

Complications of iridoplasty include corneal endothelial cell damage, iris atrophy, inflammation, and PAS.

In cases where laser iridoplasty is not available, immediate anterior chamber paracentesis has been proposed as an alternative procedure to rapidly lower the IOP in APAC (Lam et al., 2007).

Laser peripheral iridotomy (PI)

Once the IOP is controlled and the cornea has cleared sufficiently, a laser PI can be carried out. This eliminates the pupil block. In Asian eyes, (which usually have thick brown irides) sequential use of the argon and neodyuim: yttrium-aluminum- garnet (Nd:YAG) lasers are used to create a PI, allowing for less total laser energy (Lim et al., 1996). In Caucasian eyes, with thinner irides, Nd:YAG laser may only be used. Burns with a small spot size, short duration, and high energy are placed as far in the iris periphery as possible between 11and 2 o’clock positions. Care should be taken to avoid corneal burns.

First the iridotomy lens (Wise or Abraham’s) is placed on the eye and argon laser is used to place four to six spots of about 600 mW in an overlapping pattern. The centre is then deepened with the energy increasing to achieve patency (spot size 50 mm, energy 600–1400 mW, duration 0.01–0.1 s).

The PI is then enlarged with the Nd:YAG laser (power 1.4–6 mJ).

Complications of PI include corneal endothelial damage, hemorrhage, cataract formation, imperforate PI, glare, retinal burns, IOP spikes, and malignant glaucoma. The post laser spikes can be reduced with perioperative use of alpha-2 agonists like brimonidine or apraclonidine (Chen et al., 2001).

Lens extraction

Removal of the crystalline lens deepens the anterior chamber and widens the drainage angle. In one report, it had a success rate of about 70% even if the eyes have significant PAS. Also, there were fewer additional surgical interventions and sight-threatening complications compared to trabeculectomy (Ming Zhi et al., 2003).

The preliminary results of a randomized control trial comparing phacoemulsification and conventional argon laser PI after APAC has shown an IOP rise of 3.2% in the phacoemulsification group compared to 28.3% in the iridotomy group. Surgery was performed 773 days after aborting the APAC. The authors felt that phacoemulsification can be carried out soon after aborting APAC but was not without risk and felt a better option was to perform surgery about 4 weeks after APAC when the eye had settled down adequately and the IOP had not yet risen (Lam et al., 2007).

It is notable that lens removal does not remove the risk of angle closure in eyes with plateau iris syndrome (Tran et al., 2003).

Monitoring for subsequent IOP rise in eyes with APAC

In Caucasians, 70% of APAC is controlled by PI alone. However, in Asians, as many as 58% of eyes develop an increased IOP after resolution of the acute event. 77% of these eyes developed the increase within 6 months of the acute episode and 33% required glaucoma filtering surgery (Aung et al., 2001). These eyes require long-term follow up, especially those with optic-nerve damage, W50% PAS, failure of initial medical therapy to