Friday, June 02, 2006

Section 4-D: Angle Closure Glaucoma

Angle closure glaucoma (also called closed-angle glaucoma) may present very differently from open-angle glaucoma. In contrast to open-angle glaucoma which is mostly asymptomatic, (acute) angle closure glaucoma may present suddenly with pain, nausea, and decreased vision. As its name implies, the drainage angle is closed when examined with a gonioscopy lens. (figure 4-6)

Figure 4-6. The goniolens on the eye examining the drainage angle (same as Figure 1-4).

The mechanism of angle closure comes from a contact between the lens and iris. Once this contact occurs, aqueous fluid is unable to pass into the anterior chamber through the pupil. This is called pupillary block. (figure 4-7)
Figure 4-7. An open angle is shown on the left. Aqueous is free to pass between the iris and lens and drain through the trabecular meshwork. Pupillary block (angle closure) is shown on the right. Aqueous is trapped behind the iris which pushes it forward to obstruct the trabecular meshwork. (same as Figure 3-4)

The aqueous fluid then accumulates behind the iris and pushes the iris forward. The peripheral iris then obstructs the trabecular meshwork or drainage angle. The inability for aqueous to exit the eye creates an IOP elevation. This process may occur acutely or chronically. If the pressure rise is sudden, pain occurs. When it happens chronically, it may not be symptomatic. Occasionally the episodes of angle closure may occur intermittently. In these cases, patients may have episodic symptoms of blurry vision, eye pain or headache.
The risk factors for angle closure glaucoma are not the same as in open-angle glaucoma. Those at risk tend to have narrow angles. Patients who are older, female, hyperopic (farsighted), or from an Asian background tend to be at risk for angle closure glaucoma. Age tends to be a risk factor because the lens thickens over time leading to a higher likelihood of pupillary block. Hyperopia tends to occur in people with small eyes. These eyes tend to be crowded and more likely to develop pupillary block (this will be covered in more depth in Chapter 5).
For those at risk, pupil dilation may also cause a higher likelihood of angle closure. Pharmacologic pupil dilation, therefore, is contraindicated in patients with narrow, occludable angles (figure 4-8). Various over-the-counter and prescription medications are also contraindicated due to the same mechanism. Once definitive treatment (laser peripheral iridotomy) is administered, these are no longer contraindicated (see below).

Figure 4-8. The angle between the iris and cornea is very narrow. Usually this angle is 45º. The angle in this picture is approximately 10°.

In acute angle closure glaucoma, a patient may have pain, nausea/vomiting, headache, a red eye, cloudy cornea, a shallow anterior chamber, and elevated IOP. Glaucoma eye drops are given to decrease the IOP but a definitive treatment needs to be done to break or relieve the pupillary block. The definitive treatment for acute angle closure glaucoma is laser peripheral iridotomy (LPI; figure 4-9). This laser procedure places a hole in the iris to circumvent the pupillary block, thereby allowing the iris to fall back and open up the drainage angle. If a patient cannot sit for a laser procedure, such as in children, a surgical iridectomy may be performed in the operating room. The same procedure (iridotomy) should eventually be performed in the unaffected fellow eye to prevent an occurrence in that eye. Once the procedure is performed in both eyes, pharmacologic pupil dilation or medications are no longer contra-indicated. Patients may be dilated or take these medications without fear of future acute angle closure glaucoma.

Figure 4-9. Laser Perpheral Iridotomy (LPI).

Symptoms of angle closure may also occur intermittently. In these cases, LPI is beneficial in preventing intermittent attacks of angle closure. When angle closure glaucoma is noted in a chronic setting, LPI may or may not be beneficial. In these cases, elevated IOP may be treated with LPI, topical medications or filtering surgery as in POAG.

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