Friday, June 16, 2006

Section 5-B: Risk Factors for Primary Angle-Closure Glaucoma (PACG)

The primary angle-closure glaucoma (PACG) has several risk factors of its own. They include: older age, Asian race, female gender, hyperopia (far-sightedness), and positive family history.

  1. Older age: Like POAG, the older age increases the risk of PACG. One reason for this may be that as you get older, cataract (cloudy lens) develops which results in thickening and narrowing of the anterior chamber drainage angle (see Chapters 3 for the eye anatomy). The narrow drainage angle predisposes the patient for PACG.
  2. Asian race: The Asian populations (especially of Far Eastern extraction) are at a higher risk for developing PACG than the other races (see Chapter 2: Table 2-3). PACG exists in 0.3 ~ 2.7% of the adult Asian populations, while it exists in only 0.1 ~ 0.6% in other races (white, black and Hispanic adult population). The exact reason for this is unclear. However, smaller anterior chamber depth has been found to be associated with PACG (Fig. 5-2). It is possible that the Asian population as a group has smaller anterior chamber depth than other populations, thus increasing the risk for PACG.

A.

B.

Figure 5-2. Open and closed drainage angles.
A.
The drainage angle formed between the cornea and the iris is wide open to about 40˚. Aqueous fluid flows freely to the trabecular meshwork and out of the eye. Note the anterior chamber depth is large.

B. The drainage angle is closed. The iris and the cornea are in contact and block the flow of aqueous fluid to the trabecular meshwork. The fluid is trapped in the eye causing intraocular pressure to rise. Note the anterior chamber depth is small.

  1. Female gender: In PACG, females are more common than males. It is generally believed that females (compared to males) have smaller eyes and therefore, smaller anterior chamber and narrower drainage angle. These are in turn anatomical risk factors for development of PACG.

  1. Hyperopia (far-sightedness): Like female gender, far-sighted people tend to have smaller eyes compared to near-sighted people. Smaller eyes tend to have smaller anterior chamber depth and narrower drainage angle, increasing the risk of PACG.

  1. Positive family history of PACG: It has been reported that up to 20% of relatives of PACG patients have anatomically narrow drainage angle. It is generally believed that the eye size (like height) is inherited. If the small eye size (and therefore, narrow drainage angle) is inherited, this would explain the inheritability of PACG.

It is important to identify those who are at risk for development of PACG, because the rate of blindness from angle-closure glaucoma is higher than in POAG. There are on-going studies in Asia looking at best ways to screen for PACG in a large population. Until we know better ways to detect PACG early, our recommendation is to seek periodic ophthalmic evaluation by an eye doctor (Table 5-3).

Table 5-3 (same as Table 2-2). Recommended frequency of eye examinations by American Academy of Ophthalmology

Age group

No glaucoma risk factors

Glaucoma Risk factors

20-29

At least once during interval

Every 3-5 years

30-39

At least twice during interval

Every 2-4 years

40-64

Every 2-4 years

Every 2-4 years

65

Every 1-2 years

Every 1-2 years

In those patients who are susceptible for PACG (or have narrow drainage angles), taking certain medications (both prescription and over-the-counter) can precipitate an acute angle closure glaucoma attack. These medications contain ingredients that tend to dilate the pupil (as a side-effect). In susceptible patients with a narrow drainage angle (called an occludable angle), the pupil dilation can precipitate an acute angle-closure attack, often raising the IOP to very high levels (40-50 mmHg are not uncommon). It is important to ask the pharmacist and read the drug label thoroughly before taking these medications. If you are not sure, ask your eye doctor whether you are at risk for development of angle-closure glaucoma before taking the medication. Finally, several classes of drugs have been reported to cause acute angle closure, even in non-susceptible patients. For example, topiramate (Topamax) used in seizure and migraine disorders has been reported to cause acute angle closure glaucoma in patients who are typically not at risk. Other medications associated with angle closure glaucoma include tricyclic anti-depressants, serotonin-uptake inhibitors, and diuretics. It is important to monitor for glaucoma if you are taking one of these medications.

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