Primary angle closure glaucoma (PACG) is a leading cause of blindness worldwide. In China, it is estimated that nearly one in six individuals over the age of 50 has an angle appearance that puts him/her at risk of PACG and acute angle closure attacks. Asian populations are aging so the number of people with PACG will increase dramatically in the coming decades. While it is often said that Chinese populations (and others in East Asia) have ten times the risk of PACG as Europeans, the truth is that in carefully conducted studies the number is closer to four times as much, and nearly one in 200 Europeans over the age of 40 has PACG. PACG is often missed in these populations, and efforts must be taken to identify it so that needless loss of vision is avoided. Furthermore, it is essential that adequate evaluation is given to the higher risk populations (older persons, Asians, and in particular, older women).
In order to focus this chapter, I will first review the terminology used when referring to patients with PACG and then will discuss the epidemiology of PACG. The remainder of this chapter will cover diagnosis and treatment strategies for PACG. Terminology to describe PACG is confusing, and this lack of clarity influences how we think about the disease. Much of this confusion stems from the literature that developed when gonioscopy first became widely available in the 1950s. Little was known about PACG and the natural history of the disease, so a wide range of terms were used.
In order to allow for more uniform reporting, and to improve how we think about the mechanisms of angle closure, a new terminology was proposed and subsequently modified during a consensus panel meeting involving over 100 glaucoma specialists from around the world. There are currently four categories for describing persons with angle closure, three of which require specific gonioscopic findings. Each of these requires that the pigmented trabecular meshwork is blocked by iris (what is termed “iridotrabecular contact or ITC”) in at least one quadrant. There is no firm agreement on how many quadrants must have ITC for angle closure to be present, but current consensus appears to be that at least 180 degrees is required. The amount of ITC is determined in a dark room using a one mm beam on a bright setting while performing gonioscopy. Greater amounts of illumination (a long wide beam, for example) will allow light to enter the pupil which can artificially open the angle.
1. Primary Angle Closure Suspect (PACS): Some people are completely normal except for the fact that the anterior chamber angle has ITC on gonioscopy. There is no “disease” present, and no evidence of harm to the patient. The clinician is concerned by the appearance, but the IOP and the optic nerve are both normal, and there are no peripheral anterior synechiae. How much angle closure must be present to apply this categorization remains controversial, but I typically use 180 degrees or more. Gonioscopy is performed as above, having the patient look straight ahead and only modestly tilting the lens if the view is difficult. Again, this is a somewhat subjective evaluation, but there are no better approaches available. There is ongoing debate about whether or not all these persons require iridotomy to avoid the development of PACG or acute attacks.
2. Primary Angle Closure (PAC): This category includes people with ITC for 180 degrees or more as described above for PACS. Furthermore, these people have some evidence that the angle appearance is causing harm to the eye. More specifically, they have either peripheral anterior synechiae (PAS) or elevated IOP, but they do not have optic nerve damage and visual field loss. This condition is considered pathologic (although there is almost no long-term data on people with these findings), and most clinicians recommend laser iridotomy for these people.
3. Primary Angle Closure Glaucoma (PACG): This category requires the presence of ITC for 180 degrees or more, as described above, along with glaucomatous optic neuropathy and visual field loss. The glaucoma definition requires the same findings as one would expect for open-angle glaucoma.
3. Primary Angle Closure Attack: This presents with classic signs and symptoms. Patients have very elevated IOP, the angle is closed, the conjunctiva is red, the cornea frequently is cloudy, and the patient has eye pain and may have nausea and vomiting. PACG occurs in about 0.5% of whites and blacks over the age of 40, and about 1.5% of Chinese and Indian individuals in this age group, but is much more common in older populations. Recent studies indicate that even in high prevalence countries such as China, open angle glaucoma is more common than PACG. However, even though PACG accounts for about a third of all glaucoma cases in China, most of the 5.2 million people blind from glaucoma have PACG. Similar findings were reported for Asian Indians where 41% of those with PACG were blind in one or both eyes from PACG.
PACG is associated with relatively anterior lens position and a proportionally thicker lens, both of which result in a relatively shallow anterior chamber depth, one of the strongest risk factors for PACG. Affected eyes are frequently hypermetropic (although not uniformly so, and PACG frequently occurs in myopic individuals).
PACG is also associated with a short axial length and small corneal diameters and radii of curvature. Interestingly, even though PACG is more prevalent in China, one study found that Chinese, blacks and whites had similar mean anterior chamber depths, indicating that other factors (such as the response of the iris to various stimuli) may contribute to higher rates of PACG among Chinese.
While the ocular biometric parameters described are associated with the presence of PACG and acute attacks of angle closure, it is not clear if any of them predicts which PAC suspects would have a poor outcome if left untreated. Other important risk factors that are associated with PACG and AAC attacks are female sex, age, and race.
In order to review the treatment of angle closure I will discuss each of the four sub-categories separately.
1. PACS: As stated above, these individuals have no evidence of disease but have ITC when examined on gonioscopy. There is debate about how to manage such individuals, with some recommending observation and others recommending laser iridotomy (LI) even in cases of ITC for less than 180 degrees.
2. PAC: All those with PAC have evidence of ITC and the presence of either PAS or elevated IOP. There is uniform consensus that LI is indicated for these individuals to help relieve pupil block in order to both prevent acute attacks and to reduce the risk of further progression of angle closure.
3. PACG: Unless PAS are extensive and there is fear of causing a substantial IOP spike while attempting LI, the first procedure for diagnosed PACG is LI. PACG is then treated like any other form of glaucoma with medications, surgery, or a combination of both. If the angle opens after LI and it is possible to perform trabeculoplasty, this is also a treatment option.
4. Acute Primary Angle Closure: The mainstay of treatment of acute attacks remains medical therapy. This includes topical ocular hypotensives as well as oral or intravenous carbonic anhydrase inhibitors and in some cases hyperosmotic agents. Some have published findings that acute paracentesis can lower IOP rapidly, but this has the potential of causing damage to intraocular structures. Others have reported that laser iridoplasty can lower IOP acutely, but longterm data showing that this is more or less effective than medical therapy are not yet published. Certainly, if the IOP remains elevated after one to two hours, one can consider performing iridoplasty.
PACG is a leading cause of blindness worldwide. With current technologies, most clinicians can only identify at risk individuals with gonioscopy (Figure 1a and b, 2a and b). Gonioscopy is, therefore, a fundamental part of the evaluation of patients seeking eyecare and needs to be performed routinely. Management of PACG is different from management of open angle glaucoma. For patients to receive proper treatment, all clinicians must provide a complete evaluation of the anterior chamber angle.
Dr. Friedman is an Associate Professor at the Wilmer Eye Institute, John Hopkins University School of Medicine as well as an Associate Professor, Dept of International Health, Johns Hopkins University Bloomberg School of Public Health. He is an editorial board member of the Ophthalmology and Journal of Glaucoma.
Suggested Readings
- Congdon NG, Qi Y, Quigley HA, et al. Biometry and Primary Angle Closure Glaucoma among Chinese, White, and Black populations. Ophthalmology 1997; 104:1489-1495.
- Thomas George R, Parikh R, Muliyl J, et al. Five year risk of progression of angle closure to primary angle closure glaucoma: a population based study. Acta Ophthalmol Scand 2003;81:480-485.
- Gazzard G, Foster PJ, Devereux JG, Oen F, et al. Intraocular pressure and visual field loss in primary angle closure and primary open angle glaucomas. Br J Ophthalmol 2003;87:720-725.
- Aung T, Friedman DS, Chew PT, et al. Long-term outcomes in Asians after acute primary angle closure. Ophthalmology 2004;111:1464-1469.
- Friedman Ds, Chew PTK, Gazzard G, Ang LPK, et al. Long-term outcomes in fellow eyes after acute primary angle closure glaucoma in the contralateral eye. Ophthalmology (submitted for publication).
- Aung T, Ang LP, Chan SP, Chew PT. Acute primary angle-closure glaucoma: long-term intraocular pressure outcome in Asian eyes. Am J Ophthalmol 2001;131:7-12.
