Epidemiologic studies

Epidemiologic studies address the entire spectrum of PAC disease in its three ‘suspect’, ‘closure’ and ‘glaucoma’ manifestations. The incidence and prevalence of PAC disease in a population are influenced by a number of factors, including the definitions used, and people’s age distribution, gender, racial make-up, range of refraction, and heredity.

Most individuals with narrow angles do not develop angle clo-

sure or glaucoma. As mentioned previously, anatomically narrow angles are found in 2–6% of eyes in the United States.39,40 In con-

trast, the prevalence of angle-closure glaucoma in the United States is probably less than 0.2% of the population. This suggests that, at most, only 1 of every 10 American whites with anatomically narrow angles will develop angle-closure glaucoma in his or her lifetime. In a population-based study in Hyderabad, India,Thomas and co-workers showed that, over a 5-year period, the risk of progressing from narrow angles (PAC suspects) to actual angle closure with

either elevated IOP or synechiae (PAC) was 22%, but none of their patients actually developed optic nerve damage (PACG).108,109 But,

of 337 patients from the same population with PAC followed for 5 years, the risk of progressing to actual PACG was 28%.43 In contrast, in one study in Olmsted County, Minnesota, the incidence of angle-closure glaucoma was 8.3 per 100 000 of the population 40 years of age and older.110 In this same study, 14% of participants were blind in at least one eye at the time of diagnosis and a further 4% became monocularly blind over a 5-year follow-up. Thus we see there is tremendous variability in the manifestations of this disease, many of which appear to be both population and diseasestage specific.

Primary angle-closure glaucoma with pupillary block occurs onefourth to one-tenth as frequently as does primary open-angle glau-

coma (POAG) among white individuals living in the United States and western Europe.111,112–115 One study states that PACG occurs

in 0.1% of whites older than 40 years of age and comprises about 6% of the total glaucoma cases.116 Within this group, angle-closure glaucoma affects fewer individuals of Mediterranean origin than of northern European origin.117 Primary acute angle-closure glaucoma

with pupillary block seems to occur less frequently in individuals of black African ancestry;118,119 those who are affected generally have a chronic asymptomatic form of the disease.118,120–123

Acute PACG, with pupillary block, occurs rarely in some east

Asian-derived populations, including Pacific islanders and American Indians,24,124,125 yet occurs frequently in other populations, includ-

ing Eskimos (Inuit) in such diverse places as Greenland,Alaska, and northern Canada.126–128 Alsbirk129 reported that 10% of Eskimo

women and 2.1% of Eskimo men over 40 years of age are affected

by PACG. In such south Asian countries as India and Sri Lanka, the prevalence of PACG is equal to that of POAG.130,131 Primary

angle-closure glaucoma appears to be relatively more common

among many eastern and south-east Asian peoples, including the Chinese, Malaysian, Burmese, Filipino, and Vietnamese.24,132,133

Most of these cases are asymptomatic PACG (so-called ‘creeping

angle-closure type’).134 Conversely, Japanese and Thai patients seem to have PACG less frequently than do other Asians.135–137

In Taiwan, the prevalence of PACG in a rural population was about 3%, with an additional 2% PAC suspects.138Angle-closure glaucoma is uncommon among those of Hispanic origin, averaging about 0.10%.139 In a study of a northern Italian population, a prevalence of PACG of 0.6% was found, but occludable angles were found in over 15%, which is higher than previous studies in Caucasian populations.140 In south India, there is a relatively low rate of PACG and

suspects with narrow angles (0.7% and 1.4% respectively); but among the PACG eyes, plateau iris was common.31,141,142

In descending order, the entire spectrum of PACG appears most prevalent among Inuit and Eskimos,143 then, those of southeast Asian heritage (especially Chinese, Filipino, Vietnamese), less so in those of European descent (although the prevalence varies from country to country), and least among those of African and Hispanic descent. In China and Singapore, for example, PACG is not only very prevalent – representing over one-third of the total

glaucoma – but it is the most common cause of bilateral glaucoma blindness, though outnumbered 2:1 by POAG disease.39,144–146

Ethnicity apparently also plays a role in the severity of PACG when it clinically presents. For example, Chinese Singaporeans are twice as likely to require hospitalization for PACG than Singaporean Indians or Malaysians, although identical medical resources are available to all three groups.147

This is a vast amount of information to keep track of, and is constantly evolving. It should be obvious that both PACG’s mechanisms and its natural history comprise a wide spectrum, with specific variations among different ethnic populations.148 A few salient summary facts are presented in Box 15-1, which highlights key points from this new abundance of epidemiologic data on PAC disease.

Demographic risk factors

Age

Classic reports noted that PACG with pupillary block occurs with greatest frequency in the sixth and seventh decades of life.111,150,151

Box 15-1  Salient points regarding epidemiology of primary angle

closure19,20,48,72,149

1.PACG is rare compared to occludable angles

For every 10 ‘occludable angles’ seen, there’s one case of PACG Gonioscopy (our only tool!) is a POOR predictor

Most ‘occludable’ eyes do NOT get glaucoma!

Are YAG peripheral iridotomies innocuous (cf. reported focal lens changes and endothelial loss)? With a possible long-term complication rate of only 5%, prophylactic iridotomies on 40 million ‘at-risk’ Chinese and Indians could still cause 2 million potential problems

2.Acute PACG is uncommon compared to chronic PACG

Expect one acute PACG for every three chronic PACGs: i.e., the majority of world glaucoma disease is comprised of both asymptomatic chronic PACG and POAG

There are two implications:

Most patients do not know they have disease

The same screening algorithms for assessing IOPs, disc changes and visual fields apply

3.Ethnic variabilities of the glaucomas

POAG: moderate variable incidence among Caucasians Chinese Hispanics Africans

PACG: large variable incidence among Caucasians urban Chinese Mongolians Inuit

Hence, the ratio of POAG to PACG varies:

Euros Africans Hispanics – 5 POAG:1 PACG Urban Chinese – 1 POAG:2 PACG

Mongolians – 1 POAG:3 PACG

4.PACG is the major cause of world glaucoma blindness!

China: 90% glaucoma-blind have PACG, i.e., 10 more blindness from PACG than POAG (although their incidence ratio is near parity, with 2 POAG:3 PACG!)

Of 60 million with glaucoma in the world, 1/3 have PACG – but 25% of these patients are blind (more than twice the POAG blind)