The prevalence of POAG in Caucasian-Americans has been reported to be between 0.28% and 2.2%16, 19
whereas the prevalence of PACG has been documented as 0.09% among Caucasian-Americans over 40 years of age20
. Alaskan Eskimos in this age range, on the other hand, have a reported PACG prevalence of 2.65%, almost 30 times higher than that of Caucasian-Americans.21
In addition, population-based studies performed in China, Thailand, Taiwan, India, the Philippines, Singapore and Japan have found higher prevalence statistics for PACG than those reported in Caucasians.7, 10, 15, 22, 23
An anatomically narrow anterior chamber angle may be the most predictive factor in the development of occludable angles4
, and perhaps PACG, however there exists limited data on the prevalence of narrow angles in East Asian-American populations. A high prevalence of narrow angles has been reported in the Vietnamese-American population6
, but little data exists concerning Chinese-Americans.
Our results indicate that a large proportion (60.2%) of our Chinese-American population with glaucoma or glaucoma suspicion have gonioscopically narrow angles. These findings seem to agree with population-based data from Asia, which suggest a high prevalence of narrow angles in both the mainland14
and Singaporean Chinese12
populations (36.9% and 10.6% among those ≥ 50 years, respectively). Although the findings of the present study are not population-based, the relatively high proportion of narrow angles in our glaucoma and suspect populations may suggest that Chinese-Americans may have a similarly high prevalence of narrow angles compared to mainland or Singaporean Chinese.
The early identification of narrow anterior chamber angles is important, as primary angle closure glaucoma is a leading cause of irreversible blindness in many populations, including mainland Chinese.15
In current ophthalmologic practice, a laser peripheral iridotomy (LPI) is the routine recommended treatment for most patients with narrow angles. The treatment has been shown to increase the size and depth of the anterior chamber and open the angle in most patients with narrow angles.24, 25
The direct relationship between anterior chamber angle narrowing and both shortened axial length and increased lens thickness have been discussed in the literature at length.14, 26-29
Similarly, narrow anterior chamber angles have consistently been shown to correlate strongly with age and female gender both in mainland Chinese14, 28, 30
, and in other ethnic groups9, 20, 27
. Our population of Chinese-American glaucoma and suspect patients differs from those previously studied. Patients in our population with narrow angles were found to be significantly older, but not more hyperopic or more likely to be female compared to their open angle counterparts. Age was also found to be a significant predictor of narrow angles in our multivariate model, while gender and refraction were not.
If Chinese-Americans are phenotypically similar to mainland or Singaporean Chinese, it is reasonable to extrapolate that they are likely to have an increased prevalence of narrow angles and risk for PACG compared to many other ethnically different American populations. Although not population-based, our study targets angle status in those patients most likely to suffer glaucoma-related vision loss, namely those with glaucoma or glaucoma suspicion. Our data is also derived from all patients who were seen by a comprehensive ophthalmologist over a defined time period, which limits the study's potential for selection or referral bias.
The fact that our study population includes only Chinese-American patients with glaucoma or glaucoma suspicion also serves as a limitation, since there are no comparison populations within the same clinic. The study subjects are not population-based, and therefore should not be expected to represent the Chinese-American population at large. A cross-sectional, population-based analysis is a logical next step to evaluate the anterior chamber angle characteristics of this large, yet understudied population.
Our data suggests that a significant portion of Chinese-American patients with glaucoma or suspicion are at high risk for having narrow anterior chamber angles. This study should serve as a starting point for the continued evaluation of angle-closure glaucoma risk among Chinese-Americans.