In our present study, POAG accounted for 69.3% of glaucoma cases and PACG accounted for only 5.3% cases. The finding of a lower prevalence of PACG in Malays compared with Chinese people in Singapore from the Tanjong Pagar Study (POAG:PACG; 50%:30%)
4 is consistent with hospital data showing that Malays had a rate of acute, symptomatic angle-closure that was half that of the Chinese population.
29 Nonetheless, a PACG prevalence of 0.12% in Malay people in this study is considerably lower than one would expect, considering the results in other studies. A study performed on the Cape people of South Africa of predominantly Southeast Asian origin (many of whom originated from Malaysia and Indonesia) found a higher rate of PACG compared with POAG (2.3% vs. 1.5%), although the definition of PACG used in this study included subjects with previous acute or intermittent symptoms of angle closure.
30 The relative proportions of glaucoma attributable to POAG and PACG found in our study were comparable to that in the Japanese
23 24 and Irish populations
31 but differed significantly with rates in the other Asian data and may not be entirely applicable to the Malay population living outside Singapore
(Table 4) . It is possible that the lower prevalence of PACG is an underestimate due to the limited amount of gonioscopy performed in our study and the Tajimi study.
23 24 In both studies, the van Herick technique was used to screen for participants with a shallow peripheral anterior chamber who then proceeded to undergo gonioscopy. Although the van Herick technique has been sensitive in screening for occludable angles,
21 cases of occludable angles and PACG can still be missed. In this study, we used a less stringent definition for occludable angles (posterior trabecular meshwork seen for <180° of the angle circumference) in contrast to the ISGEO definition (posterior trabecular meshwork seen for <90° of the angle circumference) that was used in Mongolia, Singapore, and Guangzhou.
5 25 32 A recent study has suggested that the latter definition may be too strict and cause an underestimate of angle closure, as eyes with lesser extent of closure may still have PAS.
33 Besides our study, the Chennai Glaucoma study also used the 180° definition.
9 25 Regardless, further analysis on variations in ocular dimensions, axial length, and anterior chamber depth is needed to explore reasons for the low prevalence of PACG in Malays.