Methodological quality of the review: High confidence
Author: Cheng JW, Zong Y, Zeng YY, Wei RL
Geographical coverage: India, Mongolia, Singapore, Thailand, Bangladesh, Japan, China, Myanmar, Oman, Sri Lanka, Nepal, Korea, Qatar, Iran
Sector: Primary angle closure glaucoma
Equity focus: Asian population
Review type: Other review
Quantitative synthesis method: Meta-analysis
Qualitative synthesis method: Not applicable
Background: Glaucoma is considered the leading cause of irreversible blindness worldwide, with Asians accounting for approximately half of the world’s glaucoma cases. It has also been accepted that primary angle closure glaucoma (PACG) is higher in Asians than Europeans and Africans, with over 80% of those with PACG in Asia.
Because PACG appears to cause blindness more frequently than primary open angle glaucoma (POAG), it is an important public health issue. The current understanding of PACG in Asian populations is based largely on previous studies, using inappropriate case definition of glaucoma.
Objectives: To summarise the available population-based studies reporting the prevalence of PACG consistent with the ISGEO definition requiring structural and/or functional evidence of glaucomatous topic neuropathy.
Main findings: 29 population studies met all the inclusion criteria and were used to calculate the best evidence PACG prevalence estimates in adult Asian populations. Seven studies were conducted in China, five in India, three in Singapore, two each in Japan, Korea and Nepal, and one each in Bangladesh, Iran, Mongolia, Myanmar, Oman, Qatar, Thailand and Sri Lanka. Fifteen studies (52%) were undertaken in rural, six (21%) in urban and eight (28%) in mixed populations. The age ranges of the studied populations were 30 years and over, with the majority of studies (n= 20, 69%) being 40 years and over, and the male portion of the populations ranging from 36% to 64%. Twenty-five studies (86%) used ISGEO definition for the diagnosis of PACG. Overall, 22 studies were rated as having low risk of bias, and seven were rated as having moderate risk of bias.
The overall pooled prevalence of PACG in those of adult Asians was 0.75% (95% CI, 0.58, 0.96). Ethnicity-specific pooled prevalence estimates were 0.97% (0.22, 4.27) in Middle East group, 0.66% (0.23, 1.86) in South East Asia group, 0.46% (0.32, 0.64) in India group, 1.10% (0.85, 1.44) in China group and 1.19% (0.35, 3.98) in Japan group, respectively.
Age-specific prevalence was 0.21% (0.12, 0.37) for those 40-49 years, 0.54% (0.34, 0.85) for those 50-59 years, 1.26% (0.93, 1.71) for those 60-69 years, and 2.32% (1.74, 3.08) for those 70 years or above. The overall female to male ratio of the PACG prevalence was 1.51:1 (95% CI 1.01, 2.28).
Overall, based on these findings, authors conclude that PACG affects approximately 0.75% adult Asians, increasing double per decade, with 60% of cases being female. The prevalence rates vary greatly by ethnic region.
Methodology: Studies were included if they met the following inclusion criteria:
Authors conducted a search of PUBMED and EMBASE from inception to 2014, hand-searched the reference lists of the relevant reviews and consulted reference lists of included articles to find additional studies. Three researchers independently screened studies for inclusion.
Three researchers independently extracted data of included studies including study information, basic study data and quality-related data and outcome measures. Risk of bias of included studies was assessed by three researchers independently, using a checklist developed from an existing tool assessing risk of bias in prevalence studies.
Authors calculated ethnic-specific pooled prevalence estimates of PACG, using a random-effects model, which included the dominant ethnic group of five regions in Asia: Middle East, South East Asia, India, China and Japan. Age- and gender-specific pooled prevalence estimates of PACG were also calculated. A random-effect meta-regression was built with ethnicity, age and gender. In addition, to attempt to control potential methodologic heterogeneity, a random-effects regression model was also used to evaluate sources of variability in the overall pooled-prevalence estimate, such as urbanicity, the definition of occludable angle and the individual risk-of-bias items. To determine the level of heterogeneity, I2 statistic was used.
Applicability/external validity: On the basis of the findings from this review, authors note that the prevalence of PACG in Asians, especially in East Asians and South East Asians, is higher than those in Europeans.
Geographic focus India, Mongolia, Singapore, Thailand, Bangladesh, Japan, China, Myanmar, Oman, Sri Lanka, Nepal, Korea, Qatar and Iran.
Summary of quality assessment: Overall, there is high confidence in the conclusions about the effects of this study as minor limitations were identified in the methods used to conduct the review. The authors used appropriate methods to identify, include and critically appraise included studies. The only minor limitation identified included not contacting authors/experts for further potentially relevant studies.
However, authors note publication bias as a limitation of this review. Thus, more population-based studies should be required to estimate the whole prevalence in Asian populations. Authors used appropriate methods to analyse the findings of included studies and no strong policy conclusions were drawn.