Glaucoma in Asia: regional prevalence variations and future projections

Methodological quality of the review: Low confidence

Authors: Chan EWE, Li X, Tham YC, Liao J, Wong TY, Aung T and Cheng CY

Geographical coverage: Asia

Sector: Glaucoma.

Sub-sector: Glaucoma

Equity focus: No

Review type: Other review

Quantitative synthesis method: systematic review

Qualitative synthesis method: Not applicable

Background:

Glaucoma is a leading cause for irreversible visual impairment and blindness worldwide. Asia alone accounts for almost 60% of the world’s total glaucoma cases. The group recently reported on global glaucoma prevalence, as well as continent-specific glaucoma prevalence in Africa, North America, Latin America, Europe and Asia. Similarly, they found that glaucoma burden disproportionally affected people residing in Asia compared with other regions of the world. Nevertheless, the authors’ earlier study did not evaluate the variation of glaucoma prevalence across different Asian subregions. Furthermore, estimates of secondary glaucoma were also not calculated in the earlier work, as secondary glaucoma data were largely not available in Western and African population-based studies. Hence, to accurately assess sub-regional variations in the prevalence of glaucoma overall or its subtypes, a further analysis that takes into consideration differences in regional population structures is needed.

Objectives:

The review aimed to estimate the prevalence and future projection of glaucoma, including its subtypes, in different subregions across Asia using the hierarchical Bayesian (HB) approach.

Main findings:

A total of 30 articles from 23 population-based studies reporting glaucoma prevalence in Asia for inclusion in the meta-analysis. In brief, there were 10 studies from East Asia, Japan, South Korea and Mongolia, nine studies from South-Central Asia (India, Nepal, Iran and Sri Lanka, five studies from South East Asia (Singapore, Myanmar and Thailand) and one study from West Asia (Qatar). In all, the included data involved 1,318 POAG cases in 66,800 individuals, 691 PACG cases in 72,767 individuals and 103 secondary glaucoma cases in 38,029 individuals.

The pooled prevalence of glaucoma overall was 3.54% (95% credible interval (CrI) 1.83 to 6.28) in adult Asians. Among the glaucoma subtypes, the prevalence of primary open-angle glaucoma (POAG) was highest (2.34%; 95% CrI 0.96 to 4.55), followed by primary angle-closure glaucoma (PACG) (0.73%; 95% CrI 0.18 to 1.96) and secondary glaucoma (0.47%; 95% CrI 0.09 to 1.48). The prevalence of glaucoma overall was similar across subregions, ranging from 3.40% in West Asia to 3.70% in East Asia. East Asia had the highest prevalence of PACG (1.07%; 95% CrI 0.28 to 2.74) compared with the rest of the other Asian subregions.  Bayesian meta-regression showed that the odds ratio (OR) of PACG was 5.55 (95% CrI 1.52 to 14.73) in East Asia compared with South East Asia after adjusting for age and gender.

After adjusting for age, men were more likely to have POAG (OR 1.37, 95% CrI 1.17 to 1.59) and less likely to have PACG (OR 0.54, 95% CrI 0.41 to 0.71) compared with women. Bayesian meta-regression analysis showed that only POAG was significantly more prevalent in people living in urban areas (OR 2.11, 95% CrI 1.57 to 2.38) compared with people living in rural areas after adjusting for age and gender.

Across Asia, East Asia had the highest number of people with glaucoma (25.20 million), followed by South-Central Asia (17.06 million) and South East Asia (6.92 million). The number of people with glaucoma in Asia is estimated to increase by 16.0% to 59.51 million in 2020, and by 57.6% to 80.87 million in 2040.

Methodology: 

Inclusion criteria:

• population-based study of POAG, PACG or secondary glaucoma from a defined geographic region in Asia;
• clear definition of random or clustered sampling procedure;
• response rate ≥70%;
• visual field testing with either automated static or frequency doubling perimetry at least among glaucoma suspects;
• optic disc evaluation by an ophthalmologist;
• anterior chamber angle evaluation by gonioscopy at least among glaucoma suspects; and
• glaucoma defined using the International Society for Geographical & Epidemiological Ophthalmology (ISGEO) criteria.

Search criteria:

The Meta-analysis of Observational Studies in Epidemiology was used for this study. Research was done on the electronic databases of PubMed, Medline and Web of Science for relevant published research articles, letters, review articles and abstracts. It was conducted from the 23th October 2013 with an updated on 31 December 2013 with articles dating from January 1960.

Two investigators (EWC and Y-CT) independently selected the studies and applied the inclusion and exclusion criteria. Disagreements were resolved by consensus or adjudication by the senior author (C-YC).

The following information was extracted from each study: study location, year of publication, year of study conducted, response rate, age groups, gender, habitation type, geographic subregion and the prevalence of POAG, PACG and secondary glaucoma. Glaucoma was defined based on clinical findings indicating the following entities: pseudo exfoliation, rubeotic, steroid-induced, traumatic and pigment dispersion glaucoma.

Analysis:

An HB model was constructed to perform meta-analysis to determine the prevalence of POAG, PACG, secondary glaucoma and all glaucoma combined in Asia. The logit of prevalence was modelled using a normal distribution with mean of a linear combination of covariates that varies across studies (using gender, geographic subregion, habitation type). The overall age ranges of different studies were mapped to the same age range (40 to 80) to ensure the pooled prevalence was comparable between various subregions or rural/urban habitation, by centring the lower bound of age range to 40 and upper bound to 80.

The estimated prevalence rates were assumed constant over the next 27 years for our projection to year 2040. This assumption was supported by the authors’ Bayesian meta-regression analysis that suggested no significant change in glaucoma prevalence with year of study conducted (OR 0.98, 95% credible intervals (CrI), 0.94 to −1.03. Bayesian meta-regression model was used to model associations of the logit of POAG and PACG prevalence. Gender-specific and age-specific prevalence data were used in the meta-regression to estimate the OR of PACG and POAG and to exam the pooled effects on PACG and POAG from age, gender, geographic subregion and habitation type. Age-gender-adjustment was performed in the met regression. Statistical analyses were performed using JAGS software (V.3.3.0) running from R V.3.0.2 (R Development Core Team, 2013) to implement Markov chain Monte Carlo technique for geographic subregion and habitation type, respectively, which were all considered as fixed effects.

Applicability/external validity:

The results of this review are specific for Asian countries although the authors acknowledge some limitation: the lack of age specific and gender-specific data from several studies, the prevalence estimates for West Asia used data from the Qatar Eye Study only. Nonetheless, the methodology of this review can be applied in other setting as Africa, Europe or America.

Geographic focus:  

This review focuses on Asian countries and both high-income countries and low- to middle-income settings in Asia. The authors acknowledge some limitation highlighted above but they mention that, considering the geographic proximity between South and Central Asia, and the larger demographic of South Asia in that subregion, it may be reasonable to extrapolate the estimates of South Asia to the entire subregion in order to provide the best available estimate for this subregion.

Summary of quality assessment:

Overall, there is low confidence in the conclusions about the effects of this review. It is not clear from the review if there were any restrictions applied on the inclusion of studies based on publication or language status. It is not clear the risk of bias of included studies, impacting on the reliability of the overall findings of the review.