Methodological quality of the review: Medium confidence
Authors: Liu W, Ling J, chen Y, Wu Y, Lu P
Region: America, Europe, Asia and Africa
Equity focus: None specified
Review type: Other review
Quantitative synthesis method: Meta-analysis
Qualitative synthesis method: Not applicable
The main risk of open-angle glaucoma (OAG) is considered to be elevated intraocular pressure (IOP) and other systematic risk factors, including older age, family history of OAG, diabetes mellitus, alcohol consumption, hypertension, and cigarette smoking. Studies have shown inconsistent results on the association between adiposity and glaucoma incidence.
Determine the potential association between adiposity and glaucoma incidence
Fifteen eligible studies involving 2,445,980 individuals were included to investigate the association between adiposity and glaucoma incidence. These consisted of nine cross-sectional studies, one case-control and five cohort studies. Six were conducted in America, seven in Asia and one in Africa and one in Europe. The quality scale for 11 of the studies was 8 or greater, which is considered to indicate a relatively high methodological quality and the remining four studies were scored less than 8.
The relative risks (RRs) were pooled with 95% confidence intervals (CI) by using a random-effects model. The pooled RR between adiposity and elevated intraocular pressure (IOP) was 1.73 (95% CI, 1.18–2.54), whereas that between adiposity and open-angle glaucoma (OAG) was 0.97 (95% CI, 0.83–1.13). The pooled RR between abdominal adiposity and glaucoma was 1.28 (95% CI, 1.15–1.41), whereas that between general adiposity and glaucoma was 1.09 (95% CI, 0.87–1.37). Results of subgroup analysis by sex indicated the association between adiposity and glaucoma in the female group (RR, 1.31; 95% CI, 1.05–1.64), but not in the male group (RR, 1.11; 95% CI, 0.77–1.60). The pooled RR of cohort studies and cross-sectional studies were 1.00 (95% CI, 0.84–1.20) and 1.22 (95% CI, 0.89–1.66), respectively.
Conclusions: adiposity has a higher risk of elevated IOP, and abdominal adiposity has a positive association with glaucoma, especially in female patients.
The authors conducted a systematic search in PubMed and ISI Web of Science before December 2016, using the following terms: (“metabolic syndrome” OR “overweight” OR “obesity” OR “adiposity” OR “body mass index” OR “BMI” OR “intra-abdominal fat” OR “waist hip ratio” OR “waist circumference” OR “Anthropometric”) AND (“glaucoma” OR “intraocular pressure” OR “ocular hypertension” OR “open-angle glaucoma” OR “normal tension glaucoma” OR “high tension glaucoma”). No restrictions were applied in terms of region and language, but these were restricted on studies written in English only. Citations for related articles were detected for additional publications.
Inclusion criteria consisted of research which: reports the association of adiposity, BMI, WC, or WHR with glaucoma, or elevated IOP; adopts a cohort, case-control or cross-sectional design; stratifies BMI, WC, or WHR into more than two stratifications; and presents the RR, odds ratio (OR), or original data that could calculate RR values.
Data extraction and quality assessment of included studies were conducted by two reviewers independently. Because there is no suitable standardized assessment method to assess the quality of observation studies, including cohorts, case-control, and cross-sectional design, for this meta-analysis, a quality assessment tool was designed according to MOOSE, STROBE, and references. The studies which were scored 8 or above on quality scales were considered to be of a relatively high methodological quality.
For meta-analysis, RR with 95% CI was assessed to determine the relationship between adiposity and glaucoma incidence. Subgroup analyses were carried out according to adiposity measurement and outcome definition. Statistical heterogeneity was evaluated across studies using the Q test and I2 tests. Sensitivity analyses were examined by deleting each study individually to evaluate the quality and consistency of the results.
The authors note that findings are not applicable to all general population, but to those with specific socio-demographic characteristics. However, overall adiposity has a higher risk of elevated IOP and abdominal positive association with glaucoma, especially in female patients.
The authors did not discuss or analyse findings in relation to low- and middle-income countries.
Summary of quality assessment:
Medium confidence was attributed in the conclusions about the effects of this study as important limitations were identified. The authors used appropriate methods to analyse the findings of included studies, to extract data of included studies and assess its risk of bias. However, it is not clear if the authors avoided selection bias whilst screening studies for inclusion in the review and literature searches were not comprehensive to ensure that all relevant studies were included in the review.