The association between gout and cataract risk: A meta-analysis

Methodological quality of the review: Medium confidence

Author: Luo C, Chen X, Jin H, Yao K.

Region: United States of America (USA) and Australia.

Sector: Age-related cataract

Sub-sector: Gout, risk

Type of cataract: Age-related cataract

Equity focus: None specified

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Gout is a chronic disease characterized by the deposition of monosodium urate crystals, which form in the presence of increased urate concentrations. Previous studies have focused on the association between gout and cataract formation. However, the results of these studies have been inconclusive.

Research objectives:

To evaluate the relationship between gout and age-related cataracts (ARCs).

Main findings:

In total, authors included 6 studies, of which three were cross-sectional and the other three were case-control studies. Authors attributed high quality to all six studies, where two studies were given a score of 7 and four studies a score of 8. Three of the included studies were conducted in Australia and three in America.

Based on the meta-analysis authors note that gout was significantly associated with increased odds of ARCs (odds ratio (OR) 1.53, 95% confidence interval (CI) 1.27±1.84). In the subgroup analysis, gout exhibited positive associations with the odds of posterior subcapsular cataracts (PSCs, OR 1.69, 95% CI: 1.06±2.70) and cortical cataracts (CCs, OR 1.39, 95% CI: 1.06±1.81). However, no association was identified between gout and the odds of nuclear cataracts. Authors did not identify significant heterogeneity (p=0.283, I2=16.9%). Sensitivity analysis did not alter the overall pooled results, in addition no significant publication bias was observed.

Authors note that findings from this review may help resolve inconsistencies in the relationship between gout and the odds of age-related cataract, however future research is needed to confirm these findings.

Methodology:

Inclusion criteria for this review consisted of: (1) original research papers directly reporting study results; and (2) cross-sectional or case-control studies estimating the influence of gout on cataract risk using odds ratios (ORs) or relative risks (RRs) and their corresponding 95% confidence intervals (CIs).

Authors conducted a search on Web of Science databases for studies published between 1991 and 2017. In addition, authors screened references of included studies as part of the search strategy.

Two reviewers independently screened for inclusion, extracted data and conducted quality assessment of included studies. The Newcastle-Ottawa Scale (NOS) was used for quality assessment. A maximum of nine stars can be assigned on this scale, which is organized as follows: four stars possible in the patient selection category, two stars possible in the comparability category, and three stars possible in the outcome assessment category. Scores of 7 or higher indicate good quality.

OR/RR values and their corresponding 95% CIs were extracted from all qualified studies and summarized to obtain pooled ORs/RRs. Subgroup analyses were conducted based on cataract subtype. The level of heterogeneity was evaluated using the Cochran’s Q statistic and I2 index score. In addition, authors conducted a sensitivity analysis, meta-regression and assessed publication bias using the Eggers’ linear regression test and Begg’s rank correlation test.

Applicability/external validity:

Authors note that most included studies in the meta-analysis were based in the general population, resulting in increased generalizability.

Geographic focus:

Authors included studies conducted in Australia and USA, therefore findings may only be applicable to the Caucasian population only.

Quality assessment:

Medium confidence was attributed in the conclusions about the effects of this study. Authors did not conduct a thorough search of the literature to ensure that all relevant studies were included in the review and restricted the inclusion of studies published between 1991 and 2017, implying the presence of publication bias within the review. This limitation, on the other hand, may impact of the reliability of the findings from this review. Authors used appropriate methods to screen studies for inclusion, extract data and assess the quality of included studies. Authors appropriately acknowledged the inclusion of cross-sectional and case-control studies in the meta-analysis as one the limitations of the review.