Methodological quality of the review: Low confidence

Author: Xiao K, Dong Y, Xiao X, Liang S, Wang J, Qian C, Wan G.

Region: United States of America (USA), Taiwan and Korea

Sector: Biomedical

Subsector: Treatment

Equity focus: Not stated

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:
Pars plana vitrectomy (PPV) is considered to be an essential and effective surgical approach for the management of complications of diabetic retinopathy. Given the high rate of accelerated cataract progression after PPV, PPV combined with cataract surgery appears to be an attractive treatment option for patients with diabetes. However, this combined surgical approach remains controversial in terms of effectiveness and safety.

Objectives:
Evaluate the treatment outcome of PPV, with or without cataract surgery.

Main findings:
A total of five studies were included in the meta-analysis. One study was conducted in Taiwan, two in Korea and two in the USA. Of these, one was an RCT, one was a prospective study, and three were retrospective studies. A total of 325 and 422 eyes underwent PPV alone and PPV combined with cataract surgery, respectively.

In four of the included studies, final visual acuity did not vary significantly between patients undergoing PPV alone and those undergoing PPV combined with cataract surgery (combined surgery). Only one study reported better visual improvement in the combined treatment group. Our analysis also showed that most phakic eyes after PPV had cataract progression with varying degrees. In addition, patients receiving PPV alone had a lower risk of neovascular glaucoma (OR 0.36; P<0.05), iris synechias to anterior capsule (OR 0.36; P<0.05), and iris rubeosis (OR 0.26; P<0.05) compared with those receiving combined surgery.

Authors conclude that overall, their meta-analysis shows that PPV combined with cataract surgery achieved good outcomes without a substantial increased risk to visual acuity or most complications. Authors note that given the high rates of cataract progression after PPV, combined surgery may be the more appropriate treatment for patients with diabetes and coexistent visually significant cataract. Large randomised and prospective studies are required to refine this review’s conclusions and evaluate the long-term effect of the PPV combined with cataract surgery approach in patients with diabetes.

Methodology:
Authors conducted a systematic search of the websites PubMed, Web of Science, and the Cochrane Library to identify relevant available articles published up to April 2019. The language was restricted to English. In addition, authors reviewed reference lists from retrieved articles in an attempt to identify other potentially relevant studies.

The inclusion criteria were: (1) randomised controlled trials (RCTs) or high-quality comparative studies; (2) studies that compared the therapeutic effects of PPV alone versus PPV combined with cataract surgery in patients with diabetes; and (3) all studies that contained adequate informative data, such as postoperative complications and final visual acuity.

Data extraction of included studies was conducted by two reviewers independently and quality assessment for randomised controlled trials was conducted using the Cochrane Collaboration tool; for retrospective studies, authors used the modified Newcastle-Ottawa Scale.

Statistical analyses were performed using the Cochrane Review Manager software. An odds ratio (OR) with corresponding 95% confidence interval (CI) was used to evaluate the incidence of postoperative complications in a random effects model, and P<0.05 was considered to be statistically significant. The between-study heterogeneity was tested using the Chi-square test and the I² statistic. Sensitivity analyses were also conducted.

Applicability/external validity:
Authors note that given the high rates of cataract progression after PPV, combined surgery may be the more appropriate treatment for patients with diabetes and coexistent visually significant cataract. In addition, the authors highlighted some limitations which need to be considered when interpreting the results: some studies included in the meta-analysis were quite dated, and the relatively old-fashioned surgical methods and strategies reported in these studies may have increased the risk of postoperative complications. The results evaluating NVG and VH showed large heterogeneity.

Geographic focus:
Authors did not discuss the applicability of findings to low and middle income countries.

Summary of quality assessment:
Although authors used appropriate methods to analyse findings of included studies, authors did not conduct thorough searches of the literature to ensure that all relevant studies were included in the review. In addition, rigorous methods were not used in the process of study selection, increasing the risk of publication bias. The level of bias of included studies is not clear, which can ultimately impact on study findings and validity. Therefore, low confidence was attributed to the conclusions about the effects of this study.