The protective effect of ophthalmic viscoelastic devices on endothelial cell loss during cataract surgery: a meta-analysis using mixed treatment comparisons

Methodological quality of the review: Low confidence

Author: Van den Bruel A, Gailly J, Devriese S, Welton NJ, Shortt AJ, Vrijens F.

Region: Details not provided

Sector: Ophthalmic viscoelastic devices, endothelial cell loss and cataract surgery.

Sub-sector: Viscoadaptives, super viscosity cohesives, viscous cohesives, medium viscosity dispersives, very low viscosity dispersives.

Type of cataract: Age-related cataract

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis methods: Not applicable

Background

Any direct trauma to the corneal endothelium results in a decrease in the number of cells of the lining. When cell density falls below 500-1000 cells/mm², the cornea becomes ‘oedematous and assumes the clinical appearance of bullous keratopathy, a serious complication that may occur following cataract surgery in up to 0.3% of patients’.  Due to the link between surgical trauma and endothelial cell loss, surgeons use protective ophthalmic viscosurgical devices (OVDs) to minimize cell loss. To date, there is little data to support the use of one type of OVD over another in terms of minimizing endothelial cell loss following cataract surgery.

Research objectives

‘To compare ophthalmic viscoelastic devices (OVDs) in protecting the cornea from endothelial cell loss during cataract surgery’.

Main findings

The review included 21 randomized controlled trials evaluating the effect of OVDs on endothelial cell density in patients undergoing cataract surgery.

Direct comparison meta-analysis indicated that viscoadaptives led to a lower loss of cell density, with one study finding a lower loss of cell density of 198 (95% CI 99 to 298) cells/mm², and three studies finding a lower cell loss of 112 (95% CI 14 to 211) cells/mm², compared with super viscous cohesives. Compared with other OVDs, no significant differences were identified. The soft shell technique showed a statistically significant lower loss compared with viscous cohesives, of 36 (95% CI 3 to 69) cells/mm².

Mixed treatment comparisons indicate that viscoadaptives had an 80% chance to be the best treatment, followed by soft shell technique at 18%. Differences between each treatment option analysed were very small, with <100 cells/mm² between various OVDs in endothelial cell density loss three months after cataract surgery.

Overall, authors concluded that viscoadaptives were potentially superior to other OVD types, with other treatments never coming out as the best strategy. Absolute differences between the OVDs analysed in loss in endothelial cell density were <100 cells/mm², meaning that differences may not be clinically relevant in most patients. Authors suggested that a cost-effectiveness analysis of OVD treatment options needed to be addressed in future research.

Methodology

The authors included randomized controlled trials evaluating the effect of OVDs on endothelial cell density in patients undergoing cataract surgery. The outcome measure for the review was loss in endothelial cell density three months after surgery.

Authors searched MEDLINE and EMBASE from inception up until 2007. Studies were excluded if they were not written in English, French, German or Dutch. Selected studies were critically appraised using an extended version of the Jadad scale, subsequently, data were extracted in duplicate. Authors did not report if two reviewers conducted the study selection, data extraction and quality assessment of included studies.

Authors conducted a meta-analysis of direct comparisons as well as a mixed treatment comparison (MTC) analysis, which combined all effects from direct and indirect comparisons to obtain estimates for all comparisons. A difference of more than 100 cells/mm² was considered a clinically relevant difference.

Applicability/external validity

Authors did not directly discuss the applicability or external validity of the review findings.

Geographic focus

Authors did not provide geographical location of included studies.

Quality assessment

This review was attributed low confidence in the conclusions about the effects of this review as important limitations were identified. The authors, although covering relevant databases in the literature search, did not conduct a search of reference lists of included trials, did not contact experts for potentially relevant studies and restricted the search to published articles. It was not clear if this study covers an appropriate period of time as it was published in 2011 and searches were conducted from the beginning of the databases up until 2007. Additionally, authors did not report if article screening for inclusion in the review and data extraction of included studies were conducted by two reviewers independently. Nevertheless, the methods used to analyse the studies were clear and the quality and risk of bias for each individual study included in the review was reported. Meta-analysis seemed appropriate given the similarity in study design and outcomes of the included studies.