Effect of clonidine on intraocular pressure following cataract surgery: a systematic review and meta-analysis

Methodological quality of the review: High quality

Author: Hu A, Wu S and Long Y

Region: Not reported

Sector: Cataract surgery

Sub-sector: Intraocular pressure

Type of cataract: Age-related cataract

Equity focus: None

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Clonidine was found to make the eye surgery easy and reduce complications (for example expulsion of the vitreous humor) by decreasing intraocular pressure. In addition, previous studies reported that clonidine could produce sedation without inducing hypnosis, and decrease postoperative pain, blood pressure and heart rate. Previous studies reported that clonidine could significantly reduce intraocular pressure and promote sedation in patients undergoing cataract surgery. However, results remained controversial.

Objectives:

To evaluate the effect of clonidine intervention after cataract surgery.

Main findings:

In total, authors included a total of four randomized control trials (RCTs) involving 210 patients in the meta-analysis. Overall, authors noted that compared with control intervention, clonidine intervention was found to significantly reduce intraocular pressure (Standardized mean difference (SMD)=-0.84; 95% confidence interval (CI)=-1.18 to -0.49; P<0.00001) and improve Ramsay Scale (SMD =1.44; 95% CI=0.12 to 2.77; P=0.03), but showed no impact on heart rate (SMD=-0.38; 95% CI=-0.82 to 0.77; P=0.09) and arrhythmia (relative risk (RR)=0.32; 95% CI=0.03 to 3.84; P=0.37). Authors did not observed heterogeneity among included studies. Overall, included RCTs were of high quality, where two were attributed a score of 3, and one was given a score of 4 and one study was attributed a score of 5.

Based on the authors’ analysis, authors concluded that compared to control intervention, clonidine intervention was found to significantly reduce intraocular pressure and improve sedation, but showed no influence on heart rate and arrhythmia in patients undergoing cataract surgery.

Methodology: 

Authors reported that this systematic review and meta-analysis were conducted according to the guidance of the Preferred Reporting Items for Systematic Review and Meta-analysis statement and the Cochrane Handbook for Systematic Reviews of Interventions.

The inclusion criteria were as follows: (1) patients underwent cataract surgery; (2) Treatment intervention was clonidine versus placebo; and (3) study design was RCT. PubMed, Embase, Web of science, EBSCO, and the Cochrane library were systematically searched from inception to April 2017.

Two reviewers independently screened studies for inclusion, extracted data and assessed the methodological quality of included studies. The primary outcome was intraocular pressure. Secondary outcomes included Ramsay Scale, heart rate, arrhythmia. The Jadad Scale was used to evaluate the methodological quality of each RCT included in this meta-analysis.

Standardized Mean differences (SMDs) with 95% confidence intervals (CIs) for continuous outcomes (intraocular pressure, Ramsay Scale, heart rate), and risk ratios (RRs) with 95% CIs for dichotomous outcomes (arrhythmia) were used to estimate the pooled effects. All meta-analyses were performed using random-effects models with DerSimonian and Laird weights. Heterogeneity was tested using the Cochran Q statistic (P<0.1) and quantified with the I2 statistic, which described the variation of effect size that was attributable to heterogeneity across studies.

Applicability/external validity:

Authors note that their analysis was based on four RCTs, but all of them had a relatively small sample size (n<100). Overestimation of the treatment effect was more likely in smaller trials compared with larger samples.

Geographic focus:

Authors do not report the geographical focus of included studies.

Summary of quality assessment:

High confidence was attributed in the conclusions about the effects of this review. authors used appropriate methods to screen, extract data and assess methodological quality of included studies. Authors ensured that included studies were similar enough to pool the data.