Implantable collamer lens versus small incision lenticule extraction for high myopia correction: A systematic review and meta-analysis

Authors: Cao K, Zhang J, Wang J, Yusufu M, Jin S, Chen S, Wang N, Jin Z and Wan XH.

Geographical coverage: Not reported

Sector: Biomedical

Sub-sector: Treatment of myopia

Equity focus: Adults

Study population: General population aged 18 years old or older.

Review type: Other review

Quantitative synthesis method: Narrative review and meta-analysis

Qualitative synthesis method: Not applicable

Background:

Small incision lenticule extraction (SMILE) is a well-established method for correcting low-to-moderate myopia. While it has shown promising results for high myopia, it has inherent limitations such as thin ablation depths, ablation zones, and increased aberrations, which can lead to dry eye, myopic regression, haze, and corneal ectasia. Implantable collamer lens (ICL) implantation is another promising method for high myopia correction, with predictable and stable postoperative spherical equivalent error (SER). ICL implantation expands the target population to include patients with thin corneas and even keratoconus.

Objectives: To compare the efficacy, safety, predictability and visual quality between ICL implantation and SMILE for high myopia correction in adults.

Main findings:

This review includes a total of five observational studies in the meta-analysis. All subjects in the studies included high myopic adults (age≥18), the sample sizes (number of eyes) ranged from 76 to 197. Subjects’ refraction ranged from -6D to -12D. Three studies used EVO Visian ICL (Visian ICL V4c) and two studies used Visian ICL without knowing the model. The median follow-up duration of five studies ranged from three months to 60 months. The geographic locations of studies were not reported by the authors.

Based on the pooled analysis, authors reported that ICL implementation showed a statistically better index (MD=0.09, 95%CI:0.01 to 0.16) and a better safety index (MD=0.08, 95%CI: 0.00, 0.16) than SMILE. However high heterogeneity was identified among these studies (I² > 50%).

This review shows that when compared with SMILE-treated eyes, more ICL-treated eyes gained one or more lines of CVDA (RR = 1.54, 95%CI:1.28 to 1.86), more ICL-treated eyes gained two or more lines of CDVA (RR = 2.09, 95%CI:1.40 to 3.13), less ICL-treated eyes lost one or more lines of CDVA (RR = 0.17, 95%CI: 0.05 to 0.63). No eyes lost two or more Snellen lines in each group.

Authors found no statistical difference in predictability of within ±0.5D between two treatments (RR = 1.13, 95%CI: 0.94 to 1.36), there was no statistical difference in predictability of within ±1D either (RR = 1.00, 95%CI:0.98 to 1.02). Based on the data analysis, authors found a smaller increase of total HOAs for ICL-treated eyes compared to SMILE-treated eyes (MD = -0.23, 95%CI: -0.42, -0.03). Due to limited data, authors reported not being able to pool MD or RR for the following outcomes: cornea endothelial cell loss, complications including cataract and dry eye, visual quality including objective scatter index (OSI) and modulation transfer function cut-off frequency (MTF cut-off) value.

Authors found no presence of publication bias based on Egger’s test (p >0.05).

Methodology:

The inclusion criteria for studies to be included in this review were: 1) subjects with high myopia (SER should be equal or greater than 6 dioptre, D); 2) subjects aged equal or over 18 years old; and 3) the intervention measures must include ICL implantation and SMILE.

Authors conducted a search on the following databases PubMed, Science Direct and the Cochrane Central Register of Controlled Trials from inception to August 2021 for studies published in English.

The following outcomes were quantitatively assessed by the authors: the efficacy index, safety index, changes in Snellen lines of CDVA, predictability, incidence of halos, and change in HOAs. Besides, the following outcomes were qualitatively described: endothelial cell loss, complications including cataract and dry eye, visual quality including objective scatter index (OSI) and modulation transfer function cut-off frequency value.

Authors extracted reference data of included studies, sample size, study design, mean follow-up duration, subjects’ SER range and type of ICL. Outcome data extracted included number of halos and number of events.

To analyse data, authors pooled data into a meta-analysis using either a fixed- or random-effects model depending on heterogeneity across included studies. Heterogeneity was assessed by a Q-test and the I² statistic. Authors used the mean differences (MDs) and 95% confidence intervals (CIs) to make comparison of continuous outcomes between ICL implantation and SMILE; they used risk ratios (RRs) and 95% CIs to estimate categorical outcomes. Egger’s test was performed to determine publication bias. The significance level was set to be 0.05, two-tailed.

Applicability/external validity:

Authors note that, for high myopia correction, ICL implantation might be a better choice than SMILE. However, the conclusion came from observational studies with relatively short-term follow-up.

Geographic focus: Authors did not report the geographic regions of included studies.

Summary of quality assessment:

Important limitations were identified in the review. When reporting the inclusion criteria, authors do not report the type of studies and outcomes which studies should report to be eligible for inclusion in the review. Searches were not comprehensive enough to ensure that all relevant studies were identified. It is not clear from the review if authors used rigorous methods to screen studies for inclusion and extract data of included studies. Furthermore, authors did not assess the methodological quality of studies. Therefore, due to these limitations, we attributed a low confidence in the conclusions about the effects of this study.