The aim of this study was to systematically evaluate the effects of femtosecond laser small incision lenticule extraction (SMILE) and posterior chamber phakic intraocular lens (ICL) implantation for the correction of high myopia.

A literature search was implemented in CNKI, Wanfang database, VIP database, PubMed, Embase and Cochrane Library. Two researchers independently performed literature search, screening, quality evaluation, and data extraction. Postoperative visual acuity, dry eye, safety, efficacy, and postoperative visual quality were analyzed. Postoperative uncorrected visual acuity, best corrected visual acuity, tear film break-up time, tear meniscus heigh, surgical efficiency and safety, contrast sensitivity and higher-order aberrations were all measured. Mean difference (MD) and its 95% confidence interval (CI) were used as statistical analysis variables.The heterogeneity among studies was tested by Q test and I² test. If P<0.05 or I²>50%, the heterogeneity was considered to be greater. Sensitivity analysis was used to eliminate studies with large publication bias differences or studies with high bias risk, and then the stability of the merger results was tested. If the heterogeneity was not significantly reduced after elimination, random effect model was performed; otherwise, fixed effect model was used.

In all databases, 59 literatures were retrieved. After excluding the repetitive 32 literatures, the literatures with in consistent contents or incomplete main outcome indicators and the literatures with data that cannot be extracted, there were 7 studies recruited for meta-analysis, including 439 eyes with SMILE and 422 eyes implanted with ICL. There was significant heterogeneity in postoperative best corrected visual acuity between them (I²=98%) and postoperative uncorrected visual acuity (I²=89%). After random effects model analysis, there was no statistically significant difference on postoperative best corrected visual acuity (MD=-0.02, 95%CI: -0.03 to 0.08, P>0.05). The postoperative uncorrected visual acuity as an outcome indicator suggested that the ICL group performed better than the SMILE group (MD=0.04, 95%CI: 0.00 to 0.07, P<0.05). There was non-significant heterogeneity between SMILE and ICL group in postoperative tear meniscus height and breakup time (I²=0) . After fixed effects model analysis, there were no statistically significant differences on the postoperative tear meniscus height and breakup time (MD=-0.00, -0.13, 95%CI: -0.03 to 0.02, -0.53 to 0.27; P>0.05). There was significant heterogeneity in safety and efficiency index between them (I²=92%, 73%). After random effects model analysis, there was no statistically significant difference on outcome indicator of safety and efficiency index(MD=-0.07, -0.03, 95%CI: -0.15 to 0.01, -0.08 to 0.01; P>0.05). For postoperative visual quality, most literatures showed that ICL group had lower high-order aberrations compared to SMILE group. However, it was shown that there were statistical differences in other indicators, such as modulation transfer function cut off (MTF cut off), objective scattering index (OSI), and contrast sensitivity (P<0.05). ICL implantation had a more significant effect on the improvement of contrast sensitivity in patients with high myopia.

ICL implantation shared the same safety and efficacy with SMILE on the correction of high myopia. Postoperative dry eye complications can be improved in a short period of time. ICL implantation has a more ideal effect than SMILE on the correction of uncorrected visual acuity and a more obvious effect on the improvement of visual quality.