Asymmetric Intracorneal Ring Segments for the Management of Keratoconus: A Systematic Review and Meta-Analysis

To investigate the outcomes of asymmetric (AS) Keraring intracorneal ring segments (ICRS) implantation in patients with all types, types 2 (Duck) and 3 (Snowman) of keratoconus.

The protocol for this systematic review was registered in the International Prospective Register of Systematic Reviews (CRD42023482841). From inception to December 2023, we systematically searched PubMed, Embase, Cochrane Library, and Web of Science. Due to heterogeneity, a random-effects model was used for all analyses. Publication bias was evaluated using the risk of bias in nonrandomized studies of interventions tool, and sensitivity analyses included leave-one-out and Baujat methods. Meta-regression explored the effects of age, sex, and follow-up time on heterogeneous outcomes. Software R version 4.3.2 was used for statistical analysis.

From 318 initial articles, 7 studies (3 prospective and 4 retrospective cohorts) met inclusion criteria, pooling 435 eyes from 365 patients across seven countries. Significant improvements were observed postoperatively for uncorrected distance visual acuity (mean differences [MD]: 0.49, confidence interval [CI]: 0.42-0.57), corrected distance visual acuity (CDVA) (MD: 0.18, CI: 0.07-0.29), topographic astigmatism (MD: 2.04 diopter [D], CI: 1.51-2.58 D), maximum keratometric (MD: 4.42 D, CI: 3.24-5.60 D), comatic aberration (MD: 0.56 µm, CI: 0.29-0.82 µm), refractive astigmatism (MD: -2.52 D, CI: -3.08 to -1.95 D), spherical equivalent (SE) (MD: -2.86 D, CI: -4.02 to -1.70 D), and mean keratometry (MD: 2.92 D, CI: 1.94-3.91 D). Subgroup analyses for keratoconus types 2 and 3 revealed consistent improvements across most parameters. Sensitivity analysis identified specific studies influencing heterogeneity without altering statistical significance. Meta-regression revealed associations for follow-up and male gender in SE, CDVA, and topographic astigmatism, while age showed no consistent effect.

The implantation of AS Keraring ICRS was safe and effective, improving visual, topographic, and refractive parameters in patients with keratoconus of phenotype types 2, 3, and all types.