# Corneal Allogeneic Intrastromal Ring Segments for Treating Keratoconus—Systematic Review and Meta-Analysis

## TL;DR

This study reviews and analyzes the effectiveness of corneal implants for treating keratoconus, finding consistent improvements in vision and corneal shape.

## Contribution

A systematic review and meta-analysis evaluating the effectiveness of different CAIRS techniques and cross-linking for keratoconus.

## Key findings

- CAIRS implantation significantly improved uncorrected and best corrected visual acuity at one month and one year post-surgery.
- Keratometry values decreased significantly after CAIRS implantation, with sustained improvements over one year.
- No significant differences in outcomes were found between different surgical techniques or the use of corneal cross-linking.

## Abstract

Background and Objectives: Corneal allogeneic intrastromal ring segments (CAIRS) are designed to decrease and stabilize the extent of corneal ectasia in keratoconus patients. This systematic review and meta-analysis evaluate the effectiveness of different surgical techniques for CAIRS preparation and the adjunctive use of corneal cross-linking. Materials and Methods: Following the PRISMA statement and checklist, a comprehensive search was conducted in Embase, Medline, and the Cochrane Controlled Trials Register, through the use of a systematic search approach in accordance with the Cochrane Collaboration guidelines. Results: Eighteen studies, involving 567 eyes of 459 patients, met the inclusion criteria. At one month postoperatively, CAIRS implantation significantly improved uncorrected visual acuity (UCVA) (−0.45 logMAR, 95% CI [−0.59 to −0.31], p < 0.001) and best corrected visual acuity (BCVA) (−0.36 logMAR, 95% CI [−0.46 to −0.25], p < 0.001). These improvements remained significant after one year (UCVA: −0.39 logMAR, 95% CI [−0.48 to −0.30], p < 0.001; BCVA: −0.34 logMAR, 95% CI [−0.50 to −0.18], p < 0.001). Similarly, mean simulated keratometry (Kmean) decreased by −4.42 D (95% CI [−5.94 to −2.90], p < 0.001) and maximum keratometry (Kmax) by −3.88 D (95% CI [−6.71 to −1.05], p < 0.001) at one month, with sustained reductions at one year (−3.59 D, 95% CI [−4.35 to −2.84], p < 0.001 and −3.73 D, 95% CI [−4.91 to −2.55], p < 0.001). No significant differences in surgical outcome have been observed between the different surgical techniques. Conclusions: CAIRS implantation appears to be an effective treatment option for keratoconus, regardless of the technique used for segment preparation or the addition of corneal cross-linking. No approach demonstrated clear clinical superiority over others in the first year after surgery.