Corneal allogenic intrastromal ring segments improve visual and topographic outcomes in advanced keratoconus

This study aims to evaluate the efficacy and safety of corneal allogeneic intrastromal ring segments (CAIRS) in patients with advanced keratoconus. This retrospective observational study included 25 eyes of 20 patients with advanced keratoconus (defined as a maximum keratometry (Kmax) of ≥ 58.0 D) who had unsatisfactory vision with spectacles and intolerance to scleral lenses. All patients underwent femtosecond laser-assisted tunnel creation, followed by implantation of allogeneic stromal segments prepared from donor corneal tissue. In cases of suboptimal outcomes, tissue reshaping or double segment implantation was performed. Pre- and postoperative evaluations included uncorrected (UDVA) and corrected distance visual acuity (CDVA), manifest refraction, spherical equivalent (SE), Scheimpflug-based tomography, keratometric parameters, corneal thickness, and higher-order aberrations. Patients were followed for a mean of 11 months. Mean UDVA improved significantly from 1.42 ± 0.33 LogMAR to 0.46 ± 0.27 LogMAR (p < 0.001), and CDVA improved from 1.18 ± 0.44 LogMAR to 0.25 ± 0.16 LogMAR (p < 0.001), with nearly half of the patients gaining 10 Snellen lines. Mean SE decreased from - 9.66 D to - 1.33 D (p < 0.001). Significant reductions in K1, K2, Kmean, and Kmax were observed (all p < 0.05), with coma aberration improving from 1.39 μm to 0.41 μm (p = 0.005). Central corneal thickness remained stable. No adverse events occurred. In conclusion, CAIRS provided substantial visual, refractive, and topographic improvements in advanced keratoconus, including very severe cases. Larger, prospective, long-term studies are warranted to confirm its role in advanced keratoconus management.