A randomized controlled trial of symmetric versus asymmetric intrastromal corneal ring segments for asymmetric keratoconus

Purpose This study evaluated the safety and effectiveness of two models of intrastromal corneal ring segments (ICRS)—symmetric (uniform thickness and base width) and asymmetric (progressive thickness and base width)—for the treatment of oval phenotype keratoconus. Methods A prospective, randomized, controlled clinical study was conducted on 64 eyes from 47 patients, divided into two groups: Group 1 (33 eyes) received symmetric ICRS, and Group 2 (31 eyes) received asymmetric ICRS. Comprehensive ophthalmic evaluations, including visual acuity, corneal topography, tomography, and aberrometry, were performed preoperatively and at 1, 3, 6, and 12 months postoperatively. Results At 12 months, Group 2 demonstrated significantly greater reductions in K1, Km, Kmax, asphericity, vertical coma and spherical aberration, and most topographic indices compared to Group 1. Best-corrected visual acuity was higher in Group 2, reaching statistical significance at 6 months. No implant-related complications were observed in either group. Conclusions Asymmetric ICRS provided superior topographic, tomographic, and aberrometric outcomes compared to symmetric ICRS in the treatment of asymmetric keratoconus, leading to greater improvements in corneal regularity, asphericity, and cone inclination. Clinical Trial Registration: This study was registered with the National Research Ethics Commission (CONEP) under registration number 32212020.9.0000.5505.