Biology Or Mechanics? Real-World Outcomes Of Allogenic Versus Synthetic Intrastromal Ring Segments In Keratoconus

To compare the clinical performance, tomographic behavior, and refractive stability of corneal allogenic intrastromal ring segments (CAIRS) versus synthetic intracorneal ring segments (ICRS) in keratoconus, and to assess how biologic versus mechanical intrastromal strategies influence long-term outcomes, and to evaluate whether a biologic, tissue-additive approach offers advantages over conventional mechanical corneal reshaping in real-world practicein.

Hazem Yassin International Cornea Center

A retrospective comparative analysis was conducted on 38 keratoconic eyes treated with either CAIRS or ICRS as part of routine tertiary corneal care. Pre- and postoperative assessments included autorefractometry, Pentacam-derived keratometry (K1, K2), and thinnest corneal pachymetry. Longitudinal follow-up focused on corneal regularization, refractive behavior, pachymetric stability, and safety profile. Surgical planning and segment selection were guided by phenotype-based keratoconus nomograms widely applied in regional practice and aligned with international consensus guidelines.

CAIRS and ICRS achieved clinically meaningful corneal regularization. ICRS-treated eyes showed more pronounced early keratometric flattening, with K2 reductions reaching 4–5 diopters and significant early reduction in refractive cylinder, particularly in thicker corneas with well-centered cones. However, greater refractive variability and late functional instability occurred in a subset of ICRS-treated eyes, despite relatively stable tomographic parameters.In contrast,CAIRS-treated eyes exhibited more gradual but consistent improvement in corneal shape, typically achieving 2–4 diopters of K2 reduction,With superior long-term refractive and tomographic stability,especially in borderline pachymetry,decentered cones,and advanced ectasia overal

Intrastromal ring surgery remains an effective corneal regularization strategy in keratoconus when applied using appropriate, nomogram-guided patient selection. Synthetic ICRS provides powerful early corneal flattening in carefully selected, anatomically favorable eyes, whereas CAIRS offers a more physiologic, tissue-preserving biomechanical response with superior long-term stability, particularly in thinner and more complex keratoconic corneas. These findings emphasize the importance of phenotype-driven decision-making and support the integration of biologic intrastromal techniques as a valuable component of contemporary keratoconus management.