Corneal Allogeneic Intrastromal Ring Segments for keratoconus – recent evidence and the move to customized and custom shaped CAIRS

PURPOSE OF REVIEW: This review focuses on the use in patients with keratoconus, of corneal allogeneic intrastromal ring segments (CAIRS) as well as customized and custom shaped CAIRS for corneal reshaping, stabilization and individualized, tissue-based corneal contouring, while delaying or avoiding keratoplasty. RECENT FINDINGS: CAIRS is being widely used in advanced cases of keratoconus, as biological replacement for synthetic intra-corneal ring segments and to prevent the need for keratoplasty. It is also being adopted in early disease in combination with corneal cross-linking. Various techniques and modifications are described as well as its use in different situations. Femtosecond and double bladed trephined CAIRS are discussed, including recent unpublished data demonstrating comparable dimensional accuracy with both. Double bladed trephines may also offer potential for greater segment thickness and customization. SUMMARY: CAIRS is evolving into a customizable corneal contouring approach that may complement and potentially reduce reliance on, existing treatment modalities. When combined with corneal cross-linking, it offers both biomechanical stabilization and visual rehabilitation. Future advances are likely to center on data-driven personalization tailored to each patient's corneal phenotype and visual needs, an approach that becomes increasingly important as CAIRS use expands in keratoconus.