Femtosecond Laser Created Corneal Allogenic Intrastromal Ring Segments for Keratoconus

BACKGROUND: To evaluate the clinical outcomes of femtosecond laser-created corneal allogenic intrastromal ring segments (femto-CAIRS) in keratoconic eyes using a newly described nomogram. METHODS: This retrospective case series recruited 85 eyes from 75 patients. Corrected and uncorrected visual acuity (CDVA/UDVA), refractive error, corneal topography, and higher-order aberrations were measured prior to surgery and ≥ 3 months postoperatively. All CAIRS were created using a femtosecond laser and the Brisbane nomogram was used to determine segment width, thickness, arc length, implantation axis and channel depth based on individual corneal topography. RESULTS: The mean follow-up time was 7.5 ± 5.0 months; 18 eyes had prior cross-linking (CXL), 30 underwent simultaneous CXL, and 37 had no CXL. Postoperatively, UDVA improved by 0.4 logMAR (p < 0.001) and CDVA by 0.2 logMAR (p < 0.001). There was an improvement of 5 or more lines in 31 eyes (43.7%), 8 eyes (11.3%) had no change in UDVA, 1 eye lost 1 line, and 1 eye lost 2 lines. There was a significant reduction in the mean spherical equivalent, refractive astigmatism, flat K, steep K, mean K, and KMax, and an improvement in total higher order aberrations and vertical coma (all p < 0.001). Reduction in KMax was greater in eyes that underwent simultaneous CXL compared to those without CXL (-4.28D vs. -0.70D; p = 0.018). No significant complications occurred. CONCLUSIONS: Femto-CAIRS guided by the Brisbane nomogram provides a tailored treatment approach that improved visual acuity and regularisation of the central cornea. Further studies are required to validate our nomogram and clarify the effect of cross-linking on CAIRS.