Predictability Of Double-Asymmetric Pmma Intrastromal Ring Segments In Keratoconus

To assess the 12-month refractive, tomographic, and pachymetric predictability of double-asymmetric PMMA intrastromal ring segments in keratoconus treated with simultaneous accelerated corneal cross-linking.

Cornea & Ocular surface Department, Zaldivar Institute, Mendoza, Argentina

Retrospective study of keratoconus eyes undergoing femtosecond laser–assisted implantation of double-asymmetric PMMA intrastromal ring segments (160° arc, 250 µm thickness, 6 mm optical zone) combined with simultaneous accelerated corneal cross-linking. Selection followed Alfonso’s classification, including duck-type phenotypes with ≥30° disparity between comatic, topographic, and refractive axes. Tunnels were created with femtosecond laser, with depth and centration individualized according to corneal thickness and tomographic features. Outcomes at 12 months included CDVA, cylinder, Km, K2, and pachymetry. Predictability was assessed by the consistency of K2 reduction and coma improvement across cases. Safety was recorded

Twenty-four eyes completed 12-month follow-up. Mean keratometry decreased from 46.97 D to 45.95 D (−1.12 D), with a steeper meridian reduction of −1.99 D in K2. Visual acuity improved in parallel with refractive stabilization. Coma decreased significantly from 1.62 ± 0.81 µm to 0.99 ± 0.59 µm (p < 0.001). Improvement in visual performance was supported by postoperative visual quality analysis. Pachymetric values remained stable without evidence of progressive thinning. No intra- or postoperative complications or segment explantations were observed.

Double-asymmetric PMMA intrastromal ring segments combined with accelerated corneal cross-linking produced consistent steep keratometry reduction and significant coma improvement, with stable pachymetric profiles at 12 months. These findings demonstrate reproducible refractive and tomographic outcomes in selected asymmetric keratoconus phenotypes.