Polymethylmethacrylate and Corneal Allogenic Intrastromal Ring Segments: Same Cornea, Different Optical Zones

Purpose: To present the first report of corneal allogenic intrastromal ring segment (CAIRS) insertion in a cornea with an existing polymethylmethacrylate (PMMA) segment each at a different optical zone. Methods: A 29-year-old man with severe keratoconus treated with PMMA ring segment implantation at a 7-mm optical zone and 375-µm depth presented with moderate improvement in visual acuity and topography. An allogenic segment was implanted at a depth of 260 µm and an optical zone of 5 mm without explantation of the existing segment. Results: There was additional topographic regularization and significant corneal flattening, with improvement in corrected distance visual acuity from 20/60 following PMMA insertion to 20/30 following CAIRS insertion. Corneal topography showed improvement in corneal regularity with centration of the cone on the corneal vertex and improvement in coma (from 1.69 diopters [D] @ 75° to 0.51 D @ 56° at 6-mm optical zone) and keratometric cylinder (from −6.47 D × 35° to −3.59 D × 18°). Conclusions: The implantation of CAIRS in an eye that has previously undergone synthetic segment implantation at a different optical zone was demonstrated to be a promising method for regularizing topography and improving vision in this case. [ Journal of Refractive Surgery Case Reports. 2023;3(3):e38–e41.]