Intrastromal Corneal Ring Segment Implantation in 409 Paracentral Keratoconic Eyes

To assess the efficacy outcomes of implanting intrastromal corneal ring segments (ICRS) to correct paracentral keratoconus.

Four hundred nine eyes with paracentral keratoconus, in which the differences between the axes of refractive cylinder and the corneal flattest meridian and the comatic aberration map were less than 30 degrees, were evaluated before and after the implantation of Ferrara-type ICRS. Snellen uncorrected and best-corrected distance visual acuity, residual refractive errors analyzed with vector analysis, and the root mean square for corneal coma-like aberration for a pupil size of 4.5 mm were recorded before and 6 months after ICRS implantation.

The mean uncorrected distance visual acuity (Snellen decimal scale) rose from 0.19 ± 0.19 before ICRS implantation to 0.42 ± 0.30 after implantation (P < 0.0001). The mean preoperative best-corrected distance visual acuity was 0.69 ± 0.24 and the postoperative value was 0.77 ± 0.23 (P < 0.0001). The safety index was 1.13. The spherical equivalent declined steeply after ICRS implantation (P < 0.0001). Cylinder power decreased by more than 50% in 71% of the eyes. The root mean square for corneal coma-like aberration for a 4.5-mm pupil changed from 1.32 ± 1.01 μm before surgery to 1.06 ± 0.85 μm after surgery (P ≤ 0.001).

The Ferrara-type ICRS implantation is a safe and effective procedure for treating patients with keratoconus that meets the morphological characteristics of the sample under study.