Long-Term Outcomes of Progressive Thickness Intrastromal Corneal Ring Segments for Keratoconic Eyes: A 4-Year Follow-Up.

PURPOSE: To evaluate the long-term visual, refractive, and tomographic outcomes of progressive thickness intrastromal corneal ring segment implantation using the KeraRing AS in patients with keratoconus (KC).

METHODS

In this historical cohort study, 36 eyes from 36 patients with progressive KC underwent femtosecond-assisted KeraRing AS (Mediphaco, Brazil) implantation. Preoperative and postoperative uncorrected and corrected distance visual acuity, spherical equivalent (SE), astigmatism, keratometric indices, and pachymetric parameters were analyzed at 1- and 4-year follow-ups.

RESULTS

Uncorrected distance visual acuity improved from 0.71 ± 0.36 to 0.34 ± 0.27 logarithm of the Minimum Angle of Resolution (logMAR) at 1 year and 0.28 ± 0.26 logMAR at 4 years (P <0.001). Corrected distance visual acuity improved from 0.33 ± 0.20 to 0.22 ± 0.16 logMAR at 1 year and 0.16 ± 0.13 logMAR at 4 years (P <0.001). SE improved from -5.38 ± 3.03 diopters (D) to -1.00 ± 1.48 D at 1 year but showed partial recurrence to -1.68 ± 1.83 D at 4 years (P = 0.011). Mean keratometry decreased from 46.52 ± 2.41 D to 43.82 ± 2.40 D at 1 year and increased significantly to 44.94 ± 2.18 D at 4 years (P <0.001). Corneal thickness parameters remained stable throughout the follow-up period.

CONCLUSIONS

KeraRing AS implantation provides significant initial improvements in visual and topographic parameters in progressive KC. However, notable regression occurs after 1 year, with significant increases in spherical power, SE, and all keratometric parameters between 1 and 4 years. This regression pattern emphasizes the importance of long-term monitoring and potential need for additional interventions.