Elevation Changes of Central Posterior Corneal Surface After Intracorneal Ring Segment Implantation in Keratoconus

Purpose: To compare changes that occur at the posterior corneal surface after the implantation of intracorneal ring segments (ICRSs) using either mechanical or femtosecond laser-assisted procedures and to correlate these changes with the visual outcome achieved. Methods: Retrospective, nonrandomized, and interventional case series including 223 consecutive eyes of 186 patients with keratoconus ranging in age from 16 to 39 years that were implanted with ring segments (KeraRing; Mediphacos) at Kartal Training and Research Hospital, Istanbul, Turkey. Two groups were created according to the surgical technique used: mechanical group (168 eyes) and femtosecond group (55 eyes). Visual and refractive outcomes and corneal elevation changes were evaluated during a 24-month follow-up. Correlations between visual and posterior elevation changes were evaluated. Results: The posterior corneal surface could not be analyzed with accuracy for diameters larger than the diameter of the ICRS implant. A statistically significant reduction of maximum elevation for both the corneal surfaces was observed at 1 month after the surgery (P < 0.01), with additional reductions at 3 and 6 months (P <= 0.03). In addition, the posterior best-fit sphere was flattened significantly at 1 month after the surgery in both the groups, with additional flattening at 3 months (P <= 0.03). No significant differences between groups in posterior corneal elevation parameters were found at any time point of the follow-up (P >= 0.14). Moderate and significant correlations of the postoperative visual outcome with the change in posterior best-fit sphere were found only in the femtosecond group. Conclusions: A central corneal flattening of the posterior corneal surface occurs after ring segment implantation in keratoconus.