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.