Femtosecond laser implantation of a 340-degree intrastromal corneal ring segment in keratoconus: Short-term outcomes

Purpose To evaluate the short-term outcomes of femtosecond laser–assisted implantation of a 340-degree intracorneal ring (ICR) (Keraring) in patients with keratoconus. Setting Four centers in Iran. Design Prospective case series. Methods All cases had implantation of the 340-degree ICR after tunnel creation with a femtosecond laser. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, sphere, cylinder, manifest refraction spherical equivalent (MRSE), mean keratometry (K), steep K, and flat K were evaluated preoperatively and 1, 3, and 6 months postoperatively. Results Eighteen eyes of 17 patients were included. The mean follow-up was 4.33 months (range 1 to 6 months). The mean UDVA improved from 0.95 logarithm of the minimum angle of resolution (logMAR) ± 0.33 (SD) to 0.53 ± 0.35 logMAR (P =.001) and the mean CDVA from 0.39 ± 0.22 logMAR to 0.26 ± 0.21 logMAR (P =.09). The mean sphere decreased from −5.08 ± 3.74 diopters (D) to −1.67 ± 2.59 D, the mean cylinder from −5.83 ± 2.02 D to −2.72 ± 1.81 D, and the mean MRSE from −8.03 ± 3.88 D to −3.01 ± 2.82 D (P <.001). The mean K decreased from 51.43 ± 3.59 D to 47.42 ± 3.59 D (P <.001). All patients with a preoperative mean K greater than 55.0 D had worse CDVA. Conclusions Implantation of a 340-degree ICR using femtosecond laser improved the visual, refractive, and topographic parameters in keratoconic patients. The findings indicate that patients with severe keratoconus (mean K >55.0 D) are not good candidates for this type of ICR.