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

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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.