• refractive stability, UCVA, BSCVA, complications
  

Subjects and Methods

Ethical committee approval was obtained for the original trial, and patients were asked to sign an informed consent form (in accordance with Institutional guidelines and to the Declaration of Helsinki) before treatment and for further follow-up examinations. The registration information for this clinical trial is available to the public through the National Institute of Health database.

The surgical procedure was done under topical anesthesia. Two Intacs segments of 0.45-mm thickness were inserted so as to embrace the steepest keratoconus meridian, according to the topographic image, aiming at maximal flattening.

The corneal thickness was measured intraoperatively at the incision site and peripherally in the cornea along the ring placement markings with ultrasonic pachymetry (Sonogage, Cleveland, Ohio, USA). Using a diamond knife, set at 70% of the thinnest corneal measurement, a 0.9-mm radial incision was formed, and corneal pockets were created using two Sinskey hooks and a Suarez spreader. Two corneal tunnels were then formed using clockwise and counterclockwise dissectors under suction created by a vacuum-centering guide. The two polymethyl methacrylate (PMMA) segments (0.45-mm thickness) were implanted in the respective corneal tunnels, maintaining a space of approximately 2.0-mm between their ends and 1.5 mm between the opposite edge of each segment and the edge of the incision. The incision site was sutured using a single 10/0 nylon stitch.

Postoperative evaluation Postoperatively, all eyes received antibiotic/steroid combination eye drops 4 times per day for 2 weeks. In addition, all patients were instructed to use preservative-free artificial tears frequently. The sutures were removed 2 weeks after surgery.

Group differences for continuous variables were tested using the paired Student t tests. The change in manifest refraction (spherical equivalent) (MRSE) and topographic k values and topographic astigmatism were plotted over time to determine long-term stability, and the difference as a function of time was analyzed using paired 2-tailed t tests (at time intervals of preoperative to 1 month, 1 to 3 months, 3 to 6 months, 6 to 12 months, and every year of follow up period). Results are presented as means + standard deviation [SD]. A P value less than .05 was regarded as statistically significant.