Corneal Safety and Stability in Cases of Small Incision Lenticule Extraction with Collagen Cross-Linking (SMILE Xtra)

Abstract

Purpose. To assess the safety and stability in cases of small incision lenticule extraction with collagen cross-linking (SMILE Xtra). Methods. This study was a retrospective interventional comparative study that included 60 eyes of 30 patients divided equally into two groups: SMILE Xtra and SMILE alone. The inclusion criteria were patients >18 years of age, myopic error >6 D, thinner cornea <520 microns, and abnormal corneal topography. Outcome data were recorded including uncorrected distance visual acuity and corrected distance visual acuity (UDVA and CDVA), manifest refraction spherical equivalent (MRSE), central corneal thickness, average keratometry, endothelial cell density, corneal resistance factor (CRF), and corneal densitometry. The follow-up period was 24 months. Results. There was a significant difference between the 2 groups regarding UDVA, CDVA, and MRSE at 1 month. In the SMILE Xtra group, 90% of eyes had postoperative UDVA of 20/20 and 97% had UDVA of 20/30 at 24 months. At 24 months, 26 eyes (87%) vs. 25 eyes (84%) were within ±0.50 D of attempted correction in SMILE Xtra and SMILE groups, respectively. Regarding stability, both groups showed improvement of MRSE at 1st month postoperatively and remained stable along the 24 months of follow-up. CRF and corneal densitometry were higher in the SMILE Xtra group along the whole follow-up period (p=0.001). Conclusion. Combining corneal cross-linking with SMILE procedure (SMILE Xtra) is a promising tool to prevent ectasia in high-risk patients. It is a safe and simple procedure that can be offered to patients undergoing SMILE with risk for ectasia. Trial registration no: PACTR201810577524718.

Corneal refractive surgery combined with simultaneous corneal cross‐linking: Indications, protocols and clinical outcomes—A review

“…Another study 40 indicated that corneal resistance factor (CRF) was higher in the SMILE Xtra group in the postoperative period, but significantly lower than the preoperative levels. Tomita et al 51 reported the mean preoperative and postoperative change in all dynamic bidirectional applanation device parameters 3, 6 and 12 months postoperatively.…”

“…Overall, there were no statistically significant differences between LASIK-only eyes and LASIK-CXL eyes. Another study 40 indicated that corneal resistance factor (CRF) was higher in the SMILE Xtra group in the postoperative period, but significantly lower than the preoperative levels.…”

“…14,17,43,44 For SMILE Xtra and PRK Xtra, it has been suggested that patients were to be older than 18 years. [37][38][39][40][41] There is no clear-cut evidence for setting a guideline for age. Since younger patients are at risk for post-refractive surgery corneal ectasia, prophylactic CXL is advised at the time of refractive surgery.…”

“…In published surgical techniques, a bandage contact lens was placed on the ocular surface after LASIK Xtra, 28,29,34,40 PRK Xtra 41 and tPRK Xtra. 52 The lens was removed 1 day after LASIK Xtra, 28,29,34,40 and 4 days after tPRK Xtra. 31 In all comparative studies reported so far, patients received the same postoperative treatment in standard corneal refractive surgery group and in corneal refractive surgery-CXL group.…”

“…At 24 months, the percentage of SE within ±0.50 D of attempted correction in SMILE Xtra was 87%, which was better than that in SMILE only group (84%). 40 A PRK Xtra study reported 41 postoperative UCVA and BCVA of 20 of 20 or better in 92.67% and 96.33% eyes, respectively. Refractive predictability within 0.50 D was achieved in 95.4% of the eyes, which was similar to that in PRK-only group (97.4%) at 1-year visit.…”