Evaluation of Biomechanical Changes in Myopia Patients with Unsatisfactory Corneas After Femto Second-Laser In Situ Keratomileusis (FS-LASIK) Concurrent with Accelerated Corneal Collagen Cross-Linking Using Corvis-ST: Two-Year Follow-Up Results

Abstract

BACKGROUND Some myopia patients with unsatisfactory corneas consider corneal refractive surgery for different reasons. Accelerated corneal collagen crosslinking (ACXL) is an effective method to enhance the resistance of the cornea. The present investigation was designed to evaluate the changes of biomechanical properties in patients with myopia and thin corneas after femtosecond-laser in situ keratomileusis (FS-LASIK) concurrent with ACXL. MATERIAL AND METHODS A prospective study was designed. A total of 22 eyes of 11 myopia astigmatism patients with unsatisfactory corneas were enrolled. The patients were assigned to femtosecond-laser in situ keratomileusis concurrent with accelerated corneal collagen crosslinking (FS-LASIK-ACXL). The follow-up duration was 24 months. Manifest refraction, uncorrected (UDVA), and corrected distance visual acuity (CDVA), ultra-high-speed camera (Corvis-ST), corneal topography, anterior segment OCT (AS-OCT), Pentacam, and endothelial cell density (ECD) were examined before and after the operation. The corneal biomechanical and refractive data was analyzed using SAS9.3. Data were analyzed through normal distribution test and variance of analysis. The difference was considered as statistically significant when p<0.05. RESULTS The steep K (Ks) values, flat K (Kf) values, average keratometry values (Avek) values, and central corneal thickness (CCT) declined significantly after FS-LASIK-ACXL operation. The values of first applanation length (A1L), the second applanation length (A2L), the first applanation velocity (A1V), the second applanation velocity (A2V), deformation amplitude (DA), highest concavity peak distance (PD), and radius of curvature at the time of highest concavity (HCR) did not show significant difference after the operation. CONCLUSIONS FS-LASIK-ACXL is an effective and safe surgery for improving visual acuity for myopic patients with thin corneas, and it does not increase the risk of iatrogenic keratectasia.

Figure 1

A1L and A2L changes before the operation and at 1, 3, 6, 12, and 24 months after the operation. 0: before surgery; 1: 1 month after surgery; 3: 3 months after surgery; 6: 6 months after surgery; 12: 12 months after surgery; 24: 24 months after surgery. (A) After FS-LASIK-ACXL, the mean A1L declined; however, the difference did not show statistical significance between pre- and post-operation. (B) After the operation, mean A2L increased, which did not show statistical significance between pre- and post-operation.

Figure 2

A1V and A2V changes before the operation and at 1, 3, 6, 12, and 24 months after the operation. 0: before surgery; 1: 1 month after surgery; 3: 3 months after surgery; 6: 6 months after surgery; 12: 12 months after surgery; 24: 24 months after surgery. (A) After FS-LASIK-ACXL, the mean A1L declined; however, the difference did not show statistical significances between pre- and post-operation. At different follow-up time points, the trend showed a little fluctuation, but no statistical significance. (B) After the operation, the mean A2L declined, which did not show statistical significance between pre- and post-operation.

Figure 3

DA, PD, and HCR changes before the operation and at 1, 3, 6, 12, and 24 months after the operation. 0: before surgery; 1: 1 month after surgery; 3: 3 months after surgery; 6: 6 months after surgery; 12: 12 months after surgery; 24: 24 months after surgery. (A) After the operation, the mean DA declined; however, the difference did now show statistical significance between pre- and post-operation. (B) After the operation, the mean PD increased; however, the difference did not show statistical significances between pre- and post-operation. (C) After the operation, the mean HCR declined; however, the difference did not show statistical significance between pre- and post-operation.