Comparative evaluation of different corneal cross-linking techniques with respect to biomechanical stability of the cornea

Abstract

Aim - to perform a comparative analysis of the following cross-linking techniques: standard cross-linking (SCXL), local transepithelial femto cross-linking (LTF) and transepithelial intrastromal femto cross-linking with MyoRing implantation (TIF+MyoRing) in experimental animals and patients with progressive stage II-III keratoconus (KC), paying particular attention to the changes in biomechanical stability of the cornea. Material and methods. The experimental series was performed on 20 eyes of 10 rabbits. The animals were divided into 4 groups of 5. Group 1 served as the control, group 2 consisted of animals that underwent SCXL, group 3 - of those after LTF, and group 4 - of those after TIF+MyoRing. Femto step was performed using the IntraLase FS 60 kHz femtosecond laser, cross-linking - with the Evolution machine. The follow-up period was 1 month. Clinical study enrolled 48 patients (45 eyes) with stage II-III KC. Depending on the surgical technique all the patients were divided into 3 groups. In group I (14 eyes, 9 patients), TIF+MyoRing was performed, in group II (16 eyes, 20 patients) - SCXL, in group III (15 eyes, 19 patients) - LTF. The follow-up period was 6 months. Results. The experiment showed a significant increase in rupture resistance of the cornea in all three groups. Six months after surgery, patients from group I demonstrated a 1.0±0.22 mmHg higher corneal resistance factor (CRF) and a 1.0±0.12 mmHg higher corneal hysteresis (CH). In group II, the said parameters increased by 0.8±0.10 mmHg and 0.6±0.16 mmHg, respectively; in group III - by 0.8±0.25 mmHg and 0.6±0.26 mmHg, respectively. In neither group the density of endothelial cells has reduced significantly over the follow-up period. Conclusion. All three methods (LTF, TIF and SCXL) equally increase the biomechanical strength of the cornea and are safe. In patients with progressive stage II-III KC, TIF+MyoRing surgery has yielded an even higher improvement of biomechanical parameters in a 6-month follow-up period, which is due to the combination of mechanical and chemical mechanisms of corneal reinforcement.