Influence of different types of corneal laser refractive surgeries on corneal hysteresis and corneal resistance factor in myopic eyes

Background

Refractive surgery has propelled itself forward to become widely performed surgical procedure nowadays.After the surgery, corneal biomechanics decreases lead to keratoconus and corneal ectasia.Doctors pay more attention to biomechanics changes after refractive surgeries.

Objective

This clinical study was to investigate the influence of different laser refractive surgeries on corneal biomechanics.

Methods

A prospective nonrandomized and controlled clinical study was designed.One hundred and sixty-four eyes of 82 patients with moderate myopia were enrolled.The patients were divided into sub-Bowman keratomileusis（SBK) group (60 eyes of 30 patients), laser in situ keratomileusis（LASIK) group (54 eyes of 27 patients) and laser subepithelial keratomileusis (LASEK) group（50 eyes of 25 patients), with the matched demography among the three groups.Corneal hysteresis (CH) and corneal resistance factor (CRF) were detected by ocular response analyzer (ORA) before and 1 week, 5 months after refractive surgery.The correlations between stromal ablation depth and postoperative changing values of CH or CRF were analyzed.

Results

Significant differences were found in CH and CRF at different time points in the three groups (F_time=41.90, P=0.00; F_time=49.65, P=0.00), and the CH and CRF values were significantly lower 1 week and 5 months after surgery than those before surgery (all at P=0.00). However, no significant difference of CH or CRF was seen at all time points among the three groups (F_group=2.17, P=0.08; F_group=2.67, P=0.07). No correlation was found between corneal ablation depth and CH in 1 week and 5 months after surgery (both at R²=0.000), however, weaker correlations were seen between corneal ablation depth and CRF 1 week and 5 months after surgery (Y=3.253+ 0.010X, R²=0.007; Y=1.073+ 0.021 X, R²= 0.004).

Conclusions

SBK, LASIK and LASEK lead to the change of corneal biomechanics by altering CH and CRF, they play the same influence on cornea.CRF appears to be an useful indicator in evaluating corneal biomechanical changes after laser refractive surgery.

Cornea/physiology; Myopia/surgery; Elastic tissue; Biomechanics; Keratomileusis, laser in situ; Keratomileusis, laser subepithelial; Keratomileusis, sub-Bowman