Purpose:

To investigate the changes in corneal biomechanical properties measured by Reichert’s ocular response analyzer (ORA) after femtosecond laser assisted laser in situ keratomileusis (LASIK).

Methods:

This study was planned prospectively in refractive surgery patients with myopia and myopic astigmatism. Forty six eyes of 23 patients were included in the study. Femtosecond laser assisted LASIK was performed in all eyes as surgical technique. ORA measurements were taken preoperatively and at 1.day, 1.week and 1.month postoperatively. Measured parameters were corneal-compensated intraocular pressure(IOPcc), Goldmann-correlated intraocular pressure (IOPg), corneal resistance factor(CRF) and corneal hysteresis(CH). Central corneal thickness(CCT) was measured by ultrasonic pachymeter pre- and postoperatively. Statistical evaluation was performed using Student’s t test, paired t test and Pearson correlation test; a p value of less than 0.05 was considered to be statistically significant.

Results:

Mean spherical equivalence of preoperative refraction was -3.24±2.79 diopters(D). Mean preoperative CCT was 541.5±18.36 µm whereas mean postoperative CCT at 1.month was measured 441.75±21.28 µm. Mean preoperative ORA parameters were as follows: IOPcc 16.07±2.67 mmHg, IOPg 16.42±3.13 mmHg, CRF 11.24±1.58 mmHg, CH 11.05±1.24mmHg. Mean postoperative ORA parameters at 1.day were IOPcc 16.32±2.58 mmHg, IOPg 16.13±2.86 mmHg, CRF 10.76 ± 1.43, CH 10.58±1.20 mmHg. Mean postoperative ORA parameters at 1.week were IOPcc 16.03±3.41 mmHg, IOPg 13.47±3.91 mmHg, CRF 8.39±2.08, CH 8.78±1.70 mmHg. Mean postoperative ORA parameters at 1. month were IOPcc 15.09±2.28 mmHg, IOPg 13.23±3.85, CRF 8.45±2.41 mmHg, CH 9.14±1.65 mmHg. Difference between mean preoperative CH and mean postoperative CH at 1.month was found to be highly statistically significant (p<.0001).

Conclusion:

Some parameters of ORA change after femtosecond laser assisted LASIK. IOPg, CRF and CH were significantly reduced in early postoperative period whereas IOPcc seemed not to be effected.

Keywords: Corneal biomechanics, corneal hysteresis, ocular response analyzer, ORA, femtosecond laser, LASIK.