Corneal hysteresis using the Reichert ocular response analyser: findings pre- and post-LASIK and LASEK.

PURPOSE: To evaluate and compare corneal hysteresis in patients prior to and following laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK) using the Reichert ocular response analyser (ORA).
METHODS: Corneal hysteresis was recorded prior to and 3 months after corneal laser refractive surgery for myopia. Preoperative corneal hysteresis was correlated with age and preoperative central corneal thickness (CCT). Postoperative corneal hysteresis was correlated with postoperative CCT in both the LASIK and LASEK treatment groups. The correlations between postoperative change in hysteresis and stromal ablation depth, percentage of tissue ablated, optical zone and patient age were also examined.
RESULTS: A total of 84 eyes of 84 patients were involved in the study. LASIK was performed in 63 eyes and LASEK in 21. Mean preoperative corneal hysteresis of all eyes was 10.8 +/- 1.5 mmHg. Mean age, preoperative CCT, corneal hysteresis and ablation profile were similar in both groups. A statistically significant decrease in hysteresis occurred following LASIK (p < 0.01) and LASEK (p < 0.01) with similar decrements observed in both treatment groups. A moderate correlation was found between postoperative hysteresis and postoperative CCT in LASIK (r = 0.7) and LASEK (r = 0.7) treated eyes. A weak correlation was found between postoperative decrease in hysteresis and the parameters examined.
CONCLUSION: Corneal hysteresis decreased following LASIK and LASEK. Similar reductions occurred following both procedures, indicating that LASIK involving a thin 120-mum flap did not induce additional biomechanical change. Postoperative reduction in hysteresis did not correlate with the amount or percentage of corneal tissue removed, nor with optical zone or patient age.