Comparison of corneal biomechanics in pre and post-refractive surgery and keratoconic eyes by Ocular Response Analyser

Purpose: To compare biomechanical parameters measured by the Ocular Response Analyser (ORA) in the form of corneal hysteresis (CH), corneal resistance factor (CRF) and central corneal thickness (CCT) in eyes before and after excimer laser refractive surgery and keratoconic eyes. Setting: Teaching Hospital and private eye clinic in Solihull, UK. Methods: Prospective case comparison of 110 eyes selected for refractive surgery and 132 keratoconic eyes. The CH and CRF of each eye was measured by the ORA. The CCT was measured using ultrasonic pachymetry. Results: The mean preoperative (pre-op) CH for the normal refractive surgery eyes was 11.4 ± 1.9 mmHg, CRF 10.0 ± 1.6 mmHg and CCT 546.5 ± 33.0 μm. Post-operatively CH was 9.2 ± 2.1 mmHg, CRF 7.6 ± 1.8 mmHg and CCT 483.1 ± 40.8 μm. The values for keratoconic eyes were 9.4 ± 2.2 mmHg, 7.7 ± 2.6 mmHg and 488.1 ± 52.6 μm, respectively. The CH, CRF and CCT decreased as the severity of keratoconic eyes increased. All these parameters showed statistically significant difference between normal eyes and keratoconic eyes. This was also the case between post-operative eyes. Conclusion: The biomechanical parameters measured were very similar when comparing keratoconic and post-refractive surgery eyes.