Purpose: To assess alterations in parameters measured by the ocular response analyzer (ORA) after photorefractive keratectomy (PRK) with or without 0.02% mitomycin C (MMC) in myopic eyes.Methods: In 33 right eyes of 33 patients, IOP was determined using the Goldmann applanation tonometry (GAT) before and 3 months after PRK. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmanncorrelated IOP (IOPg), and cornea-compensated IOP (IOPcc) were also measured. Pre- and postoperative values were compared and the effect of ablation depth, optical zone, and duration of MMC application on changes in corneal biomechanics was examined.Results: Mean ablation depth was 56.6±20.8 microns. Postoperatively, there was a significant reduction in corneal biomechanical properties and IOP readings by the GAT and ORA. Ablation depth was significantly associated with percentage change in CH (P=0.021), CRF (P=0.001), and IOP GAT (P<0.001). However, the size of optical zone and duration of MMC application was not correlated with these parameters. The percentage of change in IOP GAT and in IOPg but not in IOPcc was significantly associated with percentage of change in CH and in CRF.Conclusion: PRK reduces corneal biomechanical properties which is proportional to the amount of ablation.However, other variables including optical zone and duration of MMC application have no effect. IOPcc appeared to be less dependent on alterations in corneal properties than IOPg and IOP GAT.

Purpose: To evaluate corneal hysteresis and corneal resistance factor in penetrating keratoplasty grafts in a group of keratoconic eyes using the ocular response analyzer (ORA) and to evaluate the relationship between donor size, donor-recipient disparity and central graft thickness (CGT), and ORA parameters.Methods: This cross-sectional study was conducted on 34 eyes of 34 keratoconus patients who had undergone PKP. Corneal hysteresis (CH), corneal resistance factor (CRF), and cornea-compensated intraocular pressure were measured at least 6 months after complete suture removal. Two groups of donorrecipient disparity (0.25 vs. 0.50 mm) were compared using the independent t test. Multivariate regression analysis was used to investigate the correlation of donor trephine size and CGT with ORA parameters. Factors influencing intraocular pressure measured with the Goldmann applanation tonometer (IOP GAT) after PKP were determined using multiple regression analysis.Results: Mean patient age and follow-up period were 29.6±6.2 years and 82.4±59.6 months, respectively. Mean CGT, CH, and CRF were 567.5±38.8 mm, 10.2±2.1 mm Hg, and 10.1±2.2 mm Hg, respectively. CH and CRF had a significant positive correlation with donor trephine size and CGT. Significantly greater values of CH and CRF were observed in the 0.5-mm disparity group compared with the 0.25-mm disparity group. Among the studied parameters, only CH, CRF, and cornea-compensated intraocular pressure had a significant positive correlation with IOP GAT.Conclusion: Graft biomechanics seem to be closer to normal values with larger grafts and greater donorrecipient disparity. These metrics had a significant correlation with IOP GAT after PKP.