Analysis of corneal biomechanical properties 25 years after myopic photorefractive keratectomy.

PURPOSE: To evaluate corneal biomechanical changes using Corvis ST in patients treated with photorefractive keratectomy (PRK) 25 years ago. METHODS: In this study, 32 post-PRK and 38 normal eyes underwent Corvis ST (CST) assessments. The measured CST factors were: time of highest concavity (HC), time of applanation 1 (AT1), time of applanation 2 (AT2), length of applanation 1 (AL1), length of applanation 2 (AL2), velocity of applanation 1 (AV1), velocity of applanation 2 (AV2), deformation amplitude (DA), peak distance (PD), integrated radius (IR), Ambrosio relational thickness horizontal (ARTh), stiffness parameter at first applanation (SP-A1), DA ratio (2 mm), Belin/Ambrosio enhanced ectasia display (BAD) and corneal biomechanical index (CBI). RESULTS: The mean [± standard deviation (SD)] age was 51.4 ± 7.36 years in PRK, 51.4 ± 3.62 in control group. PRK was performed 24.69 ± 1.78 years ago. ARTh, SP-A1, AT1, AL1, and AL2 were lower in PRK. PD, AT2, DA ratio (2 mm), and IR were statistically higher in PRK (P < 0.01). In PRK and control group the mean value of CBI was 0.91 ± 0.11 and 0.50 ± 0.27 (P < 0.001), and mean value of BAD was 3.34 ± 1.53 and 1.1 ± 0.70 (P < 0.001). In PRK 71.9% of eyes were classed "high risk CBI plus diseased BAD" and 25% remained in the "high risk CBI and normal BAD" group. CONCLUSIONS: In this study, most of the post-PRK eyes which were clinically and topographically normal were classified as "high risk CBI plus diseased BAD" and had significantly worse CBI and BAD values than the control group. This leads to the conclusion that CBI and BAD alone are not appropriate to evaluate post-PRK ectasia.