Evaluation of corneal biomechanical behavior in vivo for healthy and keratoconic eyes using the stress-strain index.

PurposeTo evaluate the characteristics of corneal material properties in healthy individuals and keratoconic patients using the stress-strain index (SSI).SettingVincieye Clinic in Milan, Italy, and Instituto de Olhos Renato Ambrósio in Rio de Janeiro, Brazil.DesignRetrospective observational cross-sectional study.MethodsRecords of 1221 patients were divided into 3 groups: healthy corneas (n = 728), bilateral keratoconus (KC, n = 388), and very asymmetric ectasia (VAE, n = 105) when patients presented with clinical ectasia in 1 eye and normal topography (VAE-NT) in the fellow eye. All patients were examined with Pentacam HR and Corvis ST. Severity of KC cases was stratified according to the Pentacam topographic KC classification. The SSI distribution across the different groups and its correlation with age, biomechanically corrected intraocular pressure (bIOP), and central corneal thickness (CCT) were assessed.ResultsA statistically significant difference between healthy individuals and each of the keratoconic groups ( P .050). Among healthy eyes, there was only a mild correlation between the SSI and bIOP ( R = 0.12, P = .002) and CCT ( R = 0.13, P = .001).ConclusionsThis study estimates the in vivo corneal material properties in healthy individuals and patients with KC using a new method. The SSI showed a progressive deterioration within the advance in disease stages while being relatively independent of bIOP and CCT but positively correlated with age