Corneal biomechanical properties in keratoconic and normal eyes

Abstract

To compare the corneal biomechanical properties of keratoconic and normal eyes, and to explore the changing characteristics in keratoconic eyes. Case-control study. Thirty-two keratoconic subjects(41 eyes)and 41 subjects(41 eyes)with normal corneas were enrolled in this study. Scheimpflug noncontact tonometry(Corvis ST)was performed to measure the length of Appl 1(1st A length), velocity of Appl 1(Vin), length of Appl 2(2nd A length), velocity of Appl 2(Vout), deformation amplitude(DA), peak distance, and radius. Comparison of the biomechanical property values between the keratoconic and normal eyes was performed using One-Way ANOVA. Pearson or Spearman correlations were used to evaluate the relationship between corneal biomechanical properties and corneal morphology parameters. The areas under ROC curves of the biomechanical properties of Corvis ST were calculated. In the keratoconic group, the values of Vin, Vout, and DA were(0.201±0.268),(0.463±0.121), and(1.146±0.113)mm, respectively, which were obviously greater than the normal group[(0.151±0.017),(0.418±0.060), and(1.146 ± 0.113)mm, respectively; F=6.028, 20.724, 10.606, P=0.016, 0.000, 0.001]. The radius in the keratoconic eyes was(5.898 ± 0.976)mm, apparently shorter than the normal eyes[(7.012 ± 0.728)mm; F=5.277, P=0.023]. In the keratoconic eyes, there were significant correlations between the 1st A length, Vout, DA, radius and the thickness of the thinnest cornea(r=0.330,-0.490,-0.482, 0.676, P=0.035, 0.001, 0.001, 0.000). There were significant correlations between the DA, radius and the anterior surface refractive power Km(r=0.751,-0.528, P=0.044, 0.019). The Vin, Vout, DA, and radius had statistically significant correlations with the maximum posterior surface elevation(r=0.475,-0.552,-0.399, 0.273, P=0.021, 0.015, 0.001, 0.000). The areas under ROC curves of the radius, DA, Vout, and Vin were all greater than 0.9. There were obvious changes of corneal biomechanical properties in keratoconic eyes compared with normal eyes. The radius showed a better sensitivity for the change of corneal biomechanical properties and a major reference value for the diagnosis of keratoconus. (Chin J Ophthalmol, 2016, 52:669-673).