Analysis of the sclera elasticity properties and comparison with corneal biomechanics properties in vivo and in vitro.

Objective: To explore scleral elastic modulus and its correlation with corneal biomechanics in vivo and in vitro, and to introduce a predictive model for non-destructive characterization of scleral and corneal elastic modulus.

Methods: In vivo biomechanical parameters of 21 rabbit eyes were measured using the Corvis ST. Uniaxial tensile tests on corneal and scleral (anterior, equatorial, and posterior sections) strips provided low-strain and high-strain tangent elastic modulus (LSTM and HSTM). Pearson's and Spearman's correlation analyses were used to examine the relationship. A multivariate linear regression model was used to characterize the elastic modulus in vivo. Transmission electron microscopy was used to elucidate the arrangement of collagen fibers in the anterior, equatorial, and posterior sclera.

Results: Twelve in vivo parameters significantly correlate with the corneal LSTM (P < 0.05), whereas no parameters are correlated with the corneal HSTM. SP-HC (Rho=0.442) and HC Deflection Amp (HC DA, r=-0.605) correlated with anterior sclera LSTM. DA ratio 1 mm (r=0.446) was correlated with the equatorial sclera LSTM. Integrated Radius (Rho=0.483) and Radius (r=-0.473) were correlated with the equatorial sclera HSTM. The representative multivariate linear regression model indicated the follows: Corneal LSTM = 0.046 + 0.01 * SP-A1 + 0.066 * SSI Anterior sclera LSTM = 0.294 - 0.120 * HC DA Equatorial sclera LSTM = 0.22 + 0.114 * DA Ratio 1 mm - 0.049 * HC DA

Conclusions: Biomechanical parameters, such as SP-A1 and SSI, correlate with the low-strain elasticity of the cornea, which primarily reflects the properties of the corneal ground matrix. Corvis ST may not be able to detect biomechanics changes in the cornea collagen structure. The scleral elastic modulus prediction model offers new insights into the non-destructive characterization of scleral biomechanics.