Noninvasive measurement of scleral stiffness and tangent modulus in porcine eyes.

Abstract

PURPOSE: We investigated an indentation technique to measure the scleral stiffness and tangent modulus of porcine eyes. METHODS: The scleral load-displacement responses were measured with a universal testing machine as a function of IOP in 15 porcine eyes ex vivo using a 5-mm diameter cylindrical flat-punch indenter. The scleral radius of curvature and scleral thickness were measured using a DSLR camera (Alpha 900) and a camera-mounted stereomicroscope (M205C), respectively. The relationships between scleral stiffness, tangent modulus, and IOP were examined. RESULTS: The mean local scleral radius of curvature and scleral thickness were 7.86 &#xb1; 0.49 and 1.03 &#xb1; 0.14 mm, respectively. The average scleral stiffness and scleral tangent modulus of porcine eyes were 0.13 &#xb1; 0.02 N/mm and 0.20 &#xb1; 0.04 MPa at 15 mm Hg, respectively. The scleral stiffness and scleral tangent modulus were correlated positively with IOP (scleral stiffness, 0.989 < r < 0.999, P < 0.001; scleral tangent modulus, 0.989 < r < 0.999, P < 0.001). CONCLUSIONS: The scleral indentation technique can provide a noninvasive approach to measure scleral stiffness and tangent modulus.