Relationship between initial corneal hydration and stiffening effects of corneal crosslinking treatment

To characterize the mechanical property improvement of riboflavin and ultraviolet light corneal crosslinking (CXL) procedure in artificially swollen human and porcine corneas.

Computational Biomechanics Research Laboratory, Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Illinois, USA.

Experimental study.

Porcine and human donor corneas were crosslinked at different hydration levels using riboflavin-dextran solutions of different osmolality. Four porcine groups (H_w [hydration in mg H₂O/mg dry tissue] = 3.3 ± 0.2 [SD]; 4.0 ± 0.1; 5.1 ± 0.1; 5.6 ± 0.1) and 3 human groups (H_w = 3.2 ± 0.1; 3.9 ± 0.2; 5.3 ± 0.3) were considered. The mechanical properties were measured by uniaxial tensile experiments during which the hydration of samples was the same as the hydration at which they were crosslinked. Tensile properties of 2 porcine groups (H_w = 5.1 ± 0.1; 5.6 ± 0.1) were also measured when their average hydration was lowered to 4.0 mg H₂O/mg dry tissue.

The CXL procedure significantly increased tensile properties of both human and porcine samples in each hydration group (P < .05). The improvement in tensile properties was hydration-dependent, that is, samples crosslinked at higher hydration levels showed lower maximum tensile stress. The behavior of samples crosslinked at different initial hydration but tested mechanically at similar hydration showed insignificant difference (P = .7).

Increasing the hydration of porcine and human corneal samples before the CXL treatment had insignificant influence on tensile property improvement, as measured by testing specimens at similar hydration.