A new model for evaluating corneal wound strength in the rabbit

Presented in this report is a new model to evaluate corneal wound strength quantitatively by using an Instron 1125 tensiometer with video monitoring. Twenty-six rabbits received full thickness 8 mm central corneal incisions that were marked with sutures at each end and dressed with collagen shields. Animals were killed and corneas were harvested from 3-30 d postoperatively. Tensile test specimens, of rectangular (n = 9) or hourglass (n = 17) planform geometry, were prepared. Uniaxial tension tests were performed on these specimens parallel to the long dimension and perpendicular to the incision. Specimens were processed for light microscopy. Individual specimen load and displacement records were normalized to yield geometry independent stress and strain data sets. Maximum wound strength was determined as peak tissue stress on loading. Maximum tissue stiffness (inverse compliance) was derived from the peak slope of the stress-strain profile. Tissue fracture toughness was calculated as the total area under the stress-strain profile from the onset of loading to total wound failure. Data points at 3, 5, 10, 18, and 30 d show maximum wound strength increasing from 15.2 to 832 kilopascals (KPa), maximum stiffness increasing from 0.20 to 11.4 megapascals, and fracture toughness increasing from 1.82 to 87.7 KPa. Histological observations correlate well with tensiometry deductions. These data suggest enhanced mechanical load bearing with time, indicative of enhanced collagen fiber formation and cross-linking.