Corneal tensile strength in fully healed radial keratotomy wounds

To investigate the susceptibility to rupture of a human donor cornea with fully healed radial keratotomy (RK) incisions using biomechanical measurement methods and finite element analysis.

A human cornea 8 years after RK was cut into four strips and subjected to tensile testing until rupture occurred. The fellow cornea was pressurized on an artificial anterior chamber beyond the initiation of wound gape. The tensile strengths of nine strips from unincised corneas were measured as controls. To investigate the effect of epithelial plugs on the RK strip test results, a finite element model of a strip containing an epithelial plug was analyzed.

Rupture occurred along the wound site with wide variability in the measured tensile strengths. There was no significant difference in tensile strength between the RK corneal strips (16.6 +/- 4.43 N/mm2) and the control strips (19.1 +/- 3.50 N/mm2). Four of the eight incisions of the fellow RK cornea gaped, but the cornea did not rupture up to a pressure of 2740 mm Hg. An epithelial plug of 10% of the corneal thickness was found in one of the incisions. The finite element results demonstrated higher stresses at the wound site that increased with the size of the epithelial plug.

The presence of an epithelial plug in a fully healed radial keratotomy incision will create a stress concentration at the incision site that may predispose the cornea to rupture. The variability in the strength measurements indicates that the increase in rupture susceptibility due to RK may be hard to predict and may depend on factors such as the size of the plug and the strength of the wound collagen.