Intrastromal Injection of Hyaluronidase Alters the Structural and Biomechanical Properties of the Corneal Stroma

Abstract

PurposeGlycosaminoglycans (GAGs) are important components of the corneal stroma, and their spatiotemporal arrangement regulates the organization of collagen fibrils and maintains corneal transparency. This study was undertaken to determine the consequences of hyaluronidase (HAse) injected into the corneal stroma on stromal stiffness and ultrastructure.MethodsEqual volumes of HAse or balanced salt solution (vehicle) were injected intrastromally into the corneas of New Zealand white rabbits. Ophthalmic examination and multimodal imaging techniques, including Fourier-domain optical coherence tomography and in vivo confocal microscopy (IVCM), were performed at multiple time points to evaluate the impact of HAse treatment in vivo. Atomic force microscopy and transmission electron microscopy (TEM) were used to measure corneal stiffness and collagen's interfibrillar spacing, respectively.ResultsCentral corneal thickness progressively decreased after HAse injection, reaching its lowest value at day 7, and then returned to normal by day 42. The HAse did not impact the corneal endothelium but transiently altered keratocyte morphology at days 1 and 7, as measured by IVCM. HAse-injected corneas became stiffer by day 1 postinjection, were stiffest at day 7, and returned to preinjection values by day 90. Changes in stromal stiffness correlated with decreased interfibrillar spacing as measured by TEM.ConclusionsDegradation of GAGs by HAse decreases the corneal thickness and increases stromal stiffness through increased packing of the collagen fibrils in a time-dependent manner.Translational RelevanceIntrastromal HAse injection appears relatively safe in the normal cornea, but its impact on corneal biomechanics and structure under pathologic conditions requires further study.