Compression-based optical coherence elastography of the cornea
It is postulated that local changes in corneal biomechanical properties precede structural deformities, and therefore, there is a need for techniques capable of mapping corneal biomechanical properties. In this work, we present a phase-sensitive method of compressional optical coherence elastography (OCE) for mapping corneal stiffness. Preliminary measurements were performed in rabbit corneas in situ (N=3) under various conditions. The compressive strain was not significant as a function of baseline intraocular pressure (IOP) (P=0.989) but did significantly change after UV-A/riboflavin corneal collagen crosslinking (CXL) (P<0.001). Because the in situ eye-globes were cannulated for artificial IOP control, the IOP fluctuations caused by the compressive load could also be quantified. By dividing the change in IOP (ΔIOP) by the measured strain, the stiffness was also quantified and was significantly affected by the baseline IOP (P=0.037) and the CXL treatment (P<0.001). An additional cornea was partially CXL, where only half of the cornea was treated. The average strain in the untreated region was significantly greater (P=0.030) than the strain in the CXL region, and the stiffness as quantified by the ΔIOP/strain was significantly higher in the CXL region as compared to the untreated region (P=0.030). After validation in the in situ rabbit corneas, in vivo measurements were performed in an anesthetized rabbit where the strain significantly decreased after traditional CXL (P<0.001). Partial CXL was also performed on an additional animal, where only half the cornea was treated. The strain in the untreated region was significantly less (P<0.001) than the strain in the CXL region. Our results show the ability of compression-based OCE to measure changes in corneal biomechanical properties in 4 different scenarios (in situ traditional CXL, in situ partial CXL, in vivo traditional CXL, in vivo partial CXL).
University of Houston
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