Biomechanical Effects of Custom Corneal Cross-Linking Using Optical Coherence Elastography
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Keratoconus is a progressive disease of the eye which causes the cornea to become weak and thin. If untreated, it may lead to corneal deformation and impaired vision. Corneal collagen cross-linking (CXL) is a recently FDA-approved treatment for keratoconus that stiffens the cornea by the combined use of a photoactivator and exposure to ultraviolet (UV) light. Normal CXL treats a large region of the cornea; in contrast, custom CXL only treats diseased portions of the cornea, minimizing patient exposure to harmful UV light. However, the effects of custom CXL on local corneal stiffness are not well understood. Using a porcine model, we investigated the biomechanical effects of custom CXL. Three dimensional optical coherence tomography (OCT) images of eyes were taken before and after CXL treatment and could distinguish the CXL regions from the untreated areas. To quantify the biomechanical effects of custom CXL, we used optical coherence elastography (OCE), which utilizes OCT imaging to measure air-pulse-induced displacements in the cornea. By varying the induced air pressure, the displacement as a function of applied pressures was quantified, which was a noncontact analog to traditional stiffness measurements by mechanical testing. The OCE measurements were made at points within the CXL and untreated regions. The results showed a statistically significant decrease in the air-pressure-induced displacement response in the CXL region as compared to untreated regions, indicating a significant increase in stiffness. Our work provides both qualitative and quantitative evidence that custom CXL is an effective method of inducing localized stiffening of the cornea.