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PURPOSE: To determine the relative impact of contact lens– assisted corneal cross-linking (CACXL) and standard protocol CXL (CXL) on regional corneal stiffness using Brillouin microscopy. METHODS: CXL and CACXL were performed on 30 intact fresh porcine eyes (15 per group). Depth profile of stiffness variation and averaged elastic modulus of anterior, middle, and posterior stroma were determined by Brillouin maps. Corneas were cut into strips to conduct mechanical stress-strain tests after Brillouin microscopy to evaluate stiffness difference between CXL and CACXL. Each eye served as its own control. RESULTS: CXL had a greater impact on corneal stiffness, with a maximum increase of 5.74% compared to 3.99% for CACXL ( P < .001). CXL increased longitudinal modulus by 7.8% in the anterior, 1.7% in the middle, and −0.7% in the posterior regions compared to CACXL, which increased longitudinal modulus by 5.5% in the anterior ( P < .001), 1.2% in the middle ( P = .15), and −0.4% in the posterior regions ( P = .60). Mechanical stress-strain tests showed that at 10% strain averaged Young's modulus was 5 MPa for CXL and 2.97 MPa for CACXL ( P < .001). CONCLUSIONS: Both CACXL and standard protocol CXL induced significant corneal stiffening primarily concentrated in the anterior cornea. CACXL leads to less stiffening compared with CXL. An attenuated but continuous stiffening effect can be observed through the whole cornea for both CACXL and CXL, although CACXL has a smaller stiffness gradient. [ J Refract Surg . 2019;35(11):721–728.]

Purpose: To identify the best metrics or combination of metrics that provide the highest predictive power between normal eyes and the clinically unaffected eye of patients with highly asymmetric keratoconus using data from a Dual Scheimpflug/Placido device Design: Retrospective case-control study. Methods: Combined Dual Scheimpflug/Placido imaging was obtained from the Galilei G 4 device (Ziemer Ophthalmic Systems AG; Port, Switzerland) in 31 clinically unaffected eyes with highly asymmetric keratoconus and 178 eyes from 178 patients with bilaterally normal corneal examinations that underwent uneventful LASIK with at least one year follow-up. Receiver operating characteristic (ROC) curves were generated to determine area under the curve (AUC), sensitivity, and specificity for 87 metrics, and logistic regression modeling was utilized to determine optimal variable combinations. Results: No individual metric achieved an AUC greater than 0.79. A combined model consisting of 9 metrics yielded an AUC of 0.96, with 90.3% sensitivity and 92.6% specificity. Among those 9 metrics included, 5 related to corneal pachymetry, Opposite Sector Index (OSI) and Anterior Height BFS Z from the anterior surface, Asphericity and Asymmetry Index (AAI), Posterior Height BFS Z, and Posterior Height BFS X from the posterior surface. The strongest variable in the model was the thinnest point location on the horizontal (x) axis.