Abstract
Purpose :
Cross-Linking (CXL) has emerged as a powerful alternative to keratoconus treatment, and several modalities are practiced in the clinic. We investigated the effect of different ex vivo CXL treatments beyond the Dresden Protocol (DP) on corneal mechanical properties, measured using ultrasonic wave-based Optical Coherence Elastography (ACUS-OCE).
Methods :
A custom-built 500 kHz ultrasonic air-coupled transducer co-focused with a swept source Optical Coherence Tomography (OCT) system was used to excite the corneal apex and capture 16 OCT corneal cross-sectional meridians in 1s. Lamb wave propagation speed and average corneal thickness were calculated for each meridian to estimate spatial-dependent corneal stiffness. Measurements were conducted on 12 freshly enucleated ex vivo rabbit corneas pre- and post- three CXL treatments (MedioCross Glaukos Corp, USA): Epithelium-on (epi-on), 0.25% riboflavin (RB) in 1.2% methocel (CXL-TE; n=4); Epithelium-off (epi-off), 0.1% RB in 1.1% hydroxypropyl methylcellulose (CXL-M; n=4); Epi-off, 0.1% RB in 20% Dextran (CXL-D, DP solutions; n=4), using DP regimes (30 min of RB soaking; 30 min of UV irradiation (3 mW/cm2)). Measurements were performed pre-treatment, post-RB, and post-CXL. Changes of corneal thickness, shear modulus (G), and the spatial anisotropy of G (SAG) were evaluated.
Results :
Corneal thickness decreased significantly post CXL-D (-186±35 um, p<0.001) but not post- CXL-M or CXL-TE. Post-RB, G increased significantly only in CXL-D (p<0.003). All CXL treatments produced significant increases (p<0.001) in G, by 7.14±2.93 kPa (CXL-D), 5.26±1.52 kPa (CXL-TE), and 2.79±0.74 kPa (CXL-M), respectively. SAG did not change significantly post-RB or post-CXL.
Conclusions :
All CXL modalities produced isotropic increase of corneal stiffness, although effectiveness differed across treatments. CXL-D (standard DP) produced the largest change of G, and some changes even after RB only. CXL-M was the least effective to increase corneal stiffness, maybe due to absence of Dextran. Interestingly, CXL-TE increased G without Dextran and preserving epithelium, suggesting that interactions between solution dynamics and CXL play a role in treatment effectivity. ACUS-OCE has proved a valuable technique for evaluating the effect of CXL on rabbit corneas ex vivo, and shows promising potential for evaluation of CXL in human patients in vivo.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.