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David Touboul, Jean-Luc Gennisson, Thu-Mai Nguyen, Antoine Robinet, Cynthia J. Roberts, Mickael Tanter, Nicolas Grenier; Supersonic Shear Wave Elastography for the In Vivo Evaluation of Transepithelial Corneal Collagen Cross-Linking. Invest. Ophthalmol. Vis. Sci. 2014;55(3):1976-1984. doi: 10.1167/iovs.13-13445.
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© ARVO (1962-2015); The Authors (2016-present)
To assess corneal stiffening with supersonic shear wave imaging (SSI) technology in an experimental model of iontophoresis-assisted transepithelial corneal collagen cross-linking (I-CXL).
Six rabbits underwent full, central I-CXL in one eye. The contralateral eye served as control. In vivo iontophoresis was used for 10 minutes to perform transepithelial delivery of riboflavin prior to UV-A irradiation. Accelerated UV-A protocol was applied for 9 minutes with a 10-mW/cm2 irradiance. Animals were killed and both treated and control corneas were then immediately mounted on a corneal artificial anterior chamber and internal pressure was varied from 15 to 50 mm Hg in 5-mm Hg increments. Swelling was evaluated via central corneal thickness measurements. Ex vivo inflation tests were monitored using SSI technology that provides real-time mapping of the corneal elasticity.
Corneal yellowing of the central 9-mm diameter area was clearly visible in the iontophoresis area of all treated eyes. Elasticity versus internal pressure revealed significant differences of the change in elasticity coefficient with pressure between I-CXL–treated and control corneas with a mean slope that was 27.1 and 16.9 kPa/mm Hg, respectively (P = 0.029). Differences in elasticity at individual pressure levels between groups were statistically significant above 40 mm Hg (P < 0.05).
Intraocular pressure variations were the most important limitations for in vivo stiffness monitoring with SSI because stiffness is a function of internal pressure. Supersonic shear wave imaging succeeded in comparing corneas that underwent I-CXL by performing ex vivo inflation tests where pressure was controlled. Iontophoresis-assisted transepithelial corneal collagen cross-linking corneas exhibited increased resistance to pressure rise, indicating stiffening. In vivo I-CXL and ex vivo SSI is an interesting model to evaluate the sole effect of photopolymerization occurring in the CXL process close to physiological conditions.
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