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Carlos Dorronsoro, Daniel Pascual, Pablo Pérez-Merino, Sabine Kling, Susana Marcos; Changes In Corneal Air Puff Deformation Parameters After Cross-Linking From Dynamic OCT. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1519.
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© ARVO (1962-2015); The Authors (2016-present)
To retrieve quantitative corneal biomechanical properties in-vivo and non-invasively, from high-speed OCT images of the dynamic response of the cornea to an air puff inducing a deformation.
A spectral OCT instrument combined with an air tonometer in a non-collinear configuration was used to image the corneal deformation over full corneal cross-sections, as well as to obtain high speed measurements of the temporal evolution of the corneal apex. With this new technique the entire deformation process can be dynamically visualized. A quantitative analysis allows direct extraction of several deformation parameters. The potential of the technique is demonstrated in vitro on porcine corneas under controlled IOP for different conditions (untreated, de-epithelialized, after Riboflavin instillation, and after UV-cross-linking, CXL), as well as in vivo in humans.
Corneal deformation dynamics varied significantly across species and treatments. Despite its lower thickness, the living human cornea showed lower deformation amplitude (0.56 mm) than porcine untreated corneas (0.85 mm), shorter deformation durations (14.3 vs 17.3 ms) and reduced recovery speeds (0.11 vs 0.21 mm/ms). CXL (and, to a minor extent, Riboflavin) decreased corneal thickness by 50% and reduced several deformation parameters in comparison to those of virgin corneas: deformation amplitude from 0.85 to 0.61 mm, deformation diameters from 5.7 to 4.4 mm, displaced volumes from 10.1 to 4.0 mm3, and recovery speed from 0.21 to 0.12 mm/ms. CXL also produced changes in the temporal symmetry of the deformation, advancing the peak deformation time. These differences are consistent with increased corneal stiffness following CXL.
High-speed OCT in combination with air-puff allowed one- and two-dimensional tracking and quantification of corneal deformation events in vivo and in vitro. The differences in the corneal response across treatments (i.e. Riboflavin vs CXL) to the same deformation stimulus are likely the result of changes in the microscopic structure of the cornea, and not a consequence of changes in corneal thickness, geometry or IOP across conditions. Combinations of these measurements with finite element modelling will allow quantification of the biomechanical properties of corneal tissue, at an individual level and in vivo, to improve diagnosis and prognosis of diseases and treatments.
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