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Giuliano Scarcelli, Sebastien Besner, Roberto Pineda, Seok H Yun; High-resolution biomechanical characterization of keratoconus cornea ex vivo with Brillouin microscopy.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3716.
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Abnormal loss of corneal strength is a central feature and an early sign of keratoconus progression. The ability to measure corneal elasticity could dramatically improve the management of keratoconus. However, current clinical instruments only provide morphological information. The objective of this study is to use a recently developed Brillouin microscopy technique for quantifying the corneal mechanical properties of normal vs. keratoconus human corneas.
We have measured eight normal corneas vs. eight advanced keratoconus corneas obtained as discarded tissues after surgery. To have comparable samples, normal corneas were obtained after DSEK surgery (donor cornea, ~70% anterior portion of total corneal depth) whereas advanced keratoconus corneas were obtained after DALK surgery (acceptor cornea, ~85% anterior portion of the cornea). A confocal Brillouin microscope was used to map the Brillouin elastic modulus of the corneas. From the Brillouin maps, the average anterior modulus and the rate of elasticity change with depth were computed.
Brillouin corneal modulus was significantly lower in keratoconus corneas compared to normal (p<0.001) and decreased more rapidly with depth in keratoconus corneas compared to normal (p<0.001). Brillouin microscopy can clearly differentiate between normal and diseased state, and the difference suggests that the stiffness of cornea decreases as keratoconus progresses. The post-mortem corneas showed more pronounced swelling in posterior portions of the cornea, and the swelling was more significant in the keratoconus samples, implying that post-mortem swelling increases in softer portions of corneal tissue.
Brillouin microscopy allowed imaging and quantification of the changes in elastic modulus of the cornea due to keratoconus progression. Our results demonstrate the feasibility of measuring corneal elasticity at high resolution and obtain elasticity-based metrics highly relevant for early diagnostic of keratoconus, monitoring of progression and therapy development.
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