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Giuliano Scarcelli, Roberto Pineda, III, Seok H. Yun; Three-dimensional Measurement Of Corneal Biomechanical Properties With Brillouin Optical Microscopy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4383.
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The biomechanical properties of corneal tissue are linked to a number of ocular problems, such as corneal ectasia. We have recently developed Brillouin optical microscopy for non-contact 3D mechanical imaging [Scarcelli and Yun, Nature Photonics, 44, 2008]. Here, we test the feasibility of this technique for quantitative assessment of the cornea ex vivo.
Brillouin light scattering in the tissue gives rise to a small spectral shift that is proportional to the hypersonic elastic modulus. Brillouin optical microscopy measures the Brillouin frequency shift with an ultrahigh-resolution spectrometer in combination with a laser-scanning confocal microscope. A spatial map of the material modulus is obtained in three dimensions with microscopic resolution, as a low-power laser beam is scanned over the cornea. We tested if the technique can detect the corneal tissue stiffening due to collagen crosslinking and distinguish keratoconus vs normal corneas based on their elastic modulus.
We were able to obtain 3D Brillouin elasticity images of cornea, for the first time to our knowledge. The images revealed a depth-dependent variation of the elastic modulus from a stiffer anterior stroma to a more flaccid posterior stroma in bovine corneas ex vivo. Axial scans clearly revealed a stiffening of the anterior stroma induced by Riboflavin corneal collagen photo-crosslinking. In addition, human corneas from keratoconus patients were analyzed and measured to have markedly lower elastic moduli than normal corneas.
Brillouin imaging can quantitatively assess the 3D biomechanical properties of cornea in situ with micron-scale resolution. This novel technique may have the potential for clinical diagnostics and treatment monitoring.
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