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Michael Bukshtab, Amit Paranjape, Marc D Friedman, David Muller; Confocal Brillouin spectrometer for measuring corneal biomechanics. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1102.
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Current methods for in-vivo measurement of corneal biomechanics are inadequate. This presents an impediment to diagnosis and treatment of corneal conditions such as keratoconus. Brillouin spectroscopy provides a non-contact, objective method to measure mechanical properties. This study developed a non-contact, confocal Brillouin spectrometer, capable of millisecond signal acquisition times, for measurement of corneal biomechanics.
A highly-sensitive confocal microscope-spectrometer was built to detect Brillouin signal shifts. The system utilizes an eye-safe, highly coherent, single-frequency, fiber-coupled laser at 780 nm wavelength, stabilized at the Rubidium D2 absorption line. A polarization-extinction scheme and confocal fiber optic system were used to collect Brillouin shifted light scatter. This system in conjunction with a rubidium filtering cell (to reduce Rayleigh scattering and stray-light of the excitation wavelength) analyzes the Brillouin signal with an enhanced VIPA spectrometer and low-noise EMCCD camera.<br /> The system was tested by measuring fresh porcine corneas with and without cross-linking. Crosslinking was performed at UVA doses of 0 to 20 J/cm2 with irradiances of 3 to 30 mW/cm2 using 0.12% riboflavin solution.
Microsecond acquisition-time sensitivity for corneal biomechanics was demonstrated via Brillouin spectroscopy measurements. Brillouin spectral shifts ranging from 7.8 to 8.7 GHz were observed for porcine specimens, with cross-linked eyes showing linear increase as a function of CXL dose as compared to non-cross-linked eyes.
A non-contact, confocal Brillouin scanning microscope-spectrometer is demonstrated. This device allows measurement of the biomechanical, spatial distribution of corneal tissue and is able to differentiate CXL treated tissue. This system holds future promise as a tool to enhance corneal diagnostics and corneal cross-linking treatments.
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