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Stephan Reiss, Marina Hovakimyan, Heinrich Stolz, Rudolf F Guthoff, Oliver Stachs; Optimizing Brillouin spectroscopy for in vivo biomechanical assessment of the eye. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3703.
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Brillouin spectroscopy is a novel optical technology that enables non-invasive determination of the biomechanical properties in ocular tissue. However, the parasitic intense elastic scattering prevents Brillouin measurements under clinical conditions. The aim of our research is to improve and simplify the experimental setup to translate the technology into clinical practice.
An in-house developed very narrow band filter, in the form of a gas cell, in combination with a confocal alignment was implemented in the Brillouin setup. Various filter designs were investigated concerning absorption characteristics depending on working wavelength. Furthermore, the spectrometer setup was optimized to minimize scanning time and laser power. Subsequently, this established method was verified by using porcine corneae.
The developed narrow bandpass filter in combination with a single-VIPA spectrometer enables the Brillouin signal separation in a distance of 0.002 nm from the working wavelength (λ= 780.2456 nm) and detection of about 2×10-5 nm wavelength change (bulk modulus change 0.009 GPa) with an axial resolution of 10 µm. Spatially resolved measurements of extracted animal eyes displayed a significant difference within the cornea. Brillouin-shift changes of about 0.4 GHz (bulk-modulus change of 0.2 GPa) between anterior and posterior cornea were observed. Using a laser power of 12 mW and an electron multiplying CCD camera, this improved system requires less than 0.5 s measurement time per location.
The presented Brillouin system improvements enable the development of a sensitive device for measuring ocular biomechanics. The developed techniques are essential to simplify experimental effort and translate the technology into clinical practice.
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