Another piece of the refractive-surgery puzzle solved?

Thursday, February 16, 2012
Another piece of the refractive-surgery puzzle solved?

One of the difficulties encountered in ophthalmic clinical practice, initially in tonometry, more recently in refractive surgery and corneal cross-linking, has been the inability to ascertain the biomechanical properties of a particular human cornea in vivo.
A recent paper by Scarelli, Pineda, and Yun of the Yun Lab, Wellman Center for Photomedicine, Harvard Medical School, suggests that that situation could be about to change (Brillouin Optical Microscopy for Corneal Biomechanics. IOVS 2012 53(1): 185 - 190).
To date the main contender for an assessment of the cornea has been the Optical Response Analyzer (Reichert) that assesses the cornea’s response to a controlled puff of air.
The new technique uses Brillouin (Léon Brillouin, 1889-1969, French physicist) optical microscopy to determine the cornea’s elastic modulus and the instrument developed consists essentially of a confocal microscope and a high-speed spectrometer.
It is used to determine the intrinsic viscoelastic properties of the cornea optically although in fact it is using hypersonic acoustic waves generated within the cornea to make its determinations.
The induced acoustic waves result in compressed and rarefied corneal tissue locally that in turn produces altered densities and refractive indices. Those acoustic waves are referred to as acoustic phonons and are produced by irradiating the cornea with a Nd-YAG laser operating at 532 nm.
Traditional Brillouin microscopy is a slow (10-60 minutes) process quite unsuited to clinical applications. What Scarelli et al. have done is made a high-speed, variant that takes less than a second per determination.