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Kirill Larin, Manmohan Singh, Chen Wu, Zhaolong Han, Salavat Aglyamov, Michael D Twa; Quantifying the Biomechanical Properties of the Cornea and Lens as a function of IOP with Optical Coherence Elastography. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4692.
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© ARVO (1962-2015); The Authors (2016-present)
To measure biomechanical properties of the cornea and the lens as a function of intraocular pressure (IOP). We have developed a noncontact tonometry technique with optical coherence elastography (OCE) system that can measure corneal geometry, eye-globe IOP, and corneal biomechanical properties. We also present results quantifying the relationship between lens biomechanical properties and IOP.
Fresh whole porcine eyes were utilized in the cornea (n=3) and lens (n=8) experiments in situ. The IOP was fixed at various physiological and pathophysiological levels. To measure IOP, a large air puff induced an inwards and outwards deformation in the corneas, which was imaged by the OCE system at a frame rate of 7.3 kHz. The time at which the cornea was flat during the inward and outward deformation was correlated to the measured air puff pressure to quantify the IOP. Corneal stiffness was estimated by imaging air-pulse induced low amplitude (<10 μm) elastic waves with the same system. The lens biomechanical properties at various IOPs were measured by imaging an acoustic radiation force (ARF) induced displacement at the apex of the lens with a phase-sensitive spectral-domain OCE system.
A student’s t-test showed that the IOP measured by the OCE system was not significantly different from the IOP set by the artificial IOP system (P=0.07). However, IOP measurements by a rebound tonometer did show a very significant difference from the artificially controlled IOP (P<0.001). The stiffness of the cornea was measured as 14.5±2.3, 50.0±2.0, and 158.0±31.8 kPa at IOPs of 10, 15, and 25 mmHg. The lenticular experiments showed that the maximal displacement induced by ARF increased ~23% as the IOP increased from 5 to 20 mmHg. However, as the IOP was further increased to 30 mmHg, there was no noticeable change the maximal displacement. The relaxation rate of ARF-induced mechanical deformations followed a similar trend.
OCE system measured the corneal geometry, eye-globe IOP, and corneal stiffness with a single instrument, providing a more comprehensive measure of ocular health. The stiffness of the lens increased along with IOP up to 20 mmHg, but stabilized as IOP was further increased. These demonstrate that OCE is a powerful tool for noninvasively measuring the biomechanical properties of cornea and lens.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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