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Christopher Leung, Cong Ye, Match Ko, Leo Leung, David Lam; A Novel Device for Clinical Measurement of Corneal Elasticity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4012.
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© ARVO (1962-2015); The Authors (2016-present)
The investigation of corneal biomechanics has been obfuscated by the lack of an instrument that can measure corneal elasticity. We have validated the principle of corneal indentation for measurement of corneal elastic modulus (E) in a silicone model of cornea, in porcine eyes (ex vivo testing) and rabbit eyes (in vivo testing). In this study, we designed and built a prototype for measurement of corneal E in glaucoma patients.
The prototype device is portable and designed to fit into a slit-lamp (Fig.1). It has 2 key components: (1) a corneal indenter with a subminiature load cell for measurement of the load, and (2) a miniature linear motorized actuator that propels the indenter and measures the displacement of corneal indentation. The load displacement data are transmitted to a notebook computer via Bluetooth to allow visual display of the load displacement curve. 30 eyes of 15 glaucoma/suspect patients were recruited for measurement of IOP (dynamic contour tonometry), CCT, corneal curvature (K) and corneal E (3 consecutive measurements) in the same visit. The test-retest variability of corneal E was evaluated and the association between IOP and corneal E was examined with linear mixed model.
The mean IOP, CCT and K were 18.5±4.2mmHg, 560.5±35.2µm, and 43.8±1.6D, respectively. Corneal E was derived from the load displacement curve (Fig.2), taking individual K and CCT in the calculation. The corneal E ranged between 0.41 and 0.89 MPa (mean: 0.63±0.11 MPa). The ICC was 0.837 (95% CI: 0.727 - 0.913). There was a significant correlation in corneal E between fellow eyes (r=0.619, p=0.015) and the corneal E was positively associated with IOP (p=0.017) (with adjustment of correlation between fellow eyes).
This study provides an unprecedented documentation of corneal E in human eyes in vivo. Corneal E is often reported with little attention to the preload (the IOP). Our finding indicates that corneal elastic modulus should always be interpreted with IOP.
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