Purchase this article with an account.
Arthur J Sit, Shuai-Chun Lin, Arash Kazemi, Jay W McLaren, Xiaoming Zhang; A Novel Non-Invasive Method for In Vivo Measurement of Ocular Biomechanical Properties. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4820.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Biomechanical properties of the eye are important for understanding the risk of glaucoma. In particular, mechanical deformation of the optic disc during intraocular pressure (IOP) changes may be related to Young’s modulus of elasticity. However, there are no clinically available methods for measuring Young’s modulus in patients. In this study we used a novel method to determine Young’s modulus in normal human eyes from the speed of mechanical wave propagation through the cornea.
Eighteen eyes of 9 healthy subjects (age 44-63 years; mean 51 years) were studied. IOP was measured by using Goldmann applanation tonometry. The elasticity of the cornea was then determined by surface wave elastography. Surface waves were generated in the cornea by a spherical-tipped probe (4 mm diameter) that was placed on the closed eyelid. The probe vibrated through a displacement of less than 1 mm at 100 Hz for 0.1 second and surface waves were monitored by ultrasonography as they propagated around the eye. The speed of wave propagation was determined from the change in wave phase with position, and Young’s modulus was calculated from the measured wave speed by assuming that the cornea behaved as a thin plate. Young’s modulus was determined three times in each eye. The association between IOP and mean elasticity was explored by Pearson correlation. Statistical significance was determined by using generalized estimating equation models to account for possible correlation between fellow eyes of the same subject.
Mean IOP was 12.8 ± 2.7 mmHg (± SD). Mean wave speed in the cornea was 1.82 ± 0.77 m/s at 100 Hz. Young’s modulus of elasticity was 454 ± 100 kPa. Young’s modulus was strongly correlated with IOP (r=0.80; p<0.001; Figure).
Surface wave elastography is an effective non-invasive technique for measurement of ocular biomechanical properties. Young’s modulus of elasticity in normal eyes is strongly affected by IOP, consistent with measurements in cadaver eyes. Our measurements agree with published direct measurements of corneal elasticity in cadaver models. Further work is required to determine if elasticity is altered in glaucoma patients, as well as in other ocular diseases such as keratoconus. In addition, further work is required to determine ocular tissue viscosity by using this technique.
This PDF is available to Subscribers Only