Biomechanical mapping of the optic nerve head and peripapillary sclera using high frequency ultrasonic elastography

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Project Summary Glaucoma is a leading cause of irreversible blindness worldwide, affecting over 2.2 million Americans. With an aging population, it is estimated that by 2020 the number of people suffering from glaucoma will reach 80 million worldwide, with 11 million being bilaterally blind. Although elevated intraocular pressure (IOP) is the primary risk factor for the development of glaucomatous optic nerve damage , the mechanisms by which elevated IOP eventually leads to damage are still unclear. Thus, there is a need to develop novel non-invasive imaging modalities that can measure the fundamental mechanical properties of the posterior sclera, and characterize how they contribute to damage in patients particularly as it relates to age, race, and severity of glaucomatous damage. Such a tool would be an important step forward in ocular research and clinical practice, providing the much-needed ability to evaluate the risk of disease based on person- and eye-specific characteristics. The goal of this study is to develop a novel high-resolution ultrasound-based imaging platform non-invasively measure biomechanical properties of the posterior sclera. To address this goal, we propose two imaging systems utilizing dual frequency configuration. One system consists of a low-frequency (4.5 MHz) ring shape transducer to “push” the tissue, and a needle single element transducer inside to “track” micron-level displacement; Another system is to replace the needle transducer with a high-frequency single crystal linear phased array as receiver for elastography imaging to first acquire real time and high speed elastography imaging of the posterior sclera. 2D/3D acoustic radiation force impulse (ARFI) imaging and shear wave elasticity imaging (SWEI) will be performed on ex-vivo unscaled rabbit sclera that will be preloaded with various IOP levels for evaluation. Our preliminary results have demonstrated the principle of using the dual frequency ultrasonic elastography technique on obtaining the biomechanical properties of the sclera and cornea. Integrating high-resolution ARFI imaging with quantified tissue stiffness measurements via the propagation speed of the associated shear wave can potentially allow us to characterize in detail the association between age and gender on the mechanical properties of the sclera and allow us to explore the relationship with glaucoma