Abstract
Assessment of corneal biomechanics for pre- and post-refractive surgery is of great clinical importance. Corneal biomechanics affect vision quality of human eye. Many factors affect corneal biomechanics such as, age, corneal diseases and corneal refractive surgery. There is a need for non-invasive in-vivo measurement of corneal biomechanics due to corneal shape preserving as opposed to ex-vivo measurements that destructs corneal tissue. In this study, a new approach for assessing corneal biomechanics in-vivo non-invasively using ultrasound estimation method with 100 KHz frame rate is proposed. Three models in conjunction with each other are used to study the biomechanics behavior of corneal tissue pre- and post-refractive surgery. These three models are cornea FEM, cornea scatterrer model and ultrasound transducer model respectively. Nine different elastic moduli corneal models are constructed to achieve this goal; 140KPa, 300KPa, 600KPa and 800KPa as post-refractive surgery models and 1MPa, 1.5MPa, 2MPa, 2.5MPa and 3MPa as pre-refractive surgery models respectively. Time-To-Peak (TTP) deformation, deformation amplitude (DA), deformation amplitude ratio at 2 mm (DA ratio 2 mm) and shear wave speed (SWS) are estimated for each of the nine involved corneal models in this study. Results show that TTP is decreasing (6.9 msec. at 140KPa to 5.3 msec. at 3MPa) while increasing the elastic modulus of corneal tissue. Also, DA is decreasing (2 mm at 140KPa to 0.5 mm at 3MPa), while increasing the elastic modulus as well. However, DA ratio shows decrease while increasing of elastic modulus to reflect the difficulty of corneal tissue to deform uniformly at higher elastic moduli. Estimated SWS shows an average accuracy of 98% of the theoretical SWS.
Highlights
Cornea is the transparent component of human ocular system that acts as a protective part enveloping other human ocular components such as lens
We propose a new technique where the same ultrasound transducer is used to generate highly localized acoustic radiation force impulse (ARFI) to act as internal actuator to induce tissue deformation and to perform B-mode imaging procedure to capture the propagation of the deformation wave
The field of view (FOV) is limited to the lateral distance obtained by the ultrasound probe during B-mode imaging
Summary
Cornea is the transparent component of human ocular system that acts as a protective part enveloping other human ocular components such as lens. It preserves shape of human eye and accounts for most of its refractive power [1], [2]. Transparency and uniformity of human cornea are important factors when assessing its role to vision. Human vision degradation is caused by cornea shape alteration due to age, corneal diseases and refractive surgery [1]. Assessing corneal biomechanics post-refractive surgery is of great importance to ophthalmologists [3]–[5]. Refractive surgery outcomes are subjective to corneal biomechanics [6]–[9]
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