Research the Anisotropy Property in Equator Sclera Using High Frequency Ultrasonic Elastography

Abstract

Purpose : Glaucoma is one of the leading causes of blindness across the world, and elevated intraocular pressure is the most risky factor of the glaucoma. The equator sclera plays a pivotal role in vision as it provides stable mechanical support to the fragile optic nerve and retina under dynamic force loading condition. Previous research mainly focused on the mathematical modeling to predict its anisotropy property to the response of elevated IOP. In this study, we aim to use the high frequency ultrasonic array based elastography to investigate the anisotropy property of equator sclera experimentally in the superior, temporal, nasal and inferior locations under different IOP conditions.

Methods : A piezoelectric shaker was used to induce tissue motion instead of acoustic radiation force. The unscalded pig eye was connected with infusion line and IOP sensor. A mechanical shaker (mini-shaker type 4810; Bruel & Kjaer) was positioned at the anterior sclera to initiate elastic wave. An ultrasonic array (L22-14v; Verasonics Inc.) was positioned above the equator sclera and its beam was aligned to be parallel with the shaker.

Results : Fig. 1 shows one example in the superior location of the B-mode images and the corresponding spatial-temporal maps in different IOP in two different directions. The elastic wave speed can be acquired using liner regression algorithm of each wavefront with its corresponding lateral position (indicated by red lines). In the equator direction, from 10 mmHg to 30 mmHg, the elastic wave speed is 6.1 m/s, 11.83 m/s, 13.70 m/s, 14.35 m/s and 15.16 m/s respectively. The reconstructed Young’s modulus is 111.63 KPa, 419.85 KPa, 563.07 KPa, 617.77 KPa and 689.48 KPa respectively. In the anterior to posterior direction, elastic wave velocities are 3.7 m/s, 4.26 m/s, 4.75 m/s, 5.46 m/s and 6.18 m/s, and the Young's modulus are 32.08 KPa, 54.44 KPa, 67.69 KPa, 89.43 KPa, 114.58 KPa correspondingly.

Conclusions : The equator sclera has the anisotropy property, it is stiffer along with the equator direction. These results demonstrate the feasibility of our system to investigate the anisotropy property in equator sclera with elevated IOP.

This is a 2021 ARVO Annual Meeting abstract.

 

Fig 1 B-mode imaging of equator sclera and its corresponding spatial-temporal map in superior position with elevated IOP. a. Equator direction. b. Anterior to posterior direction.