Optical Coherence Elastography for Evaluating the Biomechanics of In Vivo Posterior Eye with Elevated IOP

Abstract

Purpose : Glaucoma is one of the leading diseases for blindness across the world. It damages the retinal ganglion cell (RGC) while retina plays a pivotal role in the visual neuropathy. Evidence shows that elevated intraocular pressure (IOP) is the most risk factor for this disease. Currently there is limited research in evaluating the biomechanics of retina since retina locates in the posterior segment as well as it gains a delicate structure. We propose to utilize our optical coherence elastography to investigate the biomechanics of retina. A shaker was used to induce tissue vibration instead of utilizing ultrasound, our system has the potential to be applied in clinic.

Methods : A custom-built OCE system combining a shaker and a spectral-domain optical coherence tomography (SD-OCT) was used for this application. The rabbit was first anesthetized and positioned, and a shaker tip was contacted to the limbus. Then an infusion line and IOP sensor was inserted into the posterior of the eye with trocars. The height of infusion line was controllable to elevate the IOP. To capture the elastic wave propagation with fine image quality, the acquisition speed was set to 30 KHz and 400 A-lines in one positon. 500 points of M-mode frames were acquired similarly with a step size of 6 µm. Raw data was saved to disk for further analysis. Group velocity was then calculated to reconstruct the Young’s modulus using equation E = 3*ρ*C²where E, ρ and C is Young’s modulus, retina density and group velocity respectively.

Results : Retina exhibits five layers in general, from anterior to posterior, they are optic nerve fibers (ONF) & ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL) & outer plexiform layer (OPL), outer nuclear layer (ONL) and photoreceptor (PR). Four IOP readings were chosen from 10 mmHg to 25 mmHg with 5 mmHg interval. Since PR layer was adjunct to sclera, elastic wave attenuated quickly and failed in quantification of this layer. Results of other layers are shown below:

Conclusions : We have shown that our system has the ability to differentiate Young’s modulus in most layers of retina with elevated IOP. Further experiment will be conducted to gain a statistical meaning. Besides changing of biomechanics with elevated IOP in retina, it is also crucial to explore other responses in retina with progression of IOP elevation such as blood flow volume and velocity.

This is a 2020 ARVO Annual Meeting abstract.