A fast method to measure the biomechanical properties of human optic nerve head tissues in vivo

Abstract

Purpose : To estimate the biomechanical properties of optic nerve head (ONH) tissues in vivo using optical coherence tomography (OCT) imaging and a fast computational method, namely, the virtual fields method (VFM).

Methods : A healthy human subject (age: 57) was recruited at the Singapore National Eye Centre. The ONH from the right eye was first scanned at baseline intraocular pressure (IOP, measured to be 17 mmHg) using Spectral-domain OCT (Fig1.a). IOP was then gently raised by indenting the anterior sclera through the lower eyelid using an ophthalmodynamometer. While the indenter was maintained in place, IOP was measured to be 39 mmHg with a Tonopen and a second OCT scan of the ONH was acquired. Digital reconstruction of the ONH and 3D tracking algorithms were used to calculate the IOP-induced displacements of the visible prelamina and lamina cribrosa (LC) using established protocols (Fig1.b). Tissue displacements (for the hexahedron-meshed region of interest in Fig1.c) and IOP information were then fed into our VFM algorithm to extract the biomechanical properties of the prelamina and LC (Fig1.d).

Results : For the studied subject’s ONH, the measured elastic moduli of the prelamina and of the LC were 100.3 kPa and 189.1 kPa, respectively, which fell within the range of ex-vivo literature values. The computational time for VFM was 6 seconds using a standard computer (2.9 GHz quad-core Intel Core i5).

Conclusions : We present here novel engineering tools that can extract the biomechanical properties of the prelamina and of the LC in-vivo. The LC was found stiffer than the prelamina, likely due to the presence of collagen. Our proposed VFM method is fast and has potential in identifying patient-specific ONH biomechanical properties in the clinic.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Fig. 1 a) Flowchart for the VFM implementation to extract the biomechanical properties of human ONH tissues. b) Digital reconstruction of the prelamina and LC from the OCT volume of one healthy subject’s ONH. c) The relative position between the region of interest used in VFM (shown in blue) and the segmented ONH geometry (retina/prelamina shown in yellow, LC shown in orange). d) Mesh used in the VFM.