Assessing the Effect of Intraocular Pressure on Elastic Wave Propagation Using Optical Coherence Elastography

Abstract

Purpose : Abnormalities in the mechanical stiffness of corneal tissue as in the cases of fibrosis, keratoconus, or excessive crosslinking can remodel the corneal architecture and significantly impair vision. Optical coherence elastography (OCE) is an emerging imaging technique that has shown potential for the acquisition of high-resolution spatial information of corneal stiffness directly in vivo. Accurate assessment of tissue stiffness, however, relies on a more comprehensive understanding of elastic wave propagation through corneal tissue. Here, we assess the effects of intraocular pressure on the elastic wave propagation and the accuracy of OCE-acquired stiffness measurements.

Methods : An OCE system was custom-built and consisted of a spectral domain-OCT (SD-OCT) coupled with a mechanical piezo actuator. OCT imaging was timed with the mechanical stimulation of the piezo so that elastic wave propagation could be tracked. The raw OCT phase data was processed in MATLAB software. System calibration was performed using phantoms made of gelatin-methacrylate prior to any corneal experiments. Once calibrated, whole porcine globes were used to study elastic wave propagation in ex vivo corneal tissue. The porcine globes were cannulated, and the intraocular pressure (IOP) was controlled using a custom-built apparatus and a pressure sensor. The elastic wave speed was measured at different IOPs. Computational models were constructed using COMSOL software to assess the effect of IOP and tensile prestress on wave propagation.

Results : Preliminary results suggest that IOP has a significant effect on the propagation speed of elastic waves traveling through porcine corneal tissue. Computational models demonstrate that the increase in tensile prestress from higher IOPs increases the wave speed and lowers the accuracy of OCE-based corneal stiffness measurements.

Conclusions : Significant changes in intraocular pressure create tensile prestress within the corneal tissue, resulting in inaccurate measurements of corneal mechanical properties. Our computational model helps to understand and correct the OCE measurements. The development of OCE for clinical application may allow for direct monitoring of corneal stiffness and other mechanical properties during disease progression or after clinical therapies.

This is a 2021 ARVO Annual Meeting abstract.