Optical coherence elastography for strain dynamics measurements in laser correction of cornea shape

Abstract

We describe the use of elastographic processing in phase-sensitive optical coherence tomography (OCT) for visualizing dynamics of strain and tissue-shape changes during laser-induced photothermal corneal reshaping, for applications in the emerging field of non-destructive and non-ablative (non-LASIK) laser vision correction. The proposed phase-processing approach based on fairly sparse data acquisition enabled rapid data processing and near-real-time visualization of dynamic strains. The approach avoids conventional phase unwrapping, yet allows for mapping strains even for significantly supra-wavelength inter-frame displacements of scatterers accompanied by multiple phase-wrapping. These developments bode well for real-time feedback systems for controlling the dynamics of corneal deformation with 10-100 ms temporal resolution, and for suitably long-term monitoring of resultant reshaping of the cornea. In ex-vivo experiments with excised rabbit eyes, we demonstrate temporal plastification of cornea that allows shape changes relevant for vision-correction applications without affecting its transparency. We demonstrate OCT's ability to detect achieving of threshold temperatures required for tissue plastification and simultaneously characterize transient and cumulative strain distributions, surface displacements, and scattering tissue properties. Comparison with previously used methods for studying laser-induced reshaping of cartilaginous tissues and numerical simulations is performed.

Practical obstacles and their mitigation strategies in compressional optical coherence elastography of biological tissues

“…Cumulative strain approach for enhancing SNR in a nonperiodic-deformation scenario makes it possible to signi¯cantly extend the range of visualized strains to a several percent level (and even greater 34,35 ), compared to sub-percentage levels common in interframe phase-resolved measurements. 29 Such an extended strain range opens the possibility to study possible deviation of the tissue response from the linear Hooke's law (assumed in Eq.…”

Anterior segment optical coherence tomography and its clinical applications

“…AS‐OCT technology is now able to transcend the anatomical assessment of the AS to physiological properties such as ocular tissue biomechanics. OCT elastography has been used by Kirby et al and Zaitsev et al to analyse tissue movement and velocity in response to forces, such as in laser corneal reshaping …”

Photoacoustic elastography imaging: a review

“…Furthermore, an estimate of a single small-strain value of Young's modulus, obtaining from nonlinear stress-strain curves, has also been successfully demonstrated by several groups. Several dynamic methods, 33 which differ significantly from previously discussed variants, came into existence. Compressional OCE, which was originally proposed (in 1998) by Schmitt,22 has been adopted by several groups in recent years and there have been significant advances in aspects of signal processing and analysis.…”