Possible depth-resolved reconstruction of shear moduli in the cornea following collagen crosslinking (CXL) with optical coherence tomography and elastography.

Corneal collagen crosslinking (CXL) is commonly used to prevent or treat keratoconus. Although changes in corneal stiffness induced by CXL surgery can be monitored with non-contact dynamic optical coherence elastography (OCE) by tracking mechanical wave propagation, depth dependent changes are still unclear if the cornea is not crosslinked through the whole depth. Here, phase-decorrelation measurements on optical coherence tomography (OCT) structural images are combined with acoustic micro-tapping (AµT) OCE to explore possible reconstruction of depth-dependent stiffness within crosslinked corneas in an human cornea sample.

Possible depth-resolved reconstruction of shear moduli in the cornea following collagen crosslinking (CXL) with optical coherence tomography and elastography.

Corneal collagen crosslinking (CXL) is commonly used to prevent or treat keratoconus. Although changes in corneal stiffness induced by CXL surgery can be monitored with non-contact dynamic optical coherence elastography (OCE) by tracking mechanical wave propagation, depth dependent changes are still unclear if the cornea is not crosslinked through the whole depth. Here, phase-decorrelation measurements on optical coherence tomography (OCT) structural images are combined with acoustic micro-tapping (A$\mu$T) OCE to explore possible reconstruction of depth-dependent stiffness within crosslinked corneas in an ex vivo human cornea sample.

Noncontact Acoustic Micro-Tapping Optical Coherence Elastography for Quantification of Corneal Anisotropic Elasticity: In Vivo Rabbit Study.

Purpose: The purpose of this study was to demonstrate accurate measurement of corneal elastic moduli in vivo with noncontact and noninvasive optical coherence elastography.

Methods: Elastic properties (in-plane Young's modulus, E, and both in-plane, μ, and out-of-plane, G, shear moduli) of rabbit cornea were quantified in vivo using noncontact dynamic acoustic micro-tapping optical coherence elastography (AµT-OCE). The intraocular pressure (IOP)-dependence of measured mechanical properties was explored in extracted whole globes following in vivo measurement.

Non-contact acoustic micro-tapping optical coherence elastography for quantification of corneal anisotropic elasticity: in vivo rabbit study.

Purpose: To demonstrate accurate measurement of corneal elastic moduli in vivo with non-contact and non-invasive optical coherence elastography.

Methods: Elastic properties (in-plane Young's modulus E and both in-plane, u, and out-of-plane, G, shear moduli) of rabbit cornea were quantified in vivo using non-contact dynamic Acoustic micro-Tapping Optical Coherence Elastography (AuT-OCE). The IOP-dependence of measured mechanical properties was explored in extracted whole globes following in vivo measurement.

Acoustic Micro-Tapping Optical Coherence Elastography to Quantify Corneal Collagen Cross-Linking: An Ex Vivo Human Study.

Purpose: To evaluate changes in the anisotropic elastic properties of ex vivo human cornea treated with ultraviolet cross-linking (CXL) using noncontact acoustic micro-tapping optical coherence elastography (AμT-OCE).

Design: Acoustic micro-tapping OCE was performed on normal and CXL human donor cornea in an ex vivo laboratory study.

Subjects: Normal human donor cornea (n = 22) divided into 4 subgroups.

Delineating Corneal Elastic Anisotropy in a Porcine Model Using Noncontact OCT Elastography and Ex Vivo Mechanical Tests.

Purpose: To compare noncontact acoustic microtapping (AμT) OCT elastography (OCE) with destructive mechanical tests to confirm corneal elastic anisotropy.

Design: Ex vivo laboratory study with noncontact AμT-OCE followed by mechanical rheometry and extensometry.

Participants: Inflated cornea of whole-globe porcine eyes (n = 9).

Spatial resolution in optical coherence elastography of bounded media.

Dynamic optical coherence elastography (OCE) tracks mechanical wave propagation in the subsurface region of tissue to image its shear modulus. For bulk shear waves, the lateral resolution of the reconstructed modulus map (i.e.

The disposable bandage soft contact lenses therapy and anterior segment optical coherence tomography for management of ocular graft-versus-host disease.

Purpose: To identify the ocular surface changes of ocular graft-versus-host disease (GVHD) using anterior segment optical coherence tomography (AS-OCT) and examine the efficacy of disposable bandage soft contact lens (BSCL) treatment in ocular GVHD patients.

Methods: This study is a prospective, Phase II clinical trial. Nineteen patients diagnosed with chronic GVHD based on the NIH criteria and ocular symptoms of NIH eye score 2 or greater were enrolled.

Nearly-incompressible transverse isotropy (NITI) of cornea elasticity: model and experiments with acoustic micro-tapping OCE.

The cornea provides the largest refractive power for the human visual system. Its stiffness, along with intraocular pressure (IOP), are linked to several pathologies, including keratoconus and glaucoma. Although mechanical tests can quantify corneal elasticity ex vivo, they cannot be used clinically.

Super-shear evanescent waves for non-contact elastography of soft tissues.

We describe surface wave propagation in soft elastic media at speeds exceeding the bulk shear wave speed. By linking these waves to the elastodynamic Green's function, we derive a simple relationship to quantify the elasticity of a soft medium from the speed of this supershear evanescent wave (SEW). We experimentally probe SEW propagation in tissue-mimicking phantoms, human cornea , and skin using a high-speed optical coherence elastography system.

Spatial resolution in dynamic optical coherence elastography.

Dynamic optical coherence elastography (OCE) tracks elastic wave propagation speed within tissue, enabling quantitative three-dimensional imaging of the elastic modulus. We show that propagating mechanical waves are mode converted at interfaces, creating a finite region on the order of an acoustic wavelength where there is not a simple one-to-one correspondence between wave speed and elastic modulus. Depending on the details of a boundary’s geometry and elasticity contrast, highly complex propagating fields produced near the boundary can substantially affect both the spatial resolution and contrast of the elasticity image.

Does group velocity always reflect elastic modulus in shear wave elastography?

Dynamic elastography is an attractive method to evaluate tissue biomechanical properties. Recently, it was extended from US- and MR-based modalities to optical ones, such as optical coherence tomography for three-dimensional (3-D) imaging of propagating mechanical waves in subsurface regions of soft tissues, such as the eye. The measured group velocity is often used to convert wave speed maps into 3-D images of the elastic modulus distribution based on the assumption of bulk shear waves.

Modified conjunctival flap as a primary procedure for nontraumatic acute corneal perforation.

Objective: Appropriate management of nontraumatic acute corneal perforation is always a challenge even with the many advances in surgical materials and techniques. We reported the outcomes of a case series of acute corneal perforation repair using a newly modified conjunctival flap with amniotic membrane transplant (AMT), fibrin glue, and a bandage soft contact lens (BCL).

Materials And Methods: A total of 13 consecutive referral cases with nontraumatic acute corneal perforation at the University of Washington were reviewed.

Optical coherence elastography in ophthalmology.

Optical coherence elastography (OCE) can provide clinically valuable information based on local measurements of tissue stiffness. Improved light sources and scanning methods in optical coherence tomography (OCT) have led to rapid growth in systems for high-resolution, quantitative elastography using imaged displacements and strains within soft tissue to infer local mechanical properties. We describe in some detail the physical processes underlying tissue mechanical response based on static and dynamic displacement methods.

Robust numerical phase stabilization for long-range swept-source optical coherence tomography.

A novel phase stabilization technique is demonstrated with significant improvement in the phase stability of a micro-electromechanical (MEMS) vertical cavity surface-emitting laser (VCSEL) based swept-source optical coherence tomography (SS-OCT) system. Without any requirements of hardware modifications, the new fully numerical phase stabilization technique features high tolerance to acquisition jitter, and significantly reduced budget in computational effort. We demonstrate that when measured with biological tissue, this technique enables a phase sensitivity of 89 mrad in highly scattering tissue, with image ranging distance of up to 12.

Acoustic micro-tapping for non-contact 4D imaging of tissue elasticity.

Elastography plays a key role in characterizing soft media such as biological tissue. Although this technology has found widespread use in both clinical diagnostics and basic science research, nearly all methods require direct physical contact with the object of interest and can even be invasive. For a number of applications, such as diagnostic measurements on the anterior segment of the eye, physical contact is not desired and may even be prohibited.

Moving-source elastic wave reconstruction for high-resolution optical coherence elastography.

Optical coherence tomography (OCT)-based elasticity imaging can map soft tissue elasticity based on speckle-tracking of elastic wave propagation using highly sensitive phase measurements of OCT signals. Using a fixed elastic wave source and moving detection, current imaging sequences have difficulty in reconstructing tissue elasticity within speckle-free regions, for example, within the crystalline lens of the eye. We present a moving acoustic radiation force imaging sequence to reconstruct elastic properties within a speckle-free region by tracking elastic wave propagation from multiple laterally moving sources across the field of view.

Air-coupled acoustic radiation force for non-contact generation of broadband mechanical waves in soft media.

A non-contact method for efficient, non-invasive excitation of mechanical waves in soft media is proposed, in which we focus an ultrasound (US) signal through air onto the surface of a medium under study. The US wave reflected from the air/medium interface provides radiation force to the medium surface that launches a transient mechanical wave in the transverse (lateral) direction. The type of mechanical wave is determined by boundary conditions.

Strategies to improve phase-stability of ultrafast swept source optical coherence tomography for single shot imaging of transient mechanical waves at 16 kHz frame rate.

We present single-shot phase-sensitive imaging of propagating mechanical waves within tissue, enabled by an ultrafast optical coherence tomography (OCT) system powered by a 1.628 MHz Fourier domain mode-locked (FDML) swept laser source. We propose a practical strategy for phase-sensitive measurement by comparing the phases between adjacent OCT B-scans, where the B-scan contains a number of A-scans equaling an integer number of FDML buffers.