1. Michael D. Twa

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    1. Mentioned In 30 Articles

    2. In Vivo Human Corneal Shear-wave Optical Coherence Elastography

      In Vivo Human Corneal Shear-wave Optical Coherence Elastography
      SIGNIFICANCE A novel imaging technology, dynamic optical coherence elastography (OCE), was adapted for clinical noninvasive measurements of corneal biomechanics. PURPOSE Determining corneal biomechanical properties is a long-standing challenge. Elasticity imaging methods have recently been developed and applied for clinical evaluation of soft tissues in cancer detection, atherosclerotic plaque evaluation, surgical guidance, and more. Here, we describe the use of dynamic OCE to characterize mechanical wave propagation in the human cornea ...
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    3. Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics

      Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics
      We present an air-coupled ultrasonic radiation force probe co-focused with a phase-sensitive optical coherence tomography (OCT) system for quantitative wave-based elastography. A custom-made 1 MHz spherically focused piezoelectric transducer with a concentric 10 mm wide circular opening allowed for confocal micro-excitation of waves and phase-sensitive OCT imaging.
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    4. Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus

      Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus
      Purpose : Currently, the biomechanical properties of the corneo-scleral limbus when the eye-globe deforms are largely unknown. The purpose of this study is to evaluate changes in elasticity of the cornea, sclera, and limbus when subjected to different intraocular pressures (IOP) using wave-based optical coherence elastography (OCE). Special attention was given to the elasticity changes of the limbal region with respect to the elasticity variations in the neighboring corneal and scleral ...
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    5. Clinical Corneal Optical Coherence Elastography Measurement Precision: Effect of Heartbeat and Respiration

      Clinical Corneal Optical Coherence Elastography Measurement Precision: Effect of Heartbeat and Respiration
      Purpose : Normal physiological movements (e.g., respiration and heartbeat) induce eye motions during clinical measurements of human corneal biomechanical properties using optical coherence elastography (OCE). We quantified the effects of respiratory and cardiac-induced eye motions on clinical corneal OCE measurement precision and repeatability. Methods : Corneal OCE was performed using low-force, micro-air-pulse tissue stimulation and high-resolution phase-sensitive optical coherence tomography (OCT) imaging. Axial surface displacements of the corneal apex were measured ...
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    6. Fernando Zvietcovich awarded SPIE-Franz Hillenkamp Postdoctoral Fellowship

      Fernando Zvietcovich awarded SPIE-Franz Hillenkamp Postdoctoral Fellowship
      The 2020 award will support research into optical coherence elastography and its translation into clinics. Fernando Zvietcovich, Fellowship recipient The 2020 SPIE-Franz Hillenkamp Postdoctoral Fellowship will be awarded to Fernando Zvietcovich, currently a PhD candidate at the University of Rochester , who will receive the Fellowship's $75,000 prize. This annual award is intended to support interdisciplinary research in the biophotonics sector, and provide opportunities for translating new technologies into ...
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    7. Theory and design of Schwarzschild scan objective for Optical Coherence Tomography

      Theory and design of Schwarzschild scan objective for Optical Coherence Tomography
      Optical coherence elastography (OCE) is one form of multi-channel imaging that combines high-resolution optical coherence tomography (OCT) imaging with mechanical tissue stimulation. This combination of structural and functional imaging can require additional space to integrate imaging capabilities with additional functional elements (e.g., optical, mechanical, or acoustic modulators) either at or near the imaging axis. We address this challenge by designing a novel scan lens based on a modified Schwarzchild ...
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    8. Modified wavelength scanning interferometry for simultaneous tomography and topography of the cornea with Fourier domain optical coherence tomography

      Modified wavelength scanning interferometry for simultaneous tomography and topography of the cornea with Fourier domain optical coherence tomography
      Visual acuity is dependent on corneal shape and size. A minor variation in surface geometry can cause a deformation of corneal geometry, which affects its optical performance. In this work we demonstrate an algorithm for the simultaneous measurement of corneal tomography and topography with a traditional point-scanning Fourier domain optical coherence tomography (FD-OCT) system. A modified wavelength scanning interferometry (mWSI) algorithm enabled topographical evaluation of the surface with nanometer-scale resolution ...
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    9. Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography

      Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography
      Purpose To quantify the effects of the hydration state on the Young's modulus of the cornea . Setting Biomedical Optics Laboratory, University of Houston, Houston, Texas, USA. Design Experimental study. Methods Noncontact, dynamic optical coherence elastography (OCE) measurements were taken of in situ rabbit corneas in the whole eyeglobe configuration (n = 10) and at an artificially controlled intraocular pressure of 15 mm Hg. Baseline OCE measurements were taken by topically ...
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    10. Effects of Thickness on Corneal Biomechanical Properties Using Optical Coherence Elastography

      Effects of Thickness on Corneal Biomechanical Properties Using Optical Coherence Elastography
      SIGNIFICANCE Measured corneal biomechanical properties are driven by intraocular pressure, tissue thickness, and inherent material properties. We demonstrate tissue thickness as an important factor in the measurement of corneal biomechanics that can confound short-term effects due to UV riboflavin cross-linking (CXL) treatment. PURPOSE We isolate the effects of tissue thickness on the measured corneal biomechanical properties using optical coherence elastography by experimentally altering the tissue hydration state and stiffness. METHODS ...
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    11. Common-path phase-sensitive optical coherence tomography provides enhanced phase stability and detection sensitivity for dynamic elastography

      Common-path phase-sensitive optical coherence tomography provides enhanced phase stability and detection sensitivity for dynamic elastography
      Phase-sensitive optical coherence elastography (PhS-OCE) is an emerging optical technique to quantify soft-tissue biomechanical properties. We implemented a common-path OCT design to enhance displacement sensitivity and optical phase stability for dynamic elastography imaging. The background phase stability was greater in common-path PhS-OCE (0.24 0.07nm) than conventional PhS-OCE (1.60 0.11m). The coefficient of variation for surface displacement measurements using conventional PhS-OCE averaged 11% versus 2% for common-path ...
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    12. Quantifying the effects of UV-A/riboflavin crosslinking on the elastic anisotropy and hysteresis of the porcine cornea by noncontact optical coherence elastography

      Quantifying the effects of UV-A/riboflavin crosslinking on the elastic anisotropy and hysteresis of the porcine cornea by noncontact optical coherence elastography
      The collagen fibril orientation of the cornea can provide critical information about cornea tissue health because diseases such as keratoconus and therapeutic interventions such as UV-A/riboflavin corneal collagen crosslinking (CXL) can alter the ultrastructural arrangement of collagen fibrils. Here, we quantify the elastic anisotropy and hysteresis of in situ porcine corneas as a function of intraocular pressure (IOP) with noncontact optical coherence elastography. Moreover, the effects of UV-A riboflavin ...
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    13. Applanation optical coherence elastography: noncontact measurement of intraocular pressure, corneal biomechanical properties, and corneal geometry with a single instrument

      Applanation optical coherence elastography: noncontact measurement of intraocular pressure, corneal biomechanical properties, and corneal geometry with a single instrument
      Current clinical tools provide critical information about ocular health such as intraocular pressure (IOP). However, they lack the ability to quantify tissue material properties, which are potent markers for ocular tissue health and integrity. We describe a single instrument to measure the eye-globe IOP, quantify corneal biomechanical properties, and measure corneal geometry with a technique termed applanation optical coherence elastography (Appl-OCE). An ultrafast OCT system enabled visualization of corneal dynamics ...
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    14. How Will Optometry Respond to Technological Evolution?

      How Will Optometry Respond to Technological Evolution?
      I recently visited the Computer History Museum in Mountain View, California, in the heart of Silicon Valley. This museum chronicles the evolution of computing technology from slide rules to self-driving cars. Their exhibits showcase fascinating stories of what the power of the human mind can achieve. The tangible manifestations of these achievements on display played important parts in ending wars (the ENIGMA cipher machine or the Manhattan Project), walking on ...
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      Mentions: Michael D. Twa
    15. Assessing the effects of riboflavin/UV-A crosslinking on porcine corneal mechanical anisotropy with optical coherence elastography

      Assessing the effects of riboflavin/UV-A crosslinking on porcine corneal mechanical anisotropy with optical coherence elastography
      In this work we utilize optical coherence elastography (OCE) to assess the effects of UV-A/riboflavin corneal collagen crosslinking (CXL) on the mechanical anisotropy of in situ porcine corneas at various intraocular pressures (IOP). There was a distinct meridian of increased Youngs modulus in all samples, and the mechanical anisotropy increased as a function of IOP and also after CXL. The presented noncontact OCE technique was able to quantify the ...
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    16. Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model

      Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model
      The biomechanical properties of the cornea play a critical role in forming vision. Diseases such as keratoconus can structurally degenerate the cornea causing a pathological loss in visual acuity. UV-A/riboflavin corneal collagen crosslinking (CXL) is a clinically available treatment to stiffen the cornea and restore its healthy shape and function. However, current CXL techniques do not account for pre-existing biomechanical properties of the cornea nor the effects of the ...
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  2. About Michael D. Twa

    Michael D. Twa

    Michael D. Twa is at the University of Houston.