1. Articles from René M. Werkmeister

    1-18 of 18
    1. Ultrahigh‐resolution anterior segment optical coherence tomography for analysis of corneal microarchitecture during wound healing

      Ultrahigh‐resolution anterior segment optical coherence tomography for analysis of corneal microarchitecture during wound healing

      Purpose To employ ultrahigh‐resolution (UHR) optical coherence tomography (OCT) for investigation of the early wound healing process in corneal epithelium. Methods A custom‐built UHR‐OCT system assessed epithelial healing in human keratoconic cornea after epi‐off crosslinking (CXL) procedure and a wound healing model in rabbits with iatrogenic corneal injury. 3D OCT data sets enhanced obtaining epithelial thickness maps and evaluation of reepithelization stage. Accompanying changes in deeper corneal microarchitecture were analysed. Results The mean central corneal thickness in 40 eyes with keratoconus at baseline was 482.7 ± 38.2 μ m, while mean central epithelial thickness (CET) was ...

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    2. In Vivo Characterization of Spontaneous Retinal Neovascularization in the Mouse Eye by Multifunctional Optical Coherence Tomography

      In Vivo Characterization of Spontaneous Retinal Neovascularization in the Mouse Eye by Multifunctional Optical Coherence Tomography

      Purpose : To investigate the early development of spontaneous retinal neovascularization in the murine retina by a multifunctional optical coherence tomography approach. To characterize involved tissue changes in vivo and describe structural and functional changes over time. Methods : A multifunctional optical coherence tomography (OCT) system providing 3-fold contrast comprising reflectivity, polarization sensitivity, and OCT angiography (OCTA) was utilized to image very-low-density lipoprotein receptor (VLDLR) knockout mice. Baseline measurements were acquired as early as postnatal day 14 and a follow-up of neovascularization development was performed until the age of 3 months. Control mice were imaged accordingly and a multiparametric image analysis was ...

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    3. Ultrahigh-resolution OCT imaging of the human cornea

      Ultrahigh-resolution OCT imaging of the human cornea

      We present imaging of corneal pathologies using optical coherence tomography (OCT) with high resolution. To this end, an ultrahigh-resolution spectral domain OCT (UHR-OCT) system based on a broad bandwidth Ti:sapphire laser is employed. With a central wavelength of 800 nm, the imaging device allows to acquire OCT data at the central, paracentral and peripheral cornea as well as the limbal region with 1.2 µm x 20 µm (axial x lateral) resolution at a rate of 140 000 A-scans/s. Structures of the anterior segment of the eye, not accessible with commercial OCT systems, are visualized. These include corneal ...

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    4. Effect of different lubricant eye gels on tear film thickness as measured with ultrahigh-resolution optical coherence tomography

      Effect of different lubricant eye gels on tear film thickness as measured with ultrahigh-resolution optical coherence tomography

      Purpose To compare the effect of a single drop of different lubricant eye gels on tear film thickness (TFT) as measured with ultrahigh-resolution optical coherence tomography (UHR-OCT) in patients with mild-to-moderate dry eye disease (DED). Methods The study followed a randomized, single-masked, observer-blinded parallel group design. Patients received a single dose of either unpreserved trehalose 3% + hyaluronic acid 0.15% (TH), hyaluronic acid 0.2% (HA) or polyethylene glycol 0.4% + propylene glycol 0.3% (PP) eye drops. In total, 60 patients were included and TFT was measured using a custom-built UHR-OCT system. Results The mean TFT at baseline was ...

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    5. Measurement of Retinal Vascular Caliber From Optical Coherence Tomography Phase Images

      Measurement of Retinal Vascular Caliber From Optical Coherence Tomography Phase Images

      Purpose : To compare retinal vessel calibers extracted from phase-sensitive optical coherence tomography (OCT) images with vessel calibers as obtained from the Retinal Vessel Analyzer (RVA). Methods : Data from previously published studies in 13 healthy subjects breathing room air ( n = 214 vessels) and 7 subjects breathing 100% oxygen ( n = 101 vessels) were used. Vessel calibers from OCT phase images were measured vertically along the optical axis by three independent graders. The data from RVA fundus images were corrected for magnification to obtain absolute values. Results : The average vessel diameter as obtained from OCT images during normoxia was lower than from RVA ...

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    6. Total Retinal Blood Flow in a Nonhuman Primate Optic Nerve Transection Model Using Dual-Beam Bidirectional Doppler FD-OCT and Microsphere Method

      Total Retinal Blood Flow in a Nonhuman Primate Optic Nerve Transection Model Using Dual-Beam Bidirectional Doppler FD-OCT and Microsphere Method

      Purpose : We validated noninvasive Doppler-optical coherence tomography (OCT) blood flow measurements against the terminal microsphere method in a surgical induced optic nerve transection nonhuman primate model. Methods : In 6 nonhuman primates, total retinal blood flow (TRBF) was measured with a custom-built dual-beam bidirectional Doppler Fourier Domain (FD)-OCT. Peripapillary retinal nerve fiber layer thickness (RNFLT) was measured by Spectralis spectral-domain (SD)-OCT. Measurements were performed every 10 to 15 days before and after unilateral optic nerve transection (ONT) until RNFLT was reduced by more than 40% from baseline. Before the animals were killed, TRBF was measured using the microsphere technique ...

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    7. In vivo tear film thickness measurement and tear film dynamics visualization using spectral domain optical coherence tomography

      In vivo tear film thickness measurement and tear film dynamics visualization using spectral domain optical coherence tomography

      Dry eye syndrome is a highly prevalent disease of the ocular surface characterized by an instability of the tear film. Traditional methods used for the evaluation of tear film stability are invasive or show limited repeatability. Here we propose a new non-invasive fully automated approach to measure tear film thickness based on spectral domain optical coherence tomography and on an efficient delay estimator. Silicon wafer phantom were used to validate the thickness measurement. The technique was applied in vivo in healthy subjects. Series of tear film thickness maps were generated, allowing for the visualization of tear film dynamics. Our results ...

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    8. Blood flow velocity vector field reconstruction from dual-beam bidirectional Doppler OCT measurements in retinal veins

      Blood flow velocity vector field reconstruction from dual-beam bidirectional Doppler OCT measurements in retinal veins

      In this paper, we demonstrate the possibility to reconstruct the actual blood flow velocity vector field in retinal microvessels from dual-beam bidirectional Doppler optical coherence tomography measurements. First, for a better understanding of measured phase patterns, several flow situations were simulated on the basis of the known dual beam measurement geometry. We were able to extract the vector field parameters that determine the measured phase pattern, allowing for the development of an algorithm to reconstruct the velocity vector field from measured phase data. In a next step, measurements were performed at a straight vessel section and at a venous convergence ...

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    9. Line-field parallel swept source MHz OCT for structural and functional retinal imaging

      Line-field parallel swept source MHz OCT for structural and functional retinal imaging

      We demonstrate three-dimensional structural and functional retinal imaging with line-field parallel swept source imaging (LPSI) at acquisition speeds of up to 1 MHz equivalent A-scan rate with sensitivity better than 93.5 dB at a central wavelength of 840 nm. The results demonstrate competitive sensitivity, speed, image contrast and penetration depth when compared to conventional point scanning OCT. LPSI allows high-speed retinal imaging of function and morphology with commercially available components. We further demonstrate a method that mitigates the effect of the lateral Gaussian intensity distribution across the line focus and demonstrate and discuss the feasibility of high-speed optical angiography ...

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    10. Effect of hyaluronic acid on tear film thickness as assessed with ultra-high resolution optical coherence tomography

      Effect of hyaluronic acid on tear film thickness as assessed with ultra-high resolution optical coherence tomography

      Purpose The aim of this study was to assess the effect of a single drop of hyaluronic acid on tear film thickness (TFT) in healthy subjects. Methods Sixteen healthy subjects (eight male/eight female) aged between 20 and 36 years were included in this randomized, double-masked placebo-controlled study. One eye received a single dose of hyaluronic acid (Olixia pure ® ; Croma Pharma, Korneuburg, Austria) eye drops, and the fellow eye received physiologic saline solution as placebo control. The study eye was chosen randomly. TFT as measured with a custom-built Fourier-domain optical coherence tomography (FD-OCT) system was the main outcome variable and ...

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    11. Measurement of retinal blood flow in the rat by combining Doppler Fourier-domain optical coherence tomography with fundus imaging

      Measurement of retinal blood flow in the rat by combining Doppler Fourier-domain optical coherence tomography with fundus imaging

      A wide variety of ocular diseases are associated with abnormalities in ocular circulation. As such, there is considerable interest in techniques for quantifying retinal blood flow, among which Doppler optical coherence tomography (OCT) may be the most promising. We present an approach to measure retinal blood flow in the rat using a new optical system that combines the measurement of blood flow velocities via Doppler Fourier-domain optical coherence tomography and the measurement of vessel diameters using a fundus camera-based technique. Relying on fundus images for extraction of retinal vessel diameters instead of OCT images improves the reliability of the technique ...

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    12. Doppler Optical Coherence Tomography

      Doppler Optical Coherence Tomography

      Optical Coherence Tomography (OCT) has revolutionized ophthalmology. Since its introduction in the early 1990s it has continuously improved in terms of speed, resolution and sensitivity. The technique has also seen a variety of extensions aiming to assess functional aspects of the tissue in addition to morphology. One of these approaches is Doppler OCT (DOCT), which aims to visualize and quantify blood flow. Such extensions were already implemented in time domain systems, but have gained importance with the introduction of Fourier domain OCT. Nowadays phase-sensitive detection techniques are most widely used to extract blood velocity and blood flow from tissues. A ...

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    13. Measurement of the total retinal blood flow using dual beam Fourier-domain Doppler optical coherence tomography with orthogonal detection planes

      Measurement of the total retinal blood flow using dual beam Fourier-domain Doppler optical coherence tomography with orthogonal detection planes

      We present a system capable of measuring the total retinal blood flow using a combination of dual beam Fourier-domain Doppler optical coherence tomography with orthogonal detection planes and a fundus camera-based retinal vessel analyzer. Our results show a high degree of conformity of venous and arterial flows, which corroborates the validity of the measurements. In accordance with Murray’s law, the log-log regression coefficient between vessel diameter and blood flow was found to be ~3. The blood’s velocity scaled linearly with the vessel diameter at higher diameters (> 60 µm), but showed a clear divergence from the linear dependence at ...

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    14. In vitro and in vivo three-dimensional velocity vector measurement by three-beam spectral-domain Doppler optical coherence tomography

      In vitro and in vivo three-dimensional velocity vector measurement by three-beam spectral-domain Doppler optical coherence tomography

      We developed a three-beam Doppler optical coherence tomography (OCT) system that enables measurement of the velocity vector of moving particles in three-dimensions (3-D). The spatial orientation as well as the magnitude of motion can be determined without prior knowledge of the geometry of motion. The system combines three spectral-domain OCT interferometers whose sample beams are focused at the sample by a common focusing lens at three different angles. This provides three spatially independent velocity components simultaneously from which the velocity vector can be reconstructed. We demonstrate the system in a simple test object (rotating disc), a flow phantom, and for ...

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    15. Dove prism based rotating dual beam bidirectional Doppler OCT

      Dove prism based rotating dual beam bidirectional Doppler OCT

      Traditional Doppler OCT is highly sensitive to motion artifacts due to the dependence on the Doppler angle. This limits its accuracy in clinical practice. To overcome this limitation, we use a bidirectional dual beam technique equipped with a novel rotating scanning scheme employing a Dove prism. The volume is probed from two distinct illumination directions with variable controlled incidence plane, allowing for reconstruction of the true flow velocity at arbitrary vessel orientations. The principle is implemented with Swept Source OCT at 1060nm with 100,000 A-Scans/s. We apply the system to resolve pulsatile retinal absolute blood velocity by performing ...

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    16. Measurement of Absolute Blood Flow Velocity and Blood Flow in the Human Retina by Dual-beam Bidirectional Doppler Fourier-Domain Optical Coherence Tomography

      Measurement of Absolute Blood Flow Velocity and Blood Flow in the Human Retina by Dual-beam Bidirectional Doppler Fourier-Domain Optical Coherence Tomography

      Purpose The present experiments were undertaken to evaluate the validity of absolute flow velocity measurements using a dual-beam bidirectional Doppler Fourier-domain optical coherence tomography (FD-OCT) system. Methods The flow velocities of diluted milk through a glass capillary were measured at 30 different preset velocities in the range of 0.9 to 39.3 mm/s by bidirectional Doppler FD-OCT. The flow through the capillary was controlled by two infusion pumps working in different flow ranges and based on different technical principles. In vivo the validity of the method for measuring blood flow in retinal vessels was tested at bifurcations. The ...

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    17. In vivo bi-directional Doppler Fourier-domain optical coherence tomography for measurement of absolute flow velocities

      A bidirectional FDOCT system capable of measuring absolute velocities of moving scatterers is described. In this setup the sample is illuminated with two differently polarized beams. These two probe beams impinging onto the sample at a known angle. The velocity estimation is independent of the exact direction of the velocity vector in the detection plane. Evaluation measurements were performed on a rotating disc driven at well defined velocities and tilted by various small angles around to /2. Our results indicate a high correlation between pre-set and estimated velocities and the independency of these velocities from the tilting angle of the ...
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    18. Bidirectional Doppler Fourier-domain optical coherence tomography for measurement of absolute flow velocities in human retinal vessels

      Bidirectional Doppler Fourier-domain optical coherence tomography for measurement of absolute flow velocities in human retinal vessels
      We describe a bidirectional color Doppler Fourier-domain optical coherence tomography system capable of measuring absolute velocities of moving scatterers by illuminating the sample with two linearly and orthogonally polarized beams, incident at a known angle on the sample. The velocity calculation is independent of the exact orientation of the velocity vector in the detection plane. First measurements were performed on a rotating disk driven at well-defined velocities and tilted by various small angles. Our results indicate a high correlation between preset and calculated velocities (correlation coefficient 0.999) and the independency of these velocities from the tilting angle of the ...
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    1-18 of 18
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  2. Topics in the News

    1. (16 articles) Medical University of Vienna
    2. (9 articles) Rainer A. Leitgeb
    3. (4 articles) Christoph K. Hitzenberger
    4. (3 articles) Michael Pircher
    5. (3 articles) Angelika Unterhuber
    6. (3 articles) Cedric Blatter
    7. (2 articles) Erich Götzinger
    8. (2 articles) Bernhard Baumann
    9. (2 articles) Branislav Grajciar
    10. (1 articles) Devers Eye Institute
    11. (1 articles) L V Prasad Eye Institute
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    Bidirectional Doppler Fourier-domain optical coherence tomography for measurement of absolute flow velocities in human retinal vessels Measurement of Absolute Blood Flow Velocity and Blood Flow in the Human Retina by Dual-beam Bidirectional Doppler Fourier-Domain Optical Coherence Tomography Dove prism based rotating dual beam bidirectional Doppler OCT In vitro and in vivo three-dimensional velocity vector measurement by three-beam spectral-domain Doppler optical coherence tomography Measurement of the total retinal blood flow using dual beam Fourier-domain Doppler optical coherence tomography with orthogonal detection planes Doppler Optical Coherence Tomography Measurement of retinal blood flow in the rat by combining Doppler Fourier-domain optical coherence tomography with fundus imaging Line-field parallel swept source MHz OCT for structural and functional retinal imaging Blood flow velocity vector field reconstruction from dual-beam bidirectional Doppler OCT measurements in retinal veins Optical coherence tomography angiography of foveal neovascularisation in proliferative diabetic retinopathy Treating port wine stain birthmarks using dynamic optical coherence tomography-guided setting Repeatability of quantitative measurements of retinal layers with SD-OCT and agreement between vertical and horizontal scan protocols in healthy eyes