1. Articles from Ryan P. McNabb

    1-24 of 24
    1. In Vivo Quantitative Analysis of Anterior Chamber White Blood Cell Mixture Composition Using Spectroscopic Optical Coherence Tomography

      In Vivo Quantitative Analysis of Anterior Chamber White Blood Cell Mixture Composition Using Spectroscopic Optical Coherence Tomography

      Anterior uveitis is the most common form of intraocular inflammation, and one of its main signs is the presence of white blood cells (WBCs) in the anterior chamber (AC). Clinically, the true composition of cells can currently only be obtained using AC paracentesis, an invasive procedure to obtain AC fluid requiring needle insertion into the AC. We previously developed a spectroscopic optical coherence tomography (SOCT) analysis method to differentiate between populations of RBCs and subtypes of WBCs, including granulocytes, lymphocytes and monocytes, both in vitro and in ACs of excised porcine eyes. We have shown that different types of WBCs ...

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    2. Topography and pachymetry maps for mouse corneas using optical coherence tomography

      Topography and pachymetry maps for mouse corneas using optical coherence tomography

      The majority of the eye's refractive power lies in the cornea, and pathological changes in its shape can affect vision. Small animal models offer an unparalleled degree of control over genetic and environmental factors that can help elucidate mechanisms of diseases affecting corneal shape. However, there is not currently a method to characterize the corneal shape of small animal eyes with topography or pachymetry maps, as is done clinically for humans. We bridge this gap by demonstrating methods using optical coherence tomography (OCT) to generate the first topography and pachymetry (thickness) maps of mouse corneas. Radii of curvature acquired ...

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    3. Ocular anterior chamber blood cell population differentiation using spectroscopic optical coherence tomography

      Ocular anterior chamber blood cell population differentiation using spectroscopic optical coherence tomography

      There is potential clinical significance in identifying cellular responses in the anterior chamber (AC) of the eye, which can indicate hyphema (an accumulation of red blood cells [RBCs]) or aberrant intraocular inflammation (an accumulation of white blood cells [WBCs]). In this work, we developed a spectroscopic OCT analysis method to differentiate between populations of RBCs and subtypes of WBCs, including granulocytes, lymphocytes and monocytes, both in vitro and in ACs of porcine eyes. We developed an algorithm to track single cells within OCT data sets, and extracted the backscatter reflectance spectrum of each single cell from the detected interferograms using ...

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    4. Advances in Whole-Eye Optical Coherence Tomography Imaging

      Advances in Whole-Eye Optical Coherence Tomography Imaging

      Contemporary anterior segment and retinal optical coherence tomography (OCT) systems only image their particular designated region of the eye and cannot image both areas of the eye at once. This separation is due to the differences in optical system design needed to properly image the front or back of the eye and also due to limitations in the imaging depth of current commercial OCT systems. More recently, research and commercial OCT systems capable of "whole-eye" imaging have been described. These whole-eye OCT systems enable applications such as ocular biometry for cataract surgery, ocular shape analysis for myopia, and others. Further ...

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    5. Volumetric Measurement of Subretinal Blebs Using Microscope-Integrated Optical Coherence Tomography

      Volumetric Measurement of Subretinal Blebs Using Microscope-Integrated Optical Coherence Tomography

      Purpose : We advance studies of subretinal treatments by developing a microscope-integrated optical coherence tomography (MIOCT) image-based method for measuring the volume of therapeutics delivered into the subretinal space. Methods : A MIOCT image-based volume measurement method was developed and assessed for accuracy and reproducibility by imaging an object of known size in model eyes. This method then was applied to subretinal blebs created by injection of diluted triamcinolone. Bleb volumes obtained from MIOCT were compared to the intended injection volume and the surgeon's estimation of leakage. Results : Validation of the image-based volume measurement method showed accuracy to ±1.0 μL ...

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    6. Anterior chamber blood cell differentiation using spectroscopic optical coherence tomography

      Anterior chamber blood cell differentiation using spectroscopic optical coherence tomography

      There is great clinical importance in identifying cellular responses in the anterior chamber (AC) which can indicate signs of hyphema (an accumulation of red blood cells (RBCs)) or aberrant intraocular inflammation (an accumulation of white blood cells (WBCs)). These responses are difficult to diagnose and require specialized equipment such as ophthalmic microscopes and specialists trained in examining the eye. In this work, we applied spectroscopic OCT to differentiate between RBCs and subtypes of WBCs, including neutrophils, lymphocytes and monocytes, both in vitro and in ACs of porcine eyes. We located and tracked single cells in OCT volumetric images, and extracted ...

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    7. Retinal imaging in human autopsy eyes using a custom optical coherence tomography periscope

      Retinal imaging in human autopsy eyes using a custom optical coherence tomography periscope

      Age-related macular degeneration (AMD) is a major cause of vision loss in the elderly. To better study the pathobiology of AMD, postmortem eyes offer an excellent opportunity to correlate optical coherence tomography (OCT) imaging characteristics with histopathology. However, postmortem eyes from autopsy present challenges to standard OCT imaging including opaque anterior segment structures and standard of care autopsy processing resulting in oblique views to the macula. To overcome these challenges, we report a custom periscope attached by a standard mount to an OCT sample arm and demonstrate high quality macular OCT acquisitions in autopsy-processed eyes.

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    8. Segmentation guided registration of wide field-of-view retinal optical coherence tomography volumes

      Segmentation guided registration of wide field-of-view retinal optical coherence tomography volumes

      Patient motion artifacts are often visible in densely sampled or large wide field-of-view (FOV) retinal optical coherence tomography (OCT) volumes. A popular strategy for reducing motion artifacts is to capture two orthogonally oriented volumetric scans. However, due to larger volume sizes, longer acquisition times, and corresponding larger motion artifacts, the registration of wide FOV scans remains a challenging problem. In particular, gaps in data acquisition due to eye motion, such as saccades, can be significant and their modeling becomes critical for successful registration. In this article, we develop a complete computational pipeline for the automatic motion correction and accurate registration ...

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    9. Method for single illumination source combined optical coherence tomography and fluorescence imaging of fluorescently labeled ocular structures in transgenic mice

      Method for single illumination source combined optical coherence tomography and fluorescence imaging of fluorescently labeled ocular structures in transgenic mice

      In vivo imaging permits longitudinal study of ocular disease processes in the same animal over time. Two different in vivo optical imaging modalities – optical coherence tomography (OCT) and fluorescence – provide important structural and cellular data respectively about disease processes. In this Methods in Eye Research article, we describe and demonstrate the combination of these two modalities producing a truly simultaneous OCT and fluorescence imaging system for imaging of fluorescently labeled animal models. This system uses only a single light source to illuminate both modalities, and both share the same field of view. This allows simultaneous acquisition of OCT and fluorescence ...

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    10. Posterior Eye Shape Measurement With Retinal OCT Compared to MRI

      Posterior Eye Shape Measurement With Retinal OCT Compared to MRI

      Purpose : Posterior eye shape assessment by magnetic resonance imaging (MRI) is used to study myopia. We tested the hypothesis that optical coherence tomography (OCT), as an alternative, could measure posterior eye shape similarly to MRI. Methods : Macular spectral-domain OCT and brain MRI images previously acquired as part of the Singapore Epidemiology of Eye Diseases study were analyzed. The right eye in the MRI and OCT images was automatically segmented. Optical coherence tomography segmentations were corrected for optical and display distortions requiring biometry data. The segmentations were fitted to spheres and ellipsoids to obtain the posterior eye radius of curvature ( R ...

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    11. Wide field of view swept-source optical coherence tomography for peripheral retinal disease

      Wide field of view swept-source optical coherence tomography for peripheral retinal disease

      Background/aims To assess peripheral retinal lesions and the posterior pole in single widefield optical coherence tomography (OCT) volumes. Methods A wide field of view (FOV) swept-source OCT (WFOV SSOCT) system was developed using a commercial swept-source laser and a custom sample arm consisting of two indirect ophthalmic lenses. Twenty-seven subjects with peripheral lesions (choroidal melanomas, choroidal naevi, sclerochoroidal calcification, retinitis pigmentosa, diabetic retinopathy, retinoschisis and uveitis) were imaged with the WFOV SSOCT. Volumes were taken in primary gaze. Using the optic nerve to fovea distance as a reference measurement, comparisons were made between the lateral FOV of the WFOV ...

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    12. Complete 360° circumferential gonioscopic optical coherence tomography imaging of the iridocorneal angle

      Complete 360° circumferential gonioscopic optical coherence tomography imaging of the iridocorneal angle

      Clinically, gonioscopy is used to provide en face views of the ocular angle. The angle has been imaged with optical coherence tomography (OCT) through the corneoscleral limbus but is currently unable to image the angle from within the ocular anterior chamber. We developed a novel gonioscopic OCT system that images the angle circumferentially from inside the eye through a custom, radially symmetric, gonioscopic contact lens. We present, to our knowledge, the first 360° circumferential volumes (two normal subjects, two subjects with pathology) of peripheral iris and iridocorneal angle structures obtained via an internal approach not typically available in the clinic.

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    13. Optical Coherence Tomography Accurately Measures Corneal Power Change from Laser Refractive Surgery

      Optical Coherence Tomography Accurately Measures Corneal Power Change from Laser Refractive Surgery

      Purpose To determine the ability of motion-corrected optical coherence tomography (OCT) to measure the corneal refractive power change due to LASIK. Design Evaluation of a diagnostic test or technology in a cohort. Subjects A total of 70 eyes from 37 subjects undergoing LASIK were measured preoperatively. A total of 39 eyes from 22 subjects were measured postoperatively and completed the study. Methods Consecutive patients undergoing LASIK at the Duke Eye Center who consented to participate were imaged with Placido-ring topography, Scheimpflug photography, and OCT on the day of their surgery. Patients were then reimaged with the same imaging systems at ...

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    14. Expanding OCT: Quanitifying the Cornea’s Optical Performance

      Expanding OCT: Quanitifying the Cornea’s Optical Performance

      Optical coherence tomography, a well-known method for imaging the retina, may allow physicians to perform quantitative metrology of the eye’s own optics. Swept-source OCT allows for simultaneous imaging of the cornea, iris and retina in living patients. Laser refractive surgeries such as laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) have brought better vision to tens of millions worldwide. But these techniques also exact a cost: because they work by reshaping the eye’s cornea, they make accurate measurement of the cornea’s optical parameters after surgery unreliable using conventional tools. That’s important, not only because inaccurate ...

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    15. Complete 360° circumferential SSOCT gonioscopy of the iridocorneal angle

      Complete 360° circumferential SSOCT gonioscopy of the iridocorneal angle

      The ocular iridocorneal angle is generally an optically inaccessible area when viewed directly through the cornea due to the high angle of incidence required and the large index of refraction difference between air and cornea (n air = 1.000 and n cornea = 1.376) resulting in total internal reflection. Gonioscopy allows for viewing of the angle by removing the aircornea interface through the use of a special contact lens on the eye. Gonioscopy is used clinically to visualize the angle directly but only en face. Optical coherence tomography (OCT) has been used to image the angle and deeper structures via ...

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    16. Fast Acquisition and Reconstruction of Optical Coherence Tomography Images via Sparse Representation

      Fast Acquisition and Reconstruction of Optical Coherence Tomography Images via Sparse Representation

      In this paper we present a novel technique, based on compressive sensing principles, for reconstruction and enhancement of multi-dimensional image data. Our method is a major improvement and generalization of the multi-scale sparsity based tomographic denoising (MSBTD) algorithm we recently introduced for reducing speckle noise. Our new technique exhibits several advantages over MSBTD, including its capability to simultaneously reduce noise and interpolate missing data. Unlike MSBTD, our new method does not require an a priori high-quality image from the target imaging subjectand thus offers the potential to shorten clinical imaging sessions. This novel image restoration method, which we termed ...

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    17. Correction of Ocular Shape in Retinal Optical Coherence Tomography and Effect on Current Clinical Measures

      Correction of Ocular Shape in Retinal Optical Coherence Tomography and Effect on Current Clinical Measures

      Purpose To address the misrepresentation of the eye in retinal optical coherence tomography (OCT) images and to examine the effect of this misrepresentation on retinal thickness measurements. Design Prospective case series. Methods Five subjects with recent orbital magnetic resonance imaging (MRI) scans and normal eye examinations were consented from the clinics of the Duke Eye Center. Each subject had both eyes imaged using a retinal spectral-domain OCT system and ocular biometry measured. Two types of individualized optical models of the subject eyes—numerical and analytical—were used to determine the spatial paths of the OCT A-scans. These paths were used ...

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    18. Quantitative single and multi-surface clinical corneal topography utilizing optical coherence tomography

      Quantitative single and multi-surface clinical corneal topography utilizing optical coherence tomography

      Successful surgical treatment of ocular astigmatism requires accurate characterization of both magnitude and axis of the astigmatism. Keratometry and topography are clinically widely used for this measurement; however, their analysis is limited to the anterior corneal surface. Unlike these techniques, optical coherence tomography (OCT) offers the advantage of measuring both the anterior and posterior corneal surface contributions. We present a technique to combine the local curvatures of both surfaces into a single pseudosurface suitable for clinical application. Building on prior work in distributed scanning OCT (DSOCT) to remove corrupting patient motion artifacts, we present the results of a pilot patient ...

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    19. Distributed scanning volumetric SDOCT for motion corrected corneal biometry

      Distributed scanning volumetric SDOCT for motion corrected corneal biometry

      We present a method, termed distributed scanning OCT (DSOCT), which reduces the effects of patient motion on corneal biometry utilizing current-generation clinically available spectral domain optical coherence tomography (SDOCT) systems. We first performed a pilot study of the power spectrum of normal patient axial eye motion based on repeated (M-mode) SDOCT. Using DSOCT to reduce the effects of patient motion, we conducted a preliminary patient study comparing the measured anterior and posterior corneal curvatures and the calculated corneal power to both corneal topography and Scheimpflug photography in normal subjects. The repeatability for the measured radius of curvature of both anterior ...

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    20. Corneal biometry from volumetric SDOCT and comparison with existing clinical modalities

      Corneal biometry from volumetric SDOCT and comparison with existing clinical modalities

      We present a comparison of corneal biometric values from dense volumetric spectral domain optical coherence tomography (SDOCT) scans to reference values in both phantoms and clinical subjects. We also present a new optically based “keratometric equivalent power” formula for SDOCT that eliminates previously described discrepancies between corneal power form SDOCT and existing clinical modalities. Phantom objects of varying radii of curvature and corneas of normal subjects were imaged with a clinical SDOCT system. The optically corrected three-dimensional surfaces were used to recover radii of curvature and power as appropriate. These were then compared to the manufacturer’s reference values in ...

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    21. Doppler velocity detection limitations in spectrometer-based versus swept-source optical coherence tomography

      Doppler velocity detection limitations in spectrometer-based versus swept-source optical coherence tomography

      Recent advances in Doppler techniques have enabled high sensitivity imaging of biological flow to measure blood velocities and vascular perfusion. Here we compare spectrometer-based and wavelength-swept Doppler OCT implementations theoretically and experimentally, characterizing the lower and upper observable velocity limits in each configuration. We specifically characterize the washout limit for Doppler OCT, the velocity at which signal degradation results in loss of flow information, which is valid for both quantitative and qualitative flow imaging techniques. We also clearly differentiate the washout effect from the separate phenomenon of phase wrapping. We demonstrate that the maximum detectable Doppler velocity is determined by ...

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    22. Robust automatic segmentation of corneal layer boundaries in SDOCT images using graph theory and dynamic programming

      Robust automatic segmentation of corneal layer boundaries in SDOCT images using graph theory and dynamic programming

      Segmentation of anatomical structures in corneal images is crucial for the diagnosis and study of anterior segment diseases. However, manual segmentation is a time-consuming and subjective process. This paper presents an automatic approach for segmenting corneal layer boundaries in Spectral Domain Optical Coherence Tomography images using graph theory and dynamic programming. Our approach is robust to the low-SNR and different artifact types that can appear in clinical corneal images. We show that our method segments three corneal layer boundaries in normal adult eyes more accurately compared to an expert grader than a second grader—even in the presence of significant ...

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    23. Doppler velocity detection limitations in spectrometer and swept-source Fourier-domain optical coherence tomography

      Doppler velocity detection limitations in spectrometer and swept-source Fourier-domain optical coherence tomography

      Recent advances in Doppler and variance techniques have enabled high sensitivity imaging in regions of biological flow to measure blood velocities and vascular perfusion. In recent years, the sensitivity and imaging speed benefits of Fourier domain OCT have become apparent. Spectrometer-based and wavelength-swept implementations have both undergone rapid development. Comparative analysis of the potential benefits and limitations for the various configurations would be useful for matching technology capabilities to specific clinical problems. Here we take a first step in such a comparative analysis by presenting theoretical predictions and experimental results characterizing the lower and upper observable velocity limits in spectrometer-based ...

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    24. Piezoelectric scanning mirrors for endoscopic optical coherence tomography

      A novel piezoelectric scanning mirror design for endoscopic optical coherence tomography (OCT) is presented. OCT is an interferometric technique providing microscopic tomographic sectioning of biological samples with mm-range penetration capability in tissue and is suited for integration with endoscopes using fiber-based light delivery to the sample. The piezoelectric scanning mirror was designed to provide wide-range rapid forwarding-looking scanning of the optical beam at the distal end of a compact catheter. The optical scanner provides a large ratio of mirror aperture to device size with rectangular mirror sizes ranging from 600 µm × 840 µm to 840 µm × 1600 µm. Static angular ...
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    1-24 of 24
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    Doppler velocity detection limitations in spectrometer and swept-source Fourier-domain optical coherence tomography Robust automatic segmentation of corneal layer boundaries in SDOCT images using graph theory and dynamic programming Doppler velocity detection limitations in spectrometer-based versus swept-source optical coherence tomography Corneal biometry from volumetric SDOCT and comparison with existing clinical modalities Distributed scanning volumetric SDOCT for motion corrected corneal biometry Correction of Ocular Shape in Retinal Optical Coherence Tomography and Effect on Current Clinical Measures Fast Acquisition and Reconstruction of Optical Coherence Tomography Images via Sparse Representation Expanding OCT: Quanitifying the Cornea’s Optical Performance Complete 360° circumferential gonioscopic optical coherence tomography imaging of the iridocorneal angle High performance OCTA enabled by combining features of shape, intensity, and complex decorrelation A Novel 3D Segmentation Approach for Extracting Retinal Layers from Optical Coherence Tomography Images Assessing the Outcomes of Focused Heating of the Skin by a Long-Pulsed 1064 nm Laser with an Integrated Scanner, Infrared Thermal Guidance, and Optical Coherence Tomography