1. Articles from Nicholas G. Strouthidis

    1-26 of 26
    1. Feature Of The Week 07/08/2018: Retinal Nerve Fibre Layer Thickness & Cognition - Results from UK Biobank

      Feature Of The Week 07/08/2018: Retinal Nerve Fibre Layer Thickness & Cognition - Results from UK Biobank

      Importance: Identifing potential screening tests for future cognitive decline is a priority for developing treatments for and the prevention of dementia. Objective: To examine the potential of retinal nerve fiber layer (RNFL) thickness measurement in identifying those at greater risk of cognitive decline in a large community cohort of healthy people. Design, Setting, and Participants: UK Biobank is a prospective, multicenter, community-based study of UK residents aged 40 to 69 years at enrollment who underwent baseline retinal optical coherence tomography imaging, a physical examination, and a questionnaire. The pilot study phase was conducted from March 2006 to June 2006, and ...

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    2. DRUNET: a dilated-residual U-Net deep learning network to segment optic nerve head tissues in optical coherence tomography images

      DRUNET: a dilated-residual U-Net deep learning network to segment optic nerve head tissues in optical coherence tomography images

      Given that the neural and connective tissues of the optic nerve head (ONH) exhibit complex morphological changes with the development and progression of glaucoma, their simultaneous isolation from optical coherence tomography (OCT) images may be of great interest for the clinical diagnosis and management of this pathology. A deep learning algorithm (custom U-NET) was designed and trained to segment 6 ONH tissue layers by capturing both the local (tissue texture) and contextual information (spatial arrangement of tissues). The overall Dice coefficient (mean of all tissues) was 0.91 ± 0.05 when assessed against manual segmentations performed by an expert observer ...

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    3. Association of Retinal Nerve Fiber Layer Thinning With Current and Future Cognitive Decline A Study Using Optical Coherence Tomography

      Association of Retinal Nerve Fiber Layer Thinning With Current and Future Cognitive Decline A Study Using Optical Coherence Tomography

      Importance Identifing potential screening tests for future cognitive decline is a priority for developing treatments for and the prevention of dementia. Objective To examine the potential of retinal nerve fiber layer (RNFL) thickness measurement in identifying those at greater risk of cognitive decline in a large community cohort of healthy people. Design, Setting, and Participants UK Biobank is a prospective, multicenter, community-based study of UK residents aged 40 to 69 years at enrollment who underwent baseline retinal optical coherence tomography imaging, a physical examination, and a questionnaire. The pilot study phase was conducted from March 2006 to June 2006, and ...

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    4. DRUNET: A Dilated-Residual U-Net Deep Learning Network to Digitally Stain Optic Nerve Head Tissues in Optical Coherence Tomography Images

      DRUNET: A Dilated-Residual U-Net Deep Learning Network to Digitally Stain Optic Nerve Head Tissues in Optical Coherence Tomography Images

      Given that the neural and connective tissues of the optic nerve head (ONH) exhibit complex morphological changes with the development and progression of glaucoma, their simultaneous isolation from optical coherence tomography (OCT) images may be of great interest for the clinical diagnosis and management of this pathology. A deep learning algorithm was designed and trained to digitally stain (i.e. highlight) 6 ONH tissue layers by capturing both the local (tissue texture) and contextual information (spatial arrangement of tissues). The overall dice coefficient (mean of all tissues) was 0.91 ± 0.05 when assessed against manual segmentations performed by an ...

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    5. A Deep Learning Approach to Digitally Stain Optical Coherence Tomography Images of the Optic Nerve Head

      A Deep Learning Approach to Digitally Stain Optical Coherence Tomography Images of the Optic Nerve Head

      Purpose. To develop a deep learning approach to digitally-stain optical coherence tomography (OCT) images of the optic nerve head (ONH). Methods. A horizontal B-scan was acquired through the center of the ONH using OCT (Spectralis) for 1 eye of each of 100 subjects (40 normal & 60 glaucoma). All images were enhanced using adaptive compensation. A custom deep learning network was then designed and trained with the compensated images to digitally stain (i.e. highlight) 6 tissue layers of the ONH. The accuracy of our algorithm was assessed (against manual segmentations) using the Dice coefficient, sensitivity, and specificity. We further studied ...

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    6. Feature Of The Week 05/28/2017: In Vivo 3-Dimensional Strain Mapping Confirms Large Optic Nerve Head Deformations Following Horizontal Eye Movements

      Feature Of The Week 05/28/2017: In Vivo 3-Dimensional Strain Mapping Confirms Large Optic Nerve Head Deformations Following Horizontal Eye Movements

      Glaucoma is characterized by an irreversible damage of retinal ganglion cells within the optic nerve head (ONH) at the back of the eye. Currently we know that elevated intraocular pressure (IOP) is associated with increased prevalence of glaucoma but not all glaucoma patients have an elevated IOP. The biomechanical theory of glaucoma hypothesizes that elevated (or fluctuating) IOP deforms the ONH tissues, including the lamina cribrosa (LC), and that these deformations drive retinal ganglion cell injury and death. However, IOP is not the only load that can deform the ONH. Eye movements have recently been hypothesized to be able to ...

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    7. A Digital Staining Algorithm for Optical Coherence Tomography Images of the Optic Nerve Head

      A Digital Staining Algorithm for Optical Coherence Tomography Images of the Optic Nerve Head

      Purpose : To digitally stain spectral-domain optical coherence tomography (OCT) images of the optic nerve head (ONH), and highlight either connective or neural tissues. Methods : OCT volumes of the ONH were acquired from one eye of 10 healthy subjects. We processed all volumes with adaptive compensation to remove shadows and enhance deep tissue visibility. For each ONH, we identified the four most dissimilar pixel-intensity histograms, each of which was assumed to represent a tissue group. These four histograms formed a vector basis on which we ‘projected' each OCT volume in order to generate four digitally stained volumes P1 to P4. Digital ...

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    8. In Vivo 3-Dimensional Strain Mapping Confirms Large Optic Nerve Head Deformations Following Horizontal Eye Movements

      In Vivo 3-Dimensional Strain Mapping Confirms Large Optic Nerve Head Deformations Following Horizontal Eye Movements

      Purpose : To measure lamina cribrosa (LC) strains (deformations) following abduction and adduction in healthy subjects and to compare them with those resulting from a relatively high acute intraocular pressure (IOP) elevation. Methods : A total of 16 eyes from 8 healthy subjects were included. Among the 16 eyes, 11 had peripapillary atrophy (PPA). For each subject, both optic nerve heads (ONHs) were imaged using optical coherence tomography (OCT) at baseline (twice), in different gaze positions (adduction and abduction of 20°) and following an acute IOP elevation of approximately 20 mm Hg from baseline (via ophthalmodynamometry). Strains of LC for all loading ...

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    9. Enhancement of Corneal Visibility in Optical Coherence Tomography Images with Corneal Opacification

      Enhancement of Corneal Visibility in Optical Coherence Tomography Images with Corneal Opacification

      Purpose : To establish and to rank the performance of a corneal adaptive compensation (CAC) algorithm in enhancing corneal images with scars acquired from three commercially available anterior segment optical coherence tomography (ASOCT) devices. Methods : Horizontal B-scans of the cornea were acquired from 10 patients using three ASOCT devices (Spectralis, RTVue, and Cirrus). We compared ASOCT image quality (with and without CAC) by computing the intralayer contrast (a measure of shadow removal), the interlayer contrast (a measure of tissue boundary visibility), and the tissue/background contrast (a measure of overall corneal visibility). All six groups (Spectralis, RTVue, Cirrus, Spectralis+CAC, RTVue ...

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    10. In Vivo 3-Dimensional Strain Mapping of the Optic Nerve Head Following Intraocular Pressure Lowering by Trabeculectomy

      In Vivo 3-Dimensional Strain Mapping of the Optic Nerve Head Following Intraocular Pressure Lowering by Trabeculectomy

      Purpose To map the 3-dimensional (3D) strain of the optic nerve head (ONH) in vivo after intraocular pressure (IOP) lowering by trabeculectomy (TE) and to establish associations between ONH strain and retinal sensitivity. Design Observational case series. Participants Nine patients with primary open-angle glaucoma (POAG) and 3 normal controls. Methods The ONHs of 9 subjects with POAG (pre-TE IOP: 25.3±13.9 mmHg; post-TE IOP: 11.8±8.6 mmHg) were imaged (1 eye per subject) using optical coherence tomography (OCT) (Heidelberg Spectralis, Heidelberg Engineering GmbH, Heidelberg, Germany) before (<21 days) and after (<50 days) TE. The imaging protocol ...

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    11. Spectral-Domain Optical Coherence Tomography Imaging in 67,321 Adults

      Spectral-Domain Optical Coherence Tomography Imaging in 67,321 Adults

      Purpose To derive macular thickness measures and their associations by performing rapid, automated segmentation of spectral-domain optical coherence tomography (SD OCT) images collected and stored as part of the UK Biobank (UKBB) study. Design Large, multisite cohort study in the United Kingdom. Analysis of cross-sectional data. Participants Adults from the United Kingdom aged 40 to 69 years. Methods Participants had nonmydriatic SD OCT (Topcon 3D OCT-1000 Mark II; Topcon GB, Newberry, Berkshire, UK) performed as part of the ocular assessment module. Rapid, remote, automated segmentation of the images was performed using custom optical coherence tomography (OCT) image analysis software (Topcon ...

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    12. Determinants of Optical Coherence Tomography–Derived Minimum Neuroretinal Rim Width in a Normal Chinese Population

      Determinants of Optical Coherence Tomography–Derived Minimum Neuroretinal Rim Width in a Normal Chinese Population

      Purpose. To characterize an optical coherence tomography (OCT)–derived parameter, Bruch's membrane opening–minimum rim width (BMO-MRW), and its association with demographic and clinical parameters in normal Chinese subjects. Methods. Right eyes of 466 consecutive healthy subjects from a population-based study of Singaporean Chinese underwent Cirrus OCT imaging. The retinal internal limiting membrane (ILM) and BMO were automatically delineated using the built-in Cirrus algorithm. The standard 36 interpolated radial B-scans (72 BMO points, 5° increments) of each optic nerve head were manually extracted from the central circle (3.46-mm diameter). We used Matlab to measure the shortest distance from ...

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    13. Lamina Cribrosa Visibility using Optical Coherence Tomography: Comparison of Devices and Effects of Image Enhancement Techniques

      Lamina Cribrosa Visibility using Optical Coherence Tomography: Comparison of Devices and Effects of Image Enhancement Techniques

      Purpose: To compare the visibility of the lamina cribrosa (LC) in optic disc images acquired from 60 glaucoma and 60 control subjects using three optical coherence tomography (OCT) devices, with and without enhanced depth imaging (EDI) and adaptive compensation (AC). Methods: A horizontal B-scan was acquired through the centre of the disc using two spectral-domain (Spectralis and Cirrus; with and without EDI) and a swept-source (DRI) OCT. AC was applied post-acquisition to improve image quality. To assess LC visibility, four masked observers graded the 1,200 images in a randomised sequence. The anterior LC was graded from 0 to 4 ...

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    14. Age-related Differences in Longitudinal Structural Change by Spectral Domain Optical Coherence Tomography in Early Experimental Glaucoma

      Age-related Differences in Longitudinal Structural Change by Spectral Domain Optical Coherence Tomography in Early Experimental Glaucoma

      Purpose. To characterize age-related differences in the magnitude of Spectral Domain Optical Coherence Tomography (SDOCT) structural change in early experimental glaucoma (EG). Methods. Both eyes from 4 young (1.4 - 2.6 yrs) and 4 old (18.6 - 21.9 yrs) rhesus monkeys were imaged at least 3 times at baseline, and then every 2 weeks following laser-induced, chronic, unilateral IOP elevation until the onset of EG (Confocal Scanning Laser Tomographic surface change confirmed twice). Two to 20 weeks after EG onset, animals were sacrificed and optic nerve axon counts for all eyes were performed. Masked operators delineated retinal and ...

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    15. Recent advances in OCT imaging of the lamina cribrosa

      Recent advances in OCT imaging of the lamina cribrosa

      The lamina cribrosa (LC) is believed to be the site of injury to retinal ganglion cell axons in glaucoma. The ability to visualise this structure has the potential to help increase our understanding of the disease and be useful in the early detection of glaucoma. While for many years the research on the LC was essentially dependent on histology and modelling, a number of recent advances in optical coherence tomography (OCT) have dramatically improved the ability to visualise the LC, such that it is now possible to image the LC in vivo in humans and animals. In this review, we ...

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    16. Longitudinal Detection of Optic Nerve Head Changes by Spectral Domain Optical Coherence Tomography in Early Experimental Glaucoma

      Longitudinal Detection of Optic Nerve Head Changes by Spectral Domain Optical Coherence Tomography in Early Experimental Glaucoma

      Purpose. To determine if the detection of spectral domain optical coherence tomography (SDOCT) optic nerve head (ONH) change precedes the detection of Confocal Scanning Laser Tomography (CSLT) ONH surface, SDOCT retinal nerve fiber layer (RNFL), Scanning Laser Perimetry (SLP) and multifocal electroretinography (mfERG) change in 8 experimental glaucoma (EG) eyes. Methods. Both eyes from 8 monkeys were tested at least 3 times at baseline, and then every 2 weeks following laser-induced chronic unilateral IOP elevation. Event and trend-based definitions of onset in both the control and EG eyes for a total of 11 SDOCT neural and connective tissue, CSLT surface ...

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    17. In vivo optic nerve head biomechanics: performance testing of a three-dimensional tracking algorithm

      In vivo optic nerve head biomechanics: performance testing of a three-dimensional tracking algorithm

      Measurement of optic nerve head (ONH) deformations could be useful in the clinical management of glaucoma. Here, we propose a novel three-dimensional tissue-tracking algorithm designed to be used in vivo . We carry out preliminary verification of the algorithm by testing its accuracy and its robustness. An algorithm based on digital volume correlation was developed to extract ONH tissue displacements from two optical coherence tomography (OCT) volumes of the ONH (undeformed and deformed). The algorithm was tested by applying artificial deformations to a baseline OCT scan while manipulating speckle noise, illumination and contrast enhancement. Tissue deformations determined by our algorithm were ...

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    18. Enhancement of Lamina Cribrosa Visibility in Optical Coherence Tomography Images using Adaptive Compensation

      Enhancement of Lamina Cribrosa Visibility in Optical Coherence Tomography Images using Adaptive Compensation

      Purpose. To improve the visibility of the lamina cribrosa (LC), including its posterior boundary, in optical coherence tomography (OCT) images of the human optic nerve head (ONH). Methods. An adaptive compensation algorithm was developed to overcome a limitation of our standard compensation algorithm, that is the over-amplification of noise at high depth. Such limitation currently hampers our ability to distinguish the posterior LC boundary. In adaptive compensation, standard compensation operations are performed until an energy threshold is reached, at which stage the compensation process is stopped to limit noise over-amplification in the deeper portion of the OCT image.The performance ...

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    19. Spectral-Domain Optical Coherence Tomography Enhanced Depth Imaging of the Normal and Glaucomatous Nonhuman Primate Optic Nerve Head

      Spectral-Domain Optical Coherence Tomography Enhanced Depth Imaging of the Normal and Glaucomatous Nonhuman Primate Optic Nerve Head
      Purpose. To test whether the enhanced depth imaging (EDI) modality improves anterior and posterior lamina cribrosa surface (ALCS and PLCS) visibility compared with conventional spectral-domain optical coherence tomography (SD-OCT). Methods. Conventional and EDI SD-OCT scans were obtained 30 minutes after IOP was manometrically lowered to 10 mm Hg in both eyes of 14 nonhuman primates (NHPs) with unilateral experimental glaucoma (EG). Thirteen horizontal and seven vertical radial B-scans of each SD-OCT data set were delineated by one operator masked to image type. Delineated ALCS and PLCS points were projected to 1 of 100 equal-sized subregions of the neural canal opening ...
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    20. Spectral Domain Optical Coherence Tomography (SDOCT) Enhanced Depth Imaging (EDI) of the Normal and Glaucomatous Non-human Primate (NHP) Optic Nerve Head (ONH)

      Spectral Domain Optical Coherence Tomography (SDOCT) Enhanced Depth Imaging (EDI) of the Normal and Glaucomatous Non-human Primate (NHP) Optic Nerve Head (ONH)
      Purpose: To test whether the EDI modality improves anterior and posterior lamina cribrosa surface (ALCS and PLCS) visibility compared to conventional SDOCT. Methods: Conventional and EDI SDOCT scans were obtained 30 minutes after IOP was manometrically lowered to 10 mmHg in both eyes of 14 non-human primates (NHPs) with unilateral experimental glaucoma (EG). Thirteen horizontal and 7 vertical radial B-scans of each SDOCT data set were delineated by one operator masked to image type. Delineated ALCS and PLCS points were projected to one of 100 equal-sized sub-regions of the neural canal opening (NCO) reference plane and the number of delineated ...
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    21. The Effect of Acute Intraocular Pressure Elevation on the Monkey Optic Nerve Head As Detected by Spectral Domain Optical Coherence Tomography

      The Effect of Acute Intraocular Pressure Elevation on the Monkey Optic Nerve Head As Detected by Spectral Domain Optical Coherence Tomography
      Purpose To determine whether acutely elevated IOP alters optic nerve head (ONH) structural parameters characterized in vivo using spectral domain optical coherence tomography (SDOCT). Methods Five rhesus macaques were tested under isoflurane anaesthesia. SDOCT images of the ONH of both eyes were acquired 30 minutes after IOP was stabilized to 10 mmHg and after 60 minutes to 45 mmHg. The internal limiting membrane, Bruch's Membrane/retinal pigment epithelium, neural canal opening (NCO) and anterior lamina cribrosa surface (ALCS) were delineated using custom software. Differences in SDOCT structural parameters between the two IOP levels were assessed using generalized estimating equations ...
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    22. Shadow removal and contrast enhancement in optical coherence tomography images of the human optic nerve head

      Shadow removal and contrast enhancement in optical coherence tomography images of the human optic nerve head

      Purpose.To improve the quality of optical coherence tomography (OCT) images of the optic nerve head (ONH). Methods.Two algorithms were developed, one to compensate for light attenuation and the other to enhance contrast in OCT images. The former was borrowed from developments in ultrasound imaging and proven suitable with either time- or spectral-domain OCT. The latter was based on direct application of pixel intensity exponentiation. The performances of these two algorithms were tested using spectral-domain OCT images of 4 adult ONHs. Results.Application of the compensation algorithm significantly reduced the intra-layer contrast (from 0.74 ± 0.16 to 0 ...

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    23. Longitudinal Change Detected by Spectral Domain Optical Coherence Tomography in the Optic Nerve Head and Peripapillary Retina in Experimental Glaucoma

      Longitudinal Change Detected by Spectral Domain Optical Coherence Tomography in the Optic Nerve Head and Peripapillary Retina in Experimental Glaucoma
      Purpose: To investigate whether longitudinal changes deep within the optic nerve head (ONH) are detectable by spectral domain optical coherence tomography (SDOCT) in experimental glaucoma (EG) and whether these changes are detectable at the onset of Heidelberg Retina Tomography (HRT) defined surface topography depression. Methods: Longitudinal SDOCT imaging (Heidelberg Spectralis) was performed in both eyes of 9 rhesus macaques every 1-3 weeks. One eye of each underwent trabecular laser-induced IOP elevation. Four masked operators delineated internal limiting membrane, retinal nerve fiber layer (RNFL), Bruch's Membrane/retinal pigment epithelium, neural canal opening (NCO) and anterior lamina cribrosa surface (ALCS) using ...
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    24. A Comparison of Optic Nerve Head Morphology Viewed by Spectral Domain Optical Coherence Tomography and By Serial Histology

      PURPOSE: To compare serial optic nerve head (ONH) histology with interpolated B-scans generated from a three-dimensional (3D) spectral domain OCT (SD-OCT) ONH volume acquired in vivo from the same normal monkey eye. METHODS: A 15°, ONH SD-OCT volume was acquired in a normal monkey eye, with IOP manometrically controlled at 10 mmHg, using the Heidelberg Spectralis. Following perfusion fixation at 10 mmHg, the ONH was trephined, embedded in a paraffin block and serial sagittal sections were cut at 4 µm intervals. The location of each histologic section was identified within the optic disc photograph by matching the position of the ...
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    25. Comparison of Clinical and Three-Dimensional Histomorphometric Optic Disc Margin Anatomy

      PURPOSE. To investigate the anatomic basis of the optic disc margin in the normal monkey eye by colocalizing optic disc photographs to three-dimensional (3D) histomorphometric reconstructions of the same optic nerve head. METHODS. Optic disc photographs from 28 normal monkey eyes were overlaid onto 3D central retinal vessel reconstructions generated as part of postmortem optic nerve histomorphometric reconstructions for each eye. Within each reconstruction, the Bruch’s membrane opening (BMO) was delineated. Alignment was achieved by matching the clinical vessel outline to the vessel reconstruction with parallel viewing software. An experienced observer viewed stereophotographs and marked the disc margin onto ...
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    26. The effect of acute intraocular pressure elevation on peripapillary retinal thickness, retinal nerve fiber layer thickness and retardance

      Purpose: To determine whether acutely elevated intraocular pressure (IOP) alters peripapillary retinal thickness, retinal nerve fiber layer thickness (RNFLT) or retardance. Methods: Nine adult non-human primates were studied under isoflurane anesthesia. Retinal and RNFL thicknesses were measured by spectral domain optical coherence tomography 30 min after IOP was set to 10 mmHg and 60 min after IOP was set to 45 mmHg. RNFL retardance was measured by scanning laser polarimetery in 10 min intervals for 30 min while IOP was 10 mmHg, then for 60 min while IOP was 45 mmHg, then for another 30 min after IOP was returned ...
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    1-26 of 26
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    Longitudinal Change Detected by Spectral Domain Optical Coherence Tomography in the Optic Nerve Head and Peripapillary Retina in Experimental Glaucoma Shadow removal and contrast enhancement in optical coherence tomography images of the human optic nerve head The Effect of Acute Intraocular Pressure Elevation on the Monkey Optic Nerve Head As Detected by Spectral Domain Optical Coherence Tomography Spectral Domain Optical Coherence Tomography (SDOCT) Enhanced Depth Imaging (EDI) of the Normal and Glaucomatous Non-human Primate (NHP) Optic Nerve Head (ONH) Spectral-Domain Optical Coherence Tomography Enhanced Depth Imaging of the Normal and Glaucomatous Nonhuman Primate Optic Nerve Head Feature Of The Week 05/28/2017: In Vivo 3-Dimensional Strain Mapping Confirms Large Optic Nerve Head Deformations Following Horizontal Eye Movements DRUNET: A Dilated-Residual U-Net Deep Learning Network to Digitally Stain Optic Nerve Head Tissues in Optical Coherence Tomography Images 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 Perimeter Medical Imaging Closes Oversubscribed $C4.4M Financing Time-domain optical coherence tomography system based on moving-optical-wedge interferometer