Optical coherence tomography (OCT) is a cross-sectional, micron-scale imaging modality with widespread clinical application. Typical OCT systems sacrifice lateral resolution to achieve long depths of focus for bulk tissue imaging, and hence tend to have better axial than lateral resolution. Such anisotropic resolution can obscure fine ultrastructural features. Furthermore, conventional OCT suffers from refraction-induced image distortions. Here, we introduce optical coherence refraction tomography (OCRT), which extends the superior axial resolution to the lateral dimension, synthesising undistorted cross-sectional image reconstructions from multiple conventional images acquired with angular diversity. In correcting refraction-induced distortions to register the OCT images, OCRT also achieves spatially resolved refractive index imaging. We demonstrate >3-fold improvement in lateral resolution as well as speckle reduction in imaging tissue ultrastructure, consistent with histology. With further optimisation in optical designs to incorporate angular diversity into clinical instruments, OCRT could be widely applied as an enhancement over conventional OCT.

Proliferative diabetic retinopathy (PDR) is a major cause of blindness in diabetic individuals. Optical coherence tomography (OCT) and OCT-angiography (OCTA) are noninvasive imaging techniques useful for the diagnosis and assessment of PDR. We aim to review several recent developments using OCT and discuss their present and potential future applications in the clinical setting. An electronic database search was performed so as to include all studies assessing OCT and/or OCTA findings in PDR patients published from 1 January 2020 to 31 May 2021. Thirty studies were included, and the most recently published data essentially focused on the higher detection rate of neovascularization obtained with widefield-OCT and/or OCTA (WF-OCT/OCTA) and on the increasing quality of retinal imaging with quality levels non-inferior to widefield-fluorescein angiography (WF-FA). There were also significant developments in the study of retinal nonperfusion areas (NPAs) using these techniques and research on the impact of PDR treatment on NPAs and on vascular density. It is becoming increasingly clear that it is critical to use adequate imaging protocols focused on optimized segmentation and maximized imaged retinal area, with ongoing technological development through artificial intelligence and deep learning. These latest findings emphasize the growing applicability and role of noninvasive imaging in managing PDR with the added benefit of avoiding the repetition of invasive conventional FA.

To identify and explain different artifacts in macular optical coherence tomography (OCT).

We performed a comprehensive search of the published literature in PubMed and Google Scholar to identify types, prevalence, etiology, clinical impact, and current methods for correction of various artifacts in optical coherence tomography angiography (OCTA) images. We found that the prevalence of OCTA image artifacts is fairly high. Artifacts associated with eye motion, misidentification of retinal layers, projections, and low optical coherence tomography signal are the most prevalent types. Artifacts in OCTA images are the major limitations of this diagnostic modality in clinical practice and identification of these artifacts and measures to mitigate them are essential for correct diagnosis and follow-up of patients.

Introduction: For many years, amblyopia was regarded as a disorder of the visual system in which an organic cause could not be identified. Optical Coherence Tomography opens new horizons in understanding the etiopathology of amblyopia and seems to highlight morphologic anomalies in the retina of the amblyopic eye. Purpose: The objective of this paper is to analyze the macular thickness, optic nerve changes, and choroidal thickness found in patients diagnosed with amblyopia based on trials reported in the literature. Material and methods: This study analyzes 30 clinical trials regarding amblyopia evaluation with Optical Coherence Tomography. The research articles analyzed were published between 2006 - 2016 and were identified on PubMed database. Results: 19 research studies focused on macular and nerve optic changes, 7 on choroidal changes and 6 on retinal changes after occlusion. The results were discussed according to the type of amblyopia, alteration of macular thickness, optic nerve changes, ganglion cell layer changes, and alteration of choroidal thickness. Conclusions: The results are of great variability, and it seems that macula and choroid involvement is more frequently suggested compared with optic nerve involvement. Abbreviations: OCT = Optical Coherence Tomography, RNFL = Retinal Nerve Fiber Layer, GCC = Ganglion Cell Complex, ACD = Anterior Chamber Depth, BCVA = Best Corrected Visual Acuity.

Enhanced S-cone syndrome is an autosomal recessive retinal dystrophy related to a defect in a nuclear receptor gene (NR2E3) that leads to alteration in cells development from rod to S-cone. This retinal dystrophy may be associated with retinal schisis. The aim of this report is to describe structural optical coherence tomography and optical coherence tomography angiography features in a case of enhanced S-cone syndrome associated with macular schisis.

Optical coherence tomography (OCT) is a widely used imaging technique in the micrometer regime, which gained accelerating interest in medical imaging in the last twenty years. In up-to-date OCT literature, certain simplifying assumptions are made for the reconstructions, but for many applications, a more realistic description of the OCT imaging process is of interest. In mathematical models, for example, the incident angle of light onto the sample is usually neglected or a plane wave description for the light-sample interaction in OCT is used, which ignores almost completely the occurring effects within an OCT measurement process. In this article, we make a first step to a quantitative model by considering the measured intensity as a combination of back-scattered Gaussian beams affected by the system. In contrast to the standard plane wave simplification, the presented model includes system relevant parameters, such as the position of the focus and the spot size of the incident laser beam, which allow a precise prediction of the OCT data. The accuracy of the proposed model-after calibration of all necessary system parameters-is illustrated by simulations and validated by a comparison with experimental data obtained from a 1300 nm swept-source OCT system.

Choroidal thickness is associated with many ocular conditions, interchangeability among different generations of optical coherence tomography is therefore important for both research purpose and clinical application. Hence, we compared choroidal thickness measurements between spectral-domain optical coherence tomography (SD-OCT) and swept-source optical coherence tomography (SS-OCT) in healthy paediatric eyes. A total of 114 children from the population-based Hong Kong Children Eye Study with mean age of 7.38 ± 0.82 years were included. Choroidal thickness of the right eye was measured by both devices. The central foveal choroidal thickness (CFCT) measured by SD-OCT and SS-OCT was 273.24 ± 54.29 μm and 251.84 ± 47.12 μm respectively. Inter-device correlation coefficient was 0.840 (95% CI 0.616-0.918). However, choroidal thickness obtained by SD-OCT was significantly thicker than that measured by SS-OCT with a mean difference of 21.40 ± 33.13 μm (P < 0.001). Bland-Altman limit of agreement on the relative difference scale for SD-OCT/SS-OCT was 86.33 μm. Validated conversion equation for translating SD-OCT CFCT measurement into SS-OCT was SS-OCT = 35.261 + 0.810 × SD-OCT. In conclusion, intra-class correlation coefficient (ICC) shows an acceptable agreement between SD-OCT and SS-OCT, however, there was a significant inter-device difference of choroidal thickness measurements in normal children eyes. Therefore, the measurements are not interchangeable.

Optical coherence tomography (OCT) is a modern imaging method with applicability in orthodontics. In recent years, there has been an increasing trend in the use of ceramic brackets. The aim of the present study was to investigate the effects of bonding metallic and ceramic brackets on tooth enamel, using optical coherence tomography. For this purpose, 20 permanent teeth we bonded and were subsequently debonded using a side cutter or anterior bracket removal pliers. Using the OCT technique, the enamel, the amount of adhesive remaining and the bracket fragments remaining on the tooth surface were analyzed following the debonding procedure. It was demonstrated that enamel cracks were present only in the samples bonded with ceramic brackets. At the same time, it was noted that the type of pliers did not affect the incidence and extent of damage to the enamel. The type of debonding technique (using the side cutter or the anterior removal pliers) used did not markedly affect the amount of adhesive remaining on the teeth. Thus, as demonstrated herein, by analyzing the enamel structure through the use of OCT, the quality of the processes and the materials used for manufacturing brackets can be increased.

To determine optic nerve and retinal damage in aquaporin-4 antibody (AQP4-IgG)-seropositive neuromyelitis optica spectrum disorders (NMOSD) in a large international cohort after previous studies have been limited by small and heterogeneous cohorts.

Optical coherence tomography is a new technology that provides an atraumatic "optical biopsy" providing both anatomical and possible histopathologic results. It has only recently been incorporated into the urological field. This paper highlights previous and prospective advances of optical coherence tomography in urology and its potential application in robotic urologic surgery.

This paper considers valuable visual assessment criteria for distinguishing between tumorous and non-tumorous tissues, intraoperatively, using cross-polarization OCT (CP OCT)-OCT with a functional extension, that enables detection of the polarization properties of the tissues in addition to their conventional light scattering. Materials and Methods: The study was performed on 176 ex vivo human specimens obtained from 30 glioma patients. To measure the degree to which the typical parameters of CP OCT images can be matched to the actual histology, 100 images of tumors and white matter were selected for visual analysis to be undertaken by three "single-blinded" investigators. An evaluation of the inter-rater reliability between the investigators was performed. Application of the identified visual CP OCT criteria for intraoperative use was performed during brain tumor resection in 17 patients. Results: The CP OCT image parameters that can typically be used for visual assessment were separated: (1) signal intensity; (2) homogeneity of intensity; (3) attenuation rate; (4) uniformity of attenuation. The degree of match between the CP OCT images and the histology of the specimens was significant for the parameters "signal intensity" in both polarizations, and "homogeneity of intensity" as well as the "uniformity of attenuation" in co-polarization. A test based on the identified criteria showed a diagnostic accuracy of 87-88%. Intraoperative in vivo CP OCT images of white matter and tumors have similar signals to ex vivo ones, whereas the cortex in vivo is characterized by indicative vertical striations arising from the "shadows" of the blood vessels; these are not seen in ex vivo images or in the case of tumor invasion. Conclusion: Visual assessment of CP OCT images enables tumorous and non-tumorous tissues to be distinguished. The most powerful aspect of CP OCT images that can be used as a criterion for differentiation between tumorous tissue and white matter is the signal intensity. In distinguishing white matter from tumors the diagnostic accuracy using the identified visual CP OCT criteria was 87-88%. As the CP OCT data is easily associated with intraoperative neurophysiological and neuronavigation findings this can provide valuable complementary information for the neurosurgeon tumor resection.

Absolute measurements of cerebral blood flow (CBF) are an important endpoint in studies of cerebral pathophysiology. Currently no accepted method exists for in vivo longitudinal monitoring of CBF with high resolution in rats and mice. Using three-dimensional Doppler Optical Coherence Tomography and cranial window preparations, we present methods and algorithms for regional CBF measurements in the rat cortex. Towards this end, we develop and validate a quantitative statistical model to describe the effect of static tissue on velocity sensitivity. This model is used to design scanning protocols and algorithms for sensitive 3D flow measurements and angiography of the cortex. We also introduce a method of absolute flow calculation that does not require explicit knowledge of vessel angles. We show that OCT estimates of absolute CBF values in rats agree with prior measures by autoradiography, suggesting that Doppler OCT can perform absolute flow measurements in animal models.

The mammalian cochlea has historically resisted attempts at high-resolution, non-invasive imaging due to its small size, complex three-dimensional structure, and embedded location within the temporal bone. As a result, little is known about the relationship between an individual's cochlear pathology and hearing function, and otologists must rely on physiological testing and imaging methods that offer limited resolution to obtain information about the inner ear prior to performing surgery. Micro-optical coherence tomography (μOCT) is a non-invasive, low-coherence interferometric imaging technique capable of resolving cellular-level anatomic structures. To determine whether μOCT is capable of resolving mammalian intracochlear anatomy, fixed guinea pig inner ears were imaged as whole temporal bones with cochlea in situ. Anatomical structures such as the tunnel of Corti, space of Nuel, modiolus, scalae, and cell groupings were visualized, in addition to individual cell types such as neuronal fibers, hair cells, and supporting cells. Visualization of these structures, via volumetrically-reconstructed image stacks and endoscopic perspective videos, represents an improvement over previous efforts using conventional OCT. These are the first μOCT images of mammalian cochlear anatomy, and they demonstrate μOCT's potential utility as an imaging tool in otology research.

High-resolution colposcopic optical coherence tomography (OCT) provides key anatomical measures, such as thickness and minor traumatic injury of vaginal epithelium, of the female reproductive tract noninvasively. This information can be helpful in both fundamental investigations in animal models and disease screenings in humans. We present a fiber-based visible-light OCT and two probe designs for colposcopic application. One probe conducts circular scanning using a DC motor, and the other probe is capable of three-dimensional imaging over a 4.6 × 4.6 - mm 2 area using a pair of galvo scanners. Using this colposcopic vis-OCT with both probes, we acquired high-resolution images from whole isolated macaque vaginal samples and identified biopsy lesions.

Lacrimal canaliculus (LC) has a key role in tear drainage, but it is difficult to evaluate the LC in detail, using the existing examinations. In this study, our novel LC imaging technique provided the high-resolution images of LC in a non-invasive manner. Three-dimensional images of LC were acquired via the palpebral conjunctiva from 20 healthy volunteers (20 eyes) and 10 patients with various lacrimal disorders (10 eyes), using optical coherence tomography (OCT) dacryography (OCTD). The LC images showed morphological differences between the vertical and horizontal segments. The function of LC could be evaluated by measuring the intralumen signal intensity over time after instillation of a contrast agent (2% rebamipide ophthalmic suspension). OCTD clearly visualised the blind extremity of the LC in four patients with punctal obstruction, which was useful for deciding the punctal incision location. In one patient with canalicular obstruction, contrast agent successfully highlighted the LC that had become narrow toward the site of obstruction. Significant differences were not found in the function and morphology of LC between the patients with NLDO and the healthy subjects. OCTD may be a useful tool for LC imaging, because it facilitates quantitative and simultaneous evaluation of LC morphology and function.

We introduce multi-directional optical coherence tomography (OCT), a technique for investigation of the scattering properties of directionally reflective tissue samples. By combining the concepts of multi-channel and directional OCT, this approach enables simultaneous acquisition of multiple reflectivity depth-scans probing a mutual sample location from differing angular orientations. The application of multi-directional OCT in retinal imaging allows for in-depth investigations on the directional reflectivity of the retinal nerve fiber layer, Henle's fiber layer and the photoreceptor layer. Major ophthalmic diseases (such as glaucoma or age-related macular degeneration) have been reported to alter the directional reflectivity properties of these retinal layers. Hence, the concept of multi-directional OCT might help to gain improved understanding of pathology development and progression. As a first step, we demonstrate the capabilities of multi-directional OCT in the eyes of healthy human volunteers.

Optical coherence tomography (OCT) has revolutionized the field of ophthalmology in the last three decades. As an OCT extension, OCT angiography (OCTA) utilizes a fast OCT system to detect motion contrast in ocular tissue and provides a three-dimensional representation of the ocular vasculature in a non-invasive, dye-free manner. The first OCT machine equipped with OCTA function was approved by U.S. Food and Drug Administration in 2016 and now it is widely applied in clinics. To date, numerous methods have been developed to aid OCTA interpretation and quantification. In this review, we focused on the workflow of OCTA-based interpretation, beginning from the generation of the OCTA images using signal decorrelation, which we divided into intensity-based, phase-based and phasor-based methods. We further discussed methods used to address image artifacts that are commonly observed in clinical settings, to the algorithms for image enhancement, binarization, and OCTA metrics extraction. We believe a better grasp of these technical aspects of OCTA will enhance the understanding of the technology and its potential application in disease diagnosis and management. Moreover, future studies will also explore the use of ocular OCTA as a window to link ocular vasculature to the function of other organs such as the kidney and brain.

Ocular manifestations have been described in the course of various types of vasculitis. However, there seems to be no routine ophthalmological examinations for patients suffering from those diseases. To ensure holistic care we aimed to investigate any retinal and choroidal abnormalities in patients suffering from primary vasculitis. The objective was to use non-invasive methods, which would not be time- and cost-consuming, yet would be helpful in routine tests. We conducted a prospective and observational study in 41 patients (78 eyes) with 5 types of primary vasculitis, including: Takayasu's arteritis; giant cell arteritis; Buerger's disease; granulomatosis with polyangiitis; and polyarteritis nodosa. A total of 44 healthy individuals were enrolled in the control group for comparison (88 eyes). With the use of optical coherence tomography, optical coherence tomography angiography, and MATLAB, the following parameters were assessed: choroidal thickness; vascularity index; area and perimeter of foveal avascular zone; and circularity index. The following parameters were lower in the study group compared to the control group: mean nasal and temporal CTs; mean central, temporal, and nasal CVI; and mean CI. In contrast, the results of mean central CT as well as the area and perimeter of FAZ were higher in the study group. The differences were statistically significant in the case of all parameters except for CI. Conducting routine ophthalmological examinations in patients diagnosed with vasculitis by assessment of the retina and choroid by measuring parameters like CT, CVI, area and perimeter of FAZ, and CI could be beneficial, as it may detect pathological changes before any ocular symptoms alarm the patients. CVI seems to be especially promising for choroidal evaluation, as it appears to be less influenced by various factors compared to CT.

We developed and demonstrated real-time compressive sensing (CS) spectral domain optical coherence tomography (SD-OCT) B-mode imaging at excess of 70 fps. The system was implemented using a conventional desktop computer architecture having three graphics processing units. This result shows speed gain of 459 and 112 times compared to the best CS implementations based on the MATLAB and C++, respectively, and that real-time CS SD-OCT imaging can finally be realized.