In vivo optical frequency domain imaging of human retina and choroid

Techniques for imaging the choroid and choroidal blood flow in vivo

The choroid, which is a highly vascularized layer between the retina and sclera, is essential for supplying oxygen and nutrients to the outer retina. Choroidal vascular dysfunction has been implicated in numerous ocular diseases, including age-related macular degeneration, central serous chorioretinopathy, polypoidal choroidal vasculopathy, and myopia. Traditionally, the in vivo assessment of choroidal blood flow relies on techniques such as laser Doppler flowmetry, laser speckle flowgraphy, pneumotonometry, laser interferometry, and ultrasonic color Doppler imaging. While the aforementioned methods have provided valuable insights into choroidal blood flow regulation, their clinical applications have been limited. Recent advancements in optical coherence tomography and optical coherence tomography angiography have expanded our understanding of the choroid, allowing detailed visualization of the larger choroidal vessels and choriocapillaris, respectively. This review provides an overview of the available techniques that can investigate the choroid and its blood flow in vivo. Future research should combine these techniques to comprehensively image the entire choroidal microcirculation and develop robust methods to quantify choroidal blood flow. The potential findings will provide a better picture of choroidal hemodynamics and its effect on ocular health and disease.

Two-stage adversarial learning based unsupervised domain adaptation for retinal OCT segmentation

BACKGROUND

Deep learning based optical coherence tomography (OCT) segmentation methods have achieved excellent results, allowing quantitative analysis of large-scale data. However, OCT images are often acquired by different devices or under different imaging protocols, which leads to serious domain shift problem. This in turn results in performance degradation of segmentation models.

PURPOSE

Aiming at the domain shift problem, we propose a two-stage adversarial learning based network (TSANet) that accomplishes unsupervised cross-domain OCT segmentation.

METHODS

In the first stage, a Fourier transform based approach is adopted to reduce image style differences from the image level. Then, adversarial learning networks, including a segmenter and a discriminator, are designed to achieve inter-domain consistency in the segmentation output. In the second stage, pseudo labels of selected unlabeled target domain training data are used to fine-tune the segmenter, which further improves its generalization capability. The proposed method was tested on cross-domain datasets for choroid or retinoschisis segmentation tasks. For choroid segmentation, the model was trained on 400 images and validated on 100 images from the source domain, and then trained on 1320 unlabeled images and tested on 330 images from target domain I, and also trained on 400 unlabeled images and tested on 200 images from target domain II. For retinoschisis segmentation, the model was trained on 1284 images and validated on 312 images from the source domain, and then trained on 1024 unlabeled images and tested on 200 images from the target domain.

RESULTS

The proposed method achieved significantly improved results over that without domain adaptation, with improvement of 8.34%, 55.82% and 3.53% in intersection over union (IoU) respectively for the three test sets. The performance is better than some state-of-the-art domain adaptation methods.

CONCLUSIONS

The proposed TSANet, with image level adaptation, feature level adaptation and pseudo-label based fine-tuning, achieved excellent cross-domain generalization. This alleviates the burden of obtaining additional manual labels when adapting the deep learning model to new OCT data.

High-resolution optical coherence tomography using a multi-level diffractive lens

We present a high-resolution optical coherence tomography (OCT) imaging system that utilizes a multi-level diffractive lens (MDL) to enhance lateral resolution. The system utilizes a polygon-based swept laser source with a center wavelength of 1,000 nm to achieve an axial resolution of 5.6 µm and an imaging depth of 1.4 mm using the bidirectional configuration of a semiconductor optical amplifier. The MDL significantly enhances the lateral resolution of the system, providing an extended depth of focus of 550 µm with an average lateral resolution of 8.5 µm. The effectiveness of this setup is validated through imaging of phantom and onion samples, demonstrating the system's capability for high-resolution deep tissue imaging. These findings underscore the potential of compact MDLs to significantly enhance the performance of OCT systems, offering a promising direction for advanced high-resolution imaging applications.

Multiple scattering suppression for in vivo optical coherence tomography measurement using the B-scan-wise multi-focus averaging method

We demonstrate a method that reduces the noise caused by multi-scattering (MS) photons in an in vivo optical coherence tomography image. This method combines a specially designed image acquisition (i.e., optical coherence tomography scan) scheme and subsequent complex signal processing. For the acquisition, multiple cross-sectional images (frames) are sequentially acquired while the depth position of the focus is altered for each frame by an electrically tunable lens. In the signal processing, the frames are numerically defocus-corrected, and complex averaged. Because of the inconsistency in the MS-photon trajectories among the different electrically tunable lens-induced defocus, this averaging reduces the MS signal. Unlike the previously demonstrated volume-wise multi-focus averaging method, our approach requires the sample to remain stable for only a brief period, approximately 70 ms, thus making it compatible with in vivo imaging. This method was validated using a scattering phantom and in vivo unanesthetized small fish samples, and was found to reduce MS noise even for unanesthetized in vivo measurement.

Retinal pigment epithelium melanin imaging using polarization-sensitive optical coherence tomography for patients with retinitis pigmentosa

This study aimed to evaluate the distribution of retinal pigment epithelium (RPE) melanin in patients with retinitis pigmentosa (RP) using entropy measurements by custom-made polarization-sensitive optical coherence tomography (PS-OCT) images, and compare entropy with the intensity of short-wavelength (SW) and near-infrared (NIR) autofluorescence (AF). We retrospectively reviewed the retinal images, including PS-OCT, SW-AF, and NIR-AF of patients with RP who had a hyperautofluorescent ring on AF. A total of 12 eyes of 12 patients (8 women and 4 men; mean age: 37.9 years) were included. There was a strong positive correlation between entropy value and NIR-AF intensity (r = 0.626, p < 0.001), and there was a very weak negative correlation between entropy value and SW-AF (r = − 0.197, p = 0.001). The mean values of the entropy in the foveal, temporal (2 mm from the fovea), and nasal (2 mm from the fovea) sections were 0.41 (± 0.09), 0.29 (± 0.08), and 0.26 (± 0.08), respectively. The entropy was significantly higher in the foveal section than in the temporal and nasal sections (p = 0.002 and p = 0.003, respectively). There was no significant difference between the entropies values for the temporal and nasal sections (p = 0.157). Age, logMAR best-corrected visual acuity, ellipsoid zone width, and central retinal thickness were not correlated with foveal entropy. We presented RPE melanin imaging in patients with RP using PS-OCT for the first time. PS-OCT can be a useful tool for monitoring patients with RP.

OCT applications in contact lens fitting

Optical Coherence Tomography (OCT) is a noninvasive, high-speed, high-resolution imaging technology based in the Michaelson interferometry. A near-infrared light beam is used to register the intensity variations for the light backscattered on each sample layer. Due to the high repeatability on corneal measurements, spectral domain OCT (SD-OCT) is the gold standard when talking about in vivo, non-invasive anterior segment imaging. Changes in the morphology of various ocular surfaces such as the cornea, conjunctiva, limbus or tear film with soft (SCL), rigid, corneal or scleral lens (SL) wear can be described by OCT measurements. For instance, evaluation of the corneoscleral region is essential on SL fitting. For orthokeratology lenses central epithelial thinning and peripheral thickening and their regression could be quantified with OCT after Ortho-K lens wear. Blood vessel compression on the landing zone as well as vault thickness and fluid reservoir (FR) turbidity could be imaged with OCT. Tear film evaluation on contact lens wearers is essential because its use could lead to variations on the biochemical components in tears. Changes in tear meniscus dynamics and several parameters such as volume (TMV), tear meniscus height (HMT) and turbidity could be determined with OCT and positively correlated with the instillation of different ophthalmic solutions with Non-Invasive Break Up Time (NIBUT) and Schirmer test values. This manuscript shows the increasing applicability of OCT technology for the in vivo characterization of contact lens fitting and interaction with the ocular surface in a faster, safer and non-invasive way. Future research will still allow exploring OCT imaging to its full potential in contact lens practice, as there is still a significant amount of information contained in the images that are not yet easy to extract, analyze and give clinical value.

Long cavity photonic crystal laser in FDML operation using an akinetic reflective filter

A novel configuration of a Fourier domain mode locked (FDML) laser based on silicon photonics platform is presented in this work that exploits the narrowband reflection spectrum of a photonic crystal (PhC) cavity resonator. Configured as a linear Fabry-Perot laser, forward biasing of a p-n junction on the PhC cavity allowed for thermal tuning of the spectrum. The modulation frequency applied to the reflector equalled the inverse roundtrip time of the long cavity resulting in stable FDML operation over the swept wavelength range. An interferometric phase measurement measured the sweeping instantaneous frequency of the laser. The silicon photonics platform has potential for very compact implementation, and the electro-optic modulation method opens the possibility of modulation speeds far beyond those of mechanical filters.

Swept-source optical coherence tomography imaging of the retinochoroid and beyond

Introduction: Swept-source optical coherence tomography (SS-OCT) imaging has ushered in an era of rapid and high-resolution imaging of the retinochoroid that provides detailed patho-anatomy of various layers.Areas covered: In this detailed review, the technology of swept-source imaging including its principles and working has been discussed. The applications of SS-OCT in various conditions including age-related macular degeneration, diabetic retinopathy, pachychoroid spectrum of diseases, and inflammatory vitreoretinal conditions have been elaborated. For each disease, a brief review of literature along with the utility of SS-OCT and optical coherence tomography angiography has been provided with supporting figures. The advantages of SS-OCT over spectral-domain have been discussed if there is sufficient evidence in the literature. Finally, the review summarizes the technological advantages in this field of retinal imaging.Expert opinion: The introduction of SS-OCT in our clinics has added newer devices in our armamentarium that can provide high-quality images of the deep retina and choroid. These advances in medical devices can help in improving our knowledge relating to the pathophysiology of diseases and their evolution. In the near future, rapid and high-resolution imaging may provide real-time volumetric information of the whole retina and the choroid that can be readily used for patient care.

Association between peripapillary scleral deformation and choroidal microvascular circulation in glaucoma

Peripapillary vessel density, which is reduced in eyes with glaucoma, has been proposed as a diagnostic tool for the desease and peripapillary choroidal microvasculature dropout(MvD) is considered one of pathophysiological manifestation of glaucomatous damage. However, little is known about the underlying pathogenic mechanism of dropout. According to recent studies, MvD is associated with structural changes in ONH structures. Therefore, we investigated the association between peripapillary scleral deformation and MvD. Data from 62 open-angle glaucoma (OAG) eyes with MvD and 36 eyes without MvD were analyzed in this study. And eyes with MvD were classified into two groups based on location: a juxtapapillary group and a non-juxtapapillary group for further analysis. More eyes with MvD had focal scleral deformation than did those without MvD (64.5% versus 2.8%; P < 0.001). Peripapillary choroidal thickness and focal scleral deformation were significantly associated with MvD. And juxtapapillary group was more associated with focal scleral deformation and coincidental RNFL defects than non-juxtapapillary groups. Peripapillary choroidal MvD was associated with the presence of scleral deformation, especially with juxtapapillary MvD, which was related to corresponding RNFL defects.

Lamina cribrosa surface position in idiopathic intracranial hypertension with swept-source optical coherence tomography

Purpose:

The purpose of this study is to compare the thickness and depth measurements of the lamina cribrosa (LC) obtained using a swept-source optical coherence tomography (SS-OCT) device in idiopathic intracranial hypertension (IIH) patients and healthy subjects.

Methods:

This retrospective, cross-sectional observational study included 16 eyes with IIH and 20 control eyes. The LC measurements with serial horizontal B scans of the optic nerve head were obtained using SS-OCT (Topcon 3D DRI OCT Triton). The anterior lamina surface (ALS) depth, posterior lamina surface (PLS) depth, and LC thickness measurements were evaluated.

Results:

In patients with IIH, the mean ALS depth was 225.00 ± 58.57 μm and the mean PLS depth was 449.75 ± 63.50 μm. In the IIH control group, the corresponding values were 359.40 ± 105.38 and 570.10 ± 99.41 μm (P < 0.05). The difference in LC thickness between the IIH and control subjects was not statistically significant.

Conclusion:

LC can be evaluated using an SS-OCT device. LC was displaced anteriorly in patients with IIH compared with normal controls. The assessment of LC level with SS-OCT in IIH cases is a valuable and reproducible adjunctive imaging method in terms of diagnosis and follow-up.

Phase-based OCT angiography in diagnostic imaging of pediatric retinoblastoma patients: abnormal blood vessels in post-treatment regression patterns

Phase-based OCT angiography of retinoblastoma regression patterns with a novel handheld 1050 nm clinical imaging system is demonstrated for the first time in children between 0 and 4 years old under general anesthesia. Angiography is mapped at OCT resolution by flow detection at every pixel with en-face projection from the volume between nerve fiber layer and retinal pigment epithelium. We show a striking difference between blood vasculature of healthy retina, and retinoblastoma regression patterns after chemotherapy, as well as varying complexity of abnormal vasculature in regression patterns types 2, 3, and 4. We demonstrate abnormal, tortuous and prominent vasculature in type 3 regression patterns having the highest risk of tumor recurrences and a lower probability to reduction into flat scars. The ability to visualize 3-D angiography might offer new insights in understanding of retinoblastoma development and its response to therapy.

Comparison of the Lamina Cribrosa Measurements Obtained by Spectral-Domain and Swept-Source Optical Coherence Tomography

Purpose/Aim of the study: The aim of this study was to compare the lamina cribrosa (LC) measurements obtained by Spectral-Domain Optical Coherence Tomography (SD-OCT) and Swept-Source Optical Coherence Tomography (SS-OCT) in the same eye and we also investigate how the differences in measurement will change in the presence of pseudoexfoliation glaucoma (PEG). Materials and Methods: A total of 30 patients from one institution have accepted. Detailed medical case histories and clinical examination, optic nerve head imaging using the SD-OCT (Heidelberg Engineering, Heidelberg, Germany) and SS-OCT (Triton; Topcon Medical Systems, Tokyo, Japan) for patients with pseudoexfoliation glaucoma and healthy volunteer. Results: Fifty-three eyes of the 30 patients (13 female, 17 male) were included in the study. Twenty-nine of eyes were healthy and 24 of eyes had pseudoexfoliation glaucoma. The mean age was 62 ± 7.3 years (range, 50-86 years). The difference between the mean Bruch's membrane opening distance measured by SD-OCT (1504.7 ± 154.2 µm) and by SS-OCT (1568.6 ± 193.3 µm) was statistically significant (p = .009). The difference between LC depth and LC thickness measurements between two OCT devices were not statistically significant. There was a negative correlation between the difference of two devices Bruch's membrane opening distance measurements and the cup/disc ratio (p = .007). Conclusion: Generally accepted belief is that lamina cribrosa visibility would be worse in healthy subjects who have thick prelaminar tissues, and better in individuals with glaucoma who had suffered the loss of prelaminar tissue. The difference between Bruch's membrane opening distance measurements taken with two devices was greater in normal eyes, and this difference was decreasing in glaucomatous eyes in our study. The Lamina Cribrosa measurement values shall not be directly compared between SD-OCT and SS-OCT.

Quality improvement of OCT angiograms with elliptical directional filtering

We present a method of OCT angiography (OCTA) data filtering for noise suppression and improved visualization of the retinal vascular networks in en face projection images. In our approach, we use a set of filters applied in three orthogonal axes in the three-dimensional (3-D) data sets. Minimization of artifacts generated in B-scan-wise data processing is accomplished by filtering the cross-sections along the slow scanning axis. A-scans are de-noised by axial filtering. The core of the method is the application of directional filtering to the C-scans, i.e. one-pixel thick sections of the 3-D data set, perpendicular to the direction of the scanning OCT beam. The method uses a concept of structuring, directional kernels of shapes matching the geometry of the image features. We use rotating ellipses to find the most likely local orientation of the vessels and use the best matching ellipses for median filtering of the C-scans. We demonstrate our approach in the imaging of a normal human eye with laboratory-grade spectral-domain OCT setup. The "field performance" is demonstrated in imaging of diabetic retinopathy cases with a commercial OCT device. The absolute complex differences method is used for the generation of OCTA images from the data collected in the most noise-wise unfavorable OCTA scanning regime-two frame scanning.

Optical coherence tomography in Optics Express [Invited]

Optical coherence tomography (OCT) is one of the most successful technologies in the history of biomedical optics. Optics Express played an important role in communicating groundbreaking technological achievements in the field of OCT, and, conversely, OCT papers are among the most frequently cited papers published in Optics Express. On the occasion of the 20th anniversary of the journal, this review analyzes the reasons for the success of OCT papers in Optics Express and discusses possible motivations for researchers to submit some of their best OCT papers to the journal.

Multiple Wavelength Optical Coherence Tomography Assessments for Enhanced Ex Vivo Intra-Cochlear Microstructural Visualization

The precise identification of intra-cochlear microstructures is an essential otorhinolaryngological requirement to diagnose the progression of cochlea related diseases. Thus, we demonstrated an experimental procedure to investigate the most optimal wavelength range, which can enhance the visualization of ex vivo intra-cochlear microstructures using multiple wavelengths (i.e., 860 nm, 1060 nm, and 1300 nm) based optical coherence tomography (OCT) systems. The high-resolution tomograms, volumetric, and quantitative evaluations obtained from Basilar membrane, organ of Corti, and scala vestibule regions revealed complementary comparisons between the aforementioned three distinct wavelengths based OCT systems. Compared to 860 nm and 1300 nm wavelengths, 1060 nm wavelength OCT was discovered to be an appropriate wavelength range verifying the simultaneously obtainable high-resolution and reasonable depth range visualization of intra-cochlear microstructures. Therefore, the implementation of 1060 nm OCT can minimize the necessity of two distinct OCT systems. Moreover, the results suggest that the performed qualitative and quantitative analysis procedure can be used as a powerful tool to explore further anatomical structures of the cochlea for future studies in otorhinolaryngology.

Compact akinetic swept source optical coherence tomography angiography at 1060 nm supporting a wide field of view and adaptive optics imaging modes of the posterior eye

Imaging of the human retina with high resolution is an essential step towards improved diagnosis and treatment control. In this paper, we introduce a compact, clinically user-friendly instrument based on swept source optical coherence tomography (SS-OCT). A key feature of the system is the realization of two different operation modes. The first operation mode is similar to conventional OCT imaging and provides large field of view (FoV) images (up to 45° × 30°) of the human retina and choroid with standard resolution. The second operation mode enables it to optically zoom into regions of interest with high transverse resolution using adaptive optics (AO). The FoV of this second operation mode (AO-OCT mode) is 3.0° × 2.8° and enables the visualization of individual retinal cells such as cone photoreceptors or choriocapillaris. The OCT engine is based on an akinetic swept source at 1060 nm and provides an A-scan rate of 200 kHz. Structural as well as angiographic information can be retrieved from the retina and choroid in both operational modes. The capabilities of the prototype are demonstrated in healthy and diseased eyes.

Optical Coherence Tomography Angiography

Optical coherence tomography angiography (OCTA) is a noninvasive approach that can visualize blood vessels down to the capillary level. With the advent of high-speed OCT and efficient algorithms, practical OCTA of ocular circulation is now available to ophthalmologists. Clinical investigations that used OCTA have increased exponentially in the past few years. This review will cover the history of OCTA and survey its most important clinical applications. The salient problems in the interpretation and analysis of OCTA are described, and recent advances are highlighted.

Review of adaptive optics OCT (AO-OCT): principles and applications for retinal imaging [Invited]

In vivo imaging of the human retina with a resolution that allows visualization of cellular structures has proven to be essential to broaden our knowledge about the physiology of this precious and very complex neural tissue that enables the first steps in vision. Many pathologic changes originate from functional and structural alterations on a cellular scale, long before any degradation in vision can be noted. Therefore, it is important to investigate these tissues with a sufficient level of detail in order to better understand associated disease development or the effects of therapeutic intervention. Optical retinal imaging modalities rely on the optical elements of the eye itself (mainly the cornea and lens) to produce retinal images and are therefore affected by the specific arrangement of these elements and possible imperfections in curvature. Thus, aberrations are introduced to the imaging light and image quality is degraded. To compensate for these aberrations, adaptive optics (AO), a technology initially developed in astronomy, has been utilized. However, the axial sectioning provided by retinal AO-based fundus cameras and scanning laser ophthalmoscope instruments is limited to tens of micrometers because of the rather small available numerical aperture of the eye. To overcome this limitation and thus achieve much higher axial sectioning in the order of 2-5µm, AO has been combined with optical coherence tomography (OCT) into AO-OCT. This enabled for the first time in vivo volumetric retinal imaging with high isotropic resolution. This article summarizes the technical aspects of AO-OCT and provides an overview on its various implementations and some of its clinical applications. In addition, latest developments in the field, such as computational AO-OCT and wavefront sensor less AO-OCT, are covered.

High-speed OCT light sources and systems [Invited]

Imaging speed is one of the most important parameters that define the performance of optical coherence tomography (OCT) systems. During the last two decades, OCT speed has increased by over three orders of magnitude. New developments in wavelength-swept lasers have repeatedly been crucial for this development. In this review, we discuss the historical evolution and current state of the art of high-speed OCT systems, with focus on wavelength swept light sources and swept source OCT systems.

VCSEL-based swept source for low-cost optical coherence tomography

We present a novel wavelength-swept laser source for optical coherence tomography (OCT) which is based on the conventional laser diode technology of the vertical-cavity surface-emitting laser (VCSEL). In our self-heating sweep VCSEL (SS-VCSEL), a VCSEL device is simply driven by ramped pulses of currents in direct intensity modulation. The intrinsic property of VCSEL produces a frequency-swept output through the self-heating effect. By the injected current, the temperature of the active region is gradually increased in this effect. Consequently, it changes the wavelength of the laser output by itself. In this study, various characteristics of our SS-VCSEL were experimentally investigated for low-cost instrumentation of a swept source OCT system. A low-cost SS-VCSEL-based OCT system was demonstrated in this research that provided an axial resolution of 135 μm in air, sensitivity of -91 dB and a maximum imaging range longer than 10 cm when our source was operated at a sweep repetition rate of 5 kHz with an output power of 0.41 mW. Based on the experimental observations, we believe that our SS-VCSEL swept source can be an economic alternative in some of low-cost or long-range applications of OCT.

Structural and functional human retinal imaging with a fiber-based visible light OCT ophthalmoscope

The design of a multi-functional fiber-based Optical Coherence Tomography (OCT) system for human retinal imaging with < 2 micron axial resolution in tissue is described. A detailed noise characterization of two supercontinuum light sources with different pulse repetition rates is presented. The higher repetition rate and lower noise source is found to enable a sensitivity of 96 dB with 0.15 mW light power at the cornea and a 98 microsecond exposure time. Using a broadband (560 ± 50 nm), 90/10, fused single-mode fiber coupler designed for visible wavelengths, the sample arm is integrated into an ophthalmoscope platform, similar to current clinical OCT systems. To demonstrate the instrument's range of operation, in vivo structural retinal imaging is also shown at 0.15 mW exposure with 10,000 and 70,000 axial scans per second (the latter comparable to commercial OCT systems), and at 0.03 mW exposure and 10,000 axial scans per second (below maximum permissible continuous exposure levels). Lastly, in vivo spectroscopic imaging of anatomy, saturation, and hemoglobin content in the human retina is also demonstrated.

Comparison of amplitude-decorrelation, speckle-variance and phase-variance OCT angiography methods for imaging the human retina and choroid

We compared the performance of three OCT angiography (OCTA) methods: speckle variance, amplitude decorrelation and phase variance for imaging of the human retina and choroid. Two averaging methods, split spectrum and volume averaging, were compared to assess the quality of the OCTA vascular images. All data were acquired using a swept-source OCT system at 1040 nm central wavelength, operating at 100,000 A-scans/s. We performed a quantitative comparison using a contrast-to-noise (CNR) metric to assess the capability of the three methods to visualize the choriocapillaris layer. For evaluation of the static tissue noise suppression in OCTA images we proposed to calculate CNR between the photoreceptor/RPE complex and the choriocapillaris layer. Finally, we demonstrated that implementation of intensity-based OCT imaging and OCT angiography methods allows for visualization of retinal and choroidal vascular layers known from anatomic studies in retinal preparations. OCT projection imaging of data flattened to selected retinal layers was implemented to visualize retinal and choroidal vasculature. User guided vessel tracing was applied to segment the retinal vasculature. The results were visualized in a form of a skeletonized 3D model.

Tissue thickness calculation in ocular optical coherence tomography

Thickness measurements derived from optical coherence tomography (OCT) images of the eye are a fundamental clinical and research metric, since they provide valuable information regarding the eye's anatomical and physiological characteristics, and can assist in the diagnosis and monitoring of numerous ocular conditions. Despite the importance of these measurements, limited attention has been given to the methods used to estimate thickness in OCT images of the eye. Most current studies employing OCT use an axial thickness metric, but there is evidence that axial thickness measures may be biased by tilt and curvature of the image. In this paper, standard axial thickness calculations are compared with a variety of alternative metrics for estimating tissue thickness. These methods were tested on a data set of wide-field chorio-retinal OCT scans (field of view (FOV) 60° x 25°) to examine their performance across a wide region of interest and to demonstrate the potential effect of curvature of the posterior segment of the eye on the thickness estimates. Similarly, the effect of image tilt was systematically examined with the same range of proposed metrics. The results demonstrate that image tilt and curvature of the posterior segment can affect axial tissue thickness calculations, while alternative metrics, which are not biased by these effects, should be considered. This study demonstrates the need to consider alternative methods to calculate tissue thickness in order to avoid measurement error due to image tilt and curvature.

Combined 60° Wide-Field Choroidal Thickness Maps and High-Definition En Face Vasculature Visualization Using Swept-Source Megahertz OCT at 1050 nm

PURPOSE

To demonstrate ultrahigh-speed swept-source optical coherence tomography (SS-OCT) at 1.68 million A-scans/s for choroidal imaging in normal and diseased eyes over a ∼60° field of view. To investigate and correlate wide-field three-dimensional (3D) choroidal thickness (ChT) and vascular patterns using ChT maps and coregistered high-definition en face images extracted from a single densely sampled Megahertz-OCT (MHz-OCT) dataset.

METHODS

High-definition, ∼60° wide-field 3D datasets consisting of 2088 × 1024 A-scans were acquired using a 1.68 MHz prototype SS-OCT system at 1050 nm based on a Fourier-domain mode-locked laser. Nine subjects (nine eyes) with various chorioretinal diseases or without ocular pathology are presented. Coregistered ChT maps, choroidal summation maps, and depth-resolved en face images referenced to either the retinal pigment epithelium or the choroidal-scleral interface were generated using manual segmentation.

RESULTS

Wide-field ChT maps showed a large inter- and intraindividual variance in peripheral and central ChT. In only four of the nine eyes, the location with the largest ChT was coincident with the fovea. The anatomy of the large lumen vessels of the outer choroid seems to play a major role in determining the global ChT pattern. Focal ChT changes with large thickness gradients were observed in some eyes.

CONCLUSIONS

Different ChT and vascular patterns could be visualized over ∼60° in patients for the first time using OCT. Due to focal ChT changes, a high density of thickness measurements may be favorable. High-definition depth-resolved en face images are complementary to cross sections and thickness maps and enhance the interpretation of different ChT patterns.

Human retinal imaging using visible-light optical coherence tomography guided by scanning laser ophthalmoscopy

We achieved human retinal imaging using visible-light optical coherence tomography (vis-OCT) guided by an integrated scanning laser ophthalmoscopy (SLO). We adapted a spectral domain OCT configuration and used a supercontinuum laser as the illumating source. The center wavelength was 564 nm and the bandwidth was 115 nm, which provided a 0.97 µm axial resolution measured in air. We characterized the sensitivity to be 86 dB with 226 µW incidence power on the pupil. We also integrated an SLO that shared the same optical path of the vis-OCT sample arm for alignment purposes. We demonstrated the retinal imaging from both systems centered at the fovea and optic nerve head with 20° × 20° and 10° × 10° field of view. We observed similar anatomical structures in vis-OCT and NIR-OCT. The contrast appeared different from vis-OCT to NIR-OCT, including slightly weaker signal from intra-retinal layers, and increased visibility and contrast of anatomical layers in the outer retina.

Morphologic characteristics of macular complications of a dome-shaped macula determined by swept-source optical coherence tomography

PURPOSE

To investigate the morphologic characteristics of macular complications of dome-shaped maculas using swept-source optical coherence tomography (OCT).

DESIGN

Retrospective observational case series.

METHODS

Axial length measurements and swept-source OCT were performed in 49 highly myopic eyes (in 5 male and 30 female subjects) with dome-shaped maculas. We classified the dome patterns and measured the central retinal thickness, central choroidal thickness, central scleral thickness, and the macular bulge height, and assessed the associations of these parameters with macular complications.

RESULTS

The central scleral thickness was significantly negatively correlated with age and the axial length. We classified the eyes into 3 groups: 6 with choroidal neovascularization (CNV group), 8 with retinal pigment epithelial detachment (PED group; 5 with serous retinal detachment), and 35 with no complications (no complications group). Nine eyes had a round dome and 40 had horizontally oriented oval-shaped domes. There were no significant differences in the frequency of macular complications between these patterns. The CNV group was significantly older and had a longer axial length than the other groups. The PED group had significantly larger values for both the central scleral thickness and bulge height than the other groups. The central choroidal thickness was significantly thinner in the CNV group than in the no complications group.

CONCLUSION

A dome-shaped macula results from relative thickening of the macular sclera, and this may lead to PED. Thinning of the sclera owing to long-term changes and elongation of the axis may develop CNV and cause visual impairment.

Relationship between retinal lesions and inward choroidal bulging in Vogt-Koyanagi-Harada disease

PURPOSE

To investigate the correlation between choroidal and retinal lesions in eyes with acute Vogt-Koyanagi-Harada disease (VKH) using optical coherence tomography (OCT) by using a new parameter, retinal pigment epithelium (RPE) undulation index, which quantitatively describes choroidal deformations.

DESIGN

Retrospective, observational, cross-sectional study.

METHODS

Spectral-domain OCT (SD OCT) and swept-source OCT images from a consecutive series of 42 eyes in 22 patients with acute VKH who underwent steroid therapy and 20 healthy eyes in 20 volunteers were analyzed retrospectively. Correlations between best-corrected visual acuity (BCVA), axial length change, and OCT parameters were examined. The RPE undulation index was defined as RPE line length to the total scan length ratio on a foveal-centered scan in the SD OCT image.

RESULTS

Eyes with acute VKH showed increased RPE undulation index, choroidal thickness, and retinal thickness compared to normal subjects, which were reduced following steroidal treatment (P < .0001, P = .0003, and P < .0001, respectively). RPE undulation index was related to choroidal thickness (r = 0.624, P = .0043), retinal thickness (r = 0.483, P = .0028), and BCVA (r = 0.588, P = .0002). Meanwhile, no statistically significant relationship was observed between choroidal thickness and retinal thickness. Axial length changes were significantly correlated with both choroidal thickness (r = 0.842, P < .0001) and RPE undulation index (r = 0.600, P = .0139).

CONCLUSIONS

This study demonstrated that the choroid was diffusely undulated and bulged inward in eyes with acute VKH. Correlations between RPE undulation index and choroid morphology, retinal thickness, and poor BCVA suggest that choroidal folding, quantified by RPE undulation index, is useful in assessing VKH disease severity.

All fiber optics circular-state swept source polarization-sensitive optical coherence tomography

A swept source (SS)-based circular-state (CS) polarization-sensitive optical coherence tomography (PS-OCT) constructed entirely with polarization-maintaining fiber optics components is proposed with the experimental verification. By means of the proposed calibration scheme, bulk quarter-wave plates can be replaced by fiber optics polarization controllers to, therefore, realize an all-fiber optics CS SSPS-OCT. We also present a numerical dispersion compensation method, which can not only enhance the axial resolution, but also improve the signal-to-noise ratio of the images. We demonstrate that this compact and portable CS SSPS-OCT system with an accuracy comparable to bulk optics systems requires less stringent lens alignment and can possibly serve as a technology to realize PS-OCT instrument for clinical applications (e.g., endoscopy). The largest deviations in the phase retardation (PR) and fast-axis (FA) angle due to sample probe in the linear scanning and a rotation angle smaller than 65 deg were of the same order as those in stationary probe setups. The influence of fiber bending on the measured PR and FA is also investigated. The largest deviations of the PR were 3.5 deg and the measured FA change by ~12 to 21 deg. Finally, in vivo imaging of the human fingertip and nail was successfully demonstrated with a linear scanning probe.

Improved visualization of deep ocular structures in glaucoma using high penetration optical coherence tomography

The introduction of optical coherence tomography (OCT) has revolutionized ophthalmology through the ability to non-invasively image the retina in vivo. Glaucoma is the leading cause of irreversible blindness worldwide. Despite major advances in imaging techniques, the pathogenesis of glaucoma remains poorly understood at present. The lamina cribrosa (LC) is the presumed site of axonal injury in glaucoma. Its thinning and deformation have been suggested to contribute to glaucoma development and progression by impeding axoplasmic flow within the optic nerve fibers, leading to apoptosis of retinal ganglion cells. To visualize the deep ocular structures such as the choroid and the LC, OCT imaging has been used, particularly the enhanced depth imaging (EDI)-OCT modality of spectral domain (SD)-OCT. However, the posterior laminar surface especially is not seen clearly using this method. A new generation of OCTs, swept-source (SS)-OCT, is able to image the LC and the choroid in vivo. SS-OCT employs a longer wavelength compared with the conventional OCT, generally set at 1050 nm (instead of 840 nm). We review current knowledge of the LC, findings from trials that use SD-OCT and EDI-OCT, and our experience with a prototype SS-OCT to quantify choroid changes and visualize the LC in its entirety.

Automated segmentation and characterization of choroidal vessels in high-penetration optical coherence tomography

An automated choroidal vessel segmentation and quantification method for high-penetration optical coherence tomography (OCT) was developed for advanced visualization and evaluation of the choroidal vasculature. This method uses scattering OCT volumes for the segmentation of choroidal vessels by using a multi-scale adaptive threshold. The segmented choroidal vessels are then processed by multi-scale morphological analysis to quantify the vessel diameters. The three-dimensional structure and the diameter distribution of the choroidal vasculature were then obtained. The usefulness of the method was then evaluated by analyzing the OCT volumes of normal subjects.

Choroidal thickness in central serous chorioretinopathy

PURPOSE

To study the choroidal thickness profile using high-penetration optical coherence tomography in central serous chorioretinopathy (CSC).

METHODS

Thirty-five eyes of 27 subjects with CSC and 35 healthy, age-matched control eyes were included. We observed the choroid using the prototype high-penetration optical coherence tomography. Fluorescein angiography and indocyanine green angiography were performed to identify the CSC location and activity. The choroidal thicknesses was measured manually in various conditions or locations, and the choroidal thickness maps were obtained from cube scans and calculating software and composed of nine sectors in the Early Diabetic Retinopathy Study chart.

RESULTS

The subfoveal choroidal thicknesses in all eyes with CSC were significantly (P < 0.01) greater than that in the control eyes. The choroidal thickness at the fovea and the fluorescein points of leakage were significantly (P < 0.01 for both comparisons) greater in eyes with CSC than the corresponding locations in the fellow eyes in patients with unilateral disease. Dilatation of the choroidal large vessels was significantly (P < 0.01) more common in CSC. The foveal choroidal thickness was significantly greater in eyes with venous dilatation (P < 0.01) than those without. The mean choroidal thickness was significantly (P < 0.05) greater in all sectors of the Early Diabetic Retinopathy Study chart except for the inner (P = 0.087) and outer (P = 0.053) inferior sectors. The percent mean choroidal thicknesses compared with the normal controls in the nasal sector were significantly (P < 0.05 and P < 0.01, respectively) greater in the inner and outer circles than in the superior, temporal, and inferior sectors.

CONCLUSION

The choroid is diffusely thickened in CSC likely because of the choroidal vascular dilatation. The nasal macula undergoes the greatest alterations in choroidal thickness compared with the other areas.

Peripapillary scleral deformation and retinal nerve fiber damage in high myopia assessed with swept-source optical coherence tomography

PURPOSE

To study peripapillary morphologic changes in highly myopic eyes using swept-source optical coherence tomography at a longer wavelength.

DESIGN

Prospective cross-sectional study.

METHODS

Peripapillary regions of 196 eyes of 107 patients with high myopia (refractive error, <-8.0 diopters or axial length, >26.0 mm) were analyzed quantitatively and qualitatively with an swept-source optical coherence tomography prototype system that uses a tunable laser light source operated at a 100,000-Hz A-scan repetition rate in the 1-μm wavelength region. The visual field was evaluated by standard automated perimetry. Area of peripapillary atrophy β and presence of scleral protrusion temporal to the optic disc were assessed.

RESULTS

Peripapillary atrophy β area, but not disc area, was significantly larger in eyes with visual field defect (3.16 ± 2.70 mm(2); range, 0.00 to 12.85 mm(2)) than those without visual field defect (2.31 ± 2.83 mm(2); range, 0.00 to 17.70 mm(2)). Temporal scleral protrusion was detected by color stereo disc photography in 22 (19.5%) of 113 eyes with visual field defect and in 4 (4.8%) of 83 eyes without visual field defect. Scleral bending demonstrated a wide range of angles (mean, 31.0 ± 21.1 degrees; range, 2 to 80 degrees). The angle of scleral bending, but not the distances from scleral bend to disc margin or foveal center, correlated significantly with retinal nerve fiber layer thickness above the bend (r = -0.557, P = .007) and visual field defect severity (r = -0.445, P = .038).

CONCLUSIONS

Swept-source optical coherence tomography visualizes peripapillary deep structures in high myopia. Some cases of high myopia may be affected by direct scleral compression or stretching at the peripapillary region.

High-resolution 1050 nm spectral domain retinal optical coherence tomography at 120 kHz A-scan rate with 6.1 mm imaging depth

We report a newly developed high speed 1050nm spectral domain optical coherence tomography (SD-OCT) system for imaging posterior segment of human eye. The system is capable of an axial resolution at ~10 µm in air, an imaging depth of 6.1 mm in air, a system sensitivity fall-off at ~6 dB/3mm and an imaging speed of 120,000 A-scans per second. We experimentally demonstrate the system's capability to perform phase-resolved imaging of dynamic blood flow within retina, indicating high phase stability of the SDOCT system. Finally, we show an example that uses this newly developed system to image posterior segment of human eye with a large view of view (10 × 9 mm(2)), providing detailed visualization of microstructural features from anterior retina to posterior choroid. The demonstrated system parameters and imaging performances are comparable to those that a typical 1 µm swept source OCT would deliver for retinal imaging.

Automatic segmentation of choroidal thickness in optical coherence tomography

The assessment of choroidal thickness from optical coherence tomography (OCT) images of the human choroid is an important clinical and research task, since it provides valuable information regarding the eye's normal anatomy and physiology, and changes associated with various eye diseases and the development of refractive error. Due to the time consuming and subjective nature of manual image analysis, there is a need for the development of reliable objective automated methods of image segmentation to derive choroidal thickness measures. However, the detection of the two boundaries which delineate the choroid is a complicated and challenging task, in particular the detection of the outer choroidal boundary, due to a number of issues including: (i) the vascular ocular tissue is non-uniform and rich in non-homogeneous features, and (ii) the boundary can have a low contrast. In this paper, an automatic segmentation technique based on graph-search theory is presented to segment the inner choroidal boundary (ICB) and the outer choroidal boundary (OCB) to obtain the choroid thickness profile from OCT images. Before the segmentation, the B-scan is pre-processed to enhance the two boundaries of interest and to minimize the artifacts produced by surrounding features. The algorithm to detect the ICB is based on a simple edge filter and a directional weighted map penalty, while the algorithm to detect the OCB is based on OCT image enhancement and a dual brightness probability gradient. The method was tested on a large data set of images from a pediatric (1083 B-scans) and an adult (90 B-scans) population, which were previously manually segmented by an experienced observer. The results demonstrate the proposed method provides robust detection of the boundaries of interest and is a useful tool to extract clinical data.

Shedding light on nanomedicine

Light is an electromagnetic radiation that can convert its energy into different forms (e.g., heat, chemical energy, and acoustic waves). This property has been exploited in phototherapy (e.g., photothermal therapy and photodynamic therapy (PDT)) and optical imaging (e.g., fluorescence imaging) for therapeutic and diagnostic purposes. Light-controlled therapies can provide minimally- or noninvasive spatiotemporal control as well as deep tissue penetration. Nanotechnology provides numerous advantages, including selective targeting of tissues, prolongation of therapeutic effect, protection of active payloads, and improved therapeutic indices. This review explores the advances that nanotechnology can bring to light-based therapies and diagnostics, and vice versa, including photo-triggered systems, nanoparticles containing photoactive molecules, and nanoparticles that are themselves photoactive. Limitations of light-based therapies such as photic injury and phototoxicity are discussed.

Imaging of the Lamina Cribrosa using Swept-Source Optical Coherence Tomography

The lamina cribrosa (LC) is the presumed site of axonal injury in glaucoma. Its deformation has been suggested to contribute to optic neuropathy by impeding axoplasmic flow within the optic nerve fibers, leading to apoptosis of retinal ganglion cells. To visualize the LC in vivo, optical coherence tomography (OCT) has been applied. Spectral domain (SD)-OCT, used in conjunction with recently introduced enhanced depth imaging (EDI)-OCT, has improved visualization of deeper ocular layers, but in many individuals it is still limited by inadequate resolution, poor image contrast and insufficient depth penetrance. The posterior laminar surface especially is not viewed clearly using these methods. New generation high-penetration (HP)-OCTs, also known as swept-source (SS)-OCT, are capable to evaluate the choroid in vivo to a remarkable level of detail. SS-OCTs use a longer wavelength (1,050 nm instead of 840 nm) compared to the conventional techniques. We review current knowledge of the LC, findings from trials that use SD-OCT and EDI-OCT, and our experience with a prototype SS-OCT to visualize the LC in its entirety.

Key Points

What is known?

•     The LC is the presumed site of axonal injury in glaucoma

•     Compared to spectral domain-OCT, enhanced depth imaging-OCT improves imaging of the LC

•     Even so, currently used SD-OCT techniques are restricted by poor wavelength penetrance of the deeper ocular layers

What our findings add?

•    SS-OCT may be a superior imaging modality for deep ocular structures

•    Prior studies used SS-OCT to evaluate choroidal thickness in both healthy and ‘normal tension glaucoma’ eyes

•    SS-OCT enables good evaluation of three-dimension (3D) lamina cribrosa morphology.

How to cite this article: Nuyen B, Mansouri K, Weinreb RN. Imaging of the Lamina Cribrosa using Swept-Source Optical Coherence Tomography. J Current Glau Prac 2012;6(3): 113-119.

Optical coherence tomography: future trends for imaging in glaucoma

Optical coherence tomography captures a major role in clinical assessment in eye care. Innovative hardware and software improvements in the technology would further enhance its usefulness. In this review, we present several promising initiatives currently in development or early phase of assessment that we expect to have a future impact on optical coherence tomography.

Automated measurement of choroidal thickness in the human eye by polarization sensitive optical coherence tomography

We present a new method to automatically segment the thickness of the choroid in the human eye by polarization sensitive optical coherence tomography (PS-OCT). A swept source PS-OCT instrument operating at a center wavelength of 1040 nm is used. The segmentation method is based entirely on intrinsic, tissue specific polarization contrast mechanisms. In a first step, the anterior boundary of the choroid, the retinal pigment epithelium, is segmented based on depolarization. In a second step, the choroid-sclera interface is found by using the birefringence of the sclera. The method is demonstrated in five healthy eyes. The mean repeatability (standard deviation) of thickness measurement was found to be 18.3 µm.

Logarithmic intensity and speckle-based motion contrast methods for human retinal vasculature visualization using swept source optical coherence tomography

We formulate a theory to show that the statistics of OCT signal amplitude and intensity are highly dependent on the sample reflectivity strength, motion, and noise power. Our theoretical and experimental results depict the lack of speckle amplitude and intensity contrasts to differentiate regions of motion from static areas. Two logarithmic intensity-based contrasts, logarithmic intensity variance (LOGIV) and differential logarithmic intensity variance (DLOGIV), are proposed for serving as surrogate markers for motion with enhanced sensitivity. Our findings demonstrate a good agreement between the theoretical and experimental results for logarithmic intensity-based contrasts. Logarithmic intensity-based motion and speckle-based contrast methods are validated and compared for in vivo human retinal vasculature visualization using high-speed swept-source optical coherence tomography (SS-OCT) at 1060 nm. The vasculature was identified as regions of motion by creating LOGIV and DLOGIV tomograms: multiple B-scans were collected of individual slices through the retina and the variance of logarithmic intensities and differences of logarithmic intensities were calculated. Both methods captured the small vessels and the meshwork of capillaries associated with the inner retina in en face images over 4 mm(2) in a normal subject.

Differential phase-contrast, swept-source optical coherence tomography at 1060 nm for in vivo human retinal and choroidal vasculature visualization

Human retinal and choroidal vasculature was visualized by a differential phase-contrast (DPC) method using high-speed, swept-source optical coherence tomography (SS-OCT) at 1060 nm. The vasculature was recognized as regions of motion by creating differential phase-variance (DPV) tomograms: multiple B-scans of individual slices through the retina were collected and the variance of the phase differences was calculated. DPV captured the small vessels and the meshwork of capillaries associated with the inner retina in en-face images over 4 mm(2). The swept-source laser at 1060 nm offered the needed phase sensitivity to perform DPV and generated en-face images that capture motion in the inner choroidal layer exceeding the capabilities of previous spectrometer-based instruments. In comparison with the power Doppler phase-shift method, DPV provided better visualization of the foveal avascular zone in en-face images.

Variable velocity range imaging of the choroid with dual-beam optical coherence angiography

In this study, we present dual-beam Doppler optical coherence angiography with variable beam separation. Altering beam distance, independently of the scanning protocol, provides a flexible way to select the velocity range of detectable blood flow. This system utilized a one-micrometer wavelength light source to visualize deep into the posterior eye, i.e., the choroid. Two-dimensional choroidal vasculature maps of a human subject acquired with different beam separations, and hence with several velocity ranges, are presented. Combining these maps yields a semi-quantitative visualization of axial velocity of the choroidal circulation. The proposed technique may be useful for identifying choroidal abnormalities that occur in pathological conditions of the eye.

Evaluation of the choroidal thickness using high-penetration optical coherence tomography with long wavelength in highly myopic normal-tension glaucoma

PURPOSE

To evaluate the choroidal thickness by high-penetration optical coherence tomography (OCT) using long wavelength in highly myopic normal-tension glaucoma (NTG).

DESIGN

Cross-sectional retrospective study.

METHODS

SETTINGS

Institutional.

PARTICIPANTS

Twelve eyes from 8 patients under 45 years old, diagnosed as NTG without any other ocular diseases, spherical equivalent refractive error between -6 and -12 diopters, and axial length greater than 26.5 mm; and 12 eyes of matched healthy volunteers.

INTERVENTION

Choroid was imaged with prototype high-penetration OCT and its thickness was measured.

MAIN OUTCOME MEASURES

Choroidal thickness at the fovea and 5 locations: 2 mm superior, temporal, and inferior to the center of the optic nerve head, and 2 mm superior (superotemporal) and 2 mm inferior (inferotemporal) to the temporal location.

RESULTS

Overall, the choroidal thickness in the NTG group was approximately 50% that in controls. Mean choroidal thickness in the NTG group was significantly thinner in the control group at the fovea (166 vs 276 μm, P < .001), superior (172 vs 241 μm, P < 0.05), superotemporal (161 vs 244 μm, P < .01), temporal (110 vs 161 μm, P < .01), and inferotemporal (115 vs 159 μm, P < .05) to the optic nerve head. Stepwise analysis disclosed that the foveal choroidal thickness is the most influential factor on the occurrence of NTG (P < .0001, R(2) = 0.4).

CONCLUSIONS

Choroidal thickness in highly myopic NTG is significantly thinner than in controls, at least in some specific locations. Choroidal thinning is somehow related with highly myopic NTG and may be a useful diagnostic parameter for myopic NTG.

Polarization sensitive optical coherence tomography in the human eye

Optical coherence tomography (OCT) has become a well established imaging tool in ophthalmology. The unprecedented depth resolution that is provided by this technique yields valuable information on different ocular tissues ranging from the anterior to the posterior eye segment. Polarization sensitive OCT (PS-OCT) extends the concept of OCT and utilizes the information that is carried by polarized light to obtain additional information on the tissue. Several structures in the eye (e.g. cornea, retinal nerve fiber layer, retinal pigment epithelium) alter the polarization state of the light and show therefore a tissue specific contrast in PS-OCT images. First this review outlines the basic concepts of polarization changing light-tissue interactions and gives a short introduction in PS-OCT instruments for ophthalmic imaging. In a second part a variety of different applications of this technique are presented in ocular imaging that are ranging from the anterior to the posterior eye segment. Finally the benefits of the method for imaging different diseases as, e.g., age related macula degeneration (AMD) or glaucoma is demonstrated.

Phase-stabilized optical frequency domain imaging at 1-µm for the measurement of blood flow in the human choroid

In optical frequency domain imaging (OFDI) the measurement of interference fringes is not exactly reproducible due to small instabilities in the swept-source laser, the interferometer and the data-acquisition hardware. The resulting variation in wavenumber sampling makes phase-resolved detection and the removal of fixed-pattern noise challenging in OFDI. In this paper this problem is solved by a new post-processing method in which interference fringes are resampled to the exact same wavenumber space using a simultaneously recorded calibration signal. This method is implemented in a high-speed (100 kHz) high-resolution (6.5 µm) OFDI system at 1-µm and is used for the removal of fixed-pattern noise artifacts and for phase-resolved blood flow measurements in the human choroid. The system performed close to the shot-noise limit (<1dB) with a sensitivity of 99.1 dB for a 1.7 mW sample arm power. Suppression of fixed-pattern noise artifacts is shown up to 39.0 dB which effectively removes all artifacts from the OFDI-images. The clinical potential of the system is shown by the detection of choroidal blood flow in a healthy volunteer and the detection of tissue reperfusion in a patient after a retinal pigment epithelium and choroid transplantation.