Doppler Optical Coherence Tomography Research Articles

Analysis of longitudinal sections of retinal vessels using Doppler OCT.

We present a new method for imaging retinal vessels that provides both structural and hemodynamic information. Our technique is based on a single beam OCT system with an integrated retinal tracker that enables recording of arbitrary scan patterns. We record longitudinal sections along the traces of retinal vessels. The tracker function enables the acquisition of multiple longitudinal sections along the same trace to provide high-quality averaged OCT scans as well as temporal changes of flow dynamics. The vessel walls are clearly identified as narrow, bright lines from which the vessel diameter can be retrieved as a function of position along the vessel. Furthermore, the Doppler angle can be obtained at each position along the vessel trace, enabling measurement of absolute blood flow by Doppler OCT analysis. The method is demonstrated in flow phantoms and in-vivo on retinal vessel bifurcations in healthy volunteers. In 7 of 9 imaged bifurcations, measured in- and outflow deviate by less than 11%, demonstrating the consistency of the method.

Phase unwrapping based on a residual en-decoder network for phase images in Fourier domain Doppler optical coherence tomography.

To solve the phase unwrapping problem for phase images in Fourier domain Doppler optical coherence tomography (DOCT), we propose a deep learning-based residual en-decoder network (REDN) method. In our approach, we reformulate the definition for obtaining the true phase as obtaining an integer multiple of 2π at each pixel by semantic segmentation. The proposed REDN architecture can provide recognition performance with pixel-level accuracy. To address the lack of phase images that are noise and wrapping free from DOCT systems for training, we used simulated images synthesized with DOCT phase image background noise features. An evaluation study on simulated images, DOCT phase images of phantom milk flowing in a plastic tube and a mouse artery, was performed. Meanwhile, a comparison study with recently proposed deep learning-based DeepLabV3+ and PhaseNet methods for signal phase unwrapping and traditional modified networking programming (MNP) method was also performed. Both visual inspection and quantitative metrical evaluation based on accuracy, specificity, sensitivity, root-mean-square-error, total-variation, and processing time demonstrate the robustness, effectiveness and superiority of our method. The proposed REDN method will benefit accurate and fast DOCT phase image-based diagnosis and evaluation when the detected phase is wrapped and will enrich the deep learning-based image processing platform for DOCT images.

Changes in Retinal Blood Flow in Response to an Experimental Increase in IOP in Healthy Participants as Assessed With Doppler Optical Coherence Tomography.

PurposeBlood flow autoregulation is an intrinsic mechanism of the healthy retinal vasculature to keep blood flow constant when ocular perfusion pressure (OPP) is changed. In the present study, we set out to investigate retinal blood flow in response to an experimental decrease in OPP in healthy participants using Doppler optical coherence tomography.MethodsFifteen healthy participants aged between 22 and 31 years (mean, 27 ± 3 years) were included in the present open study. IOP was increased stepwise via the suction cup method to induce a decrease in OPP. Retinal blood flow in arteries and veins was assessed using a custom-built Doppler optical coherence tomography system and pressure–flow relationships were calculated to assess autoregulation.ResultsSuction cup application induced a pronounced increase in IOP with a maximum value of 50.5 ± 8.0 mm Hg at the highest level of suction. Pressure–flow relationships revealed that blood flow was autoregulated until the OPP was decreased by approximately 21 mm Hg and started to decrease significantly when the OPP was reduced by 30 mm Hg. Retinal blood flow at the last suction period decreased at a maximum of –57.0 ± 22.3% and 65.2 ± 15.4% in retinal arteries and retinal veins, respectively. These changes in retinal blood flow were less pronounced than the decrease in OPP (–75.2 ± 19.2%), indicating retinal autoregulation.ConclusionsThe results of the present study confirm that retinal blood flow is autoregulated in response to changes in the OPP. Doppler optical coherence tomography has the potential to become a clinical tool for the investigation of retinal blood flow autoregulation in the future, because of its ability to assess the blood velocities and diameter of the retinal vessels parallel and therefore also their blood flow in absolute values. (Clinicaltrials.gov number NCT03398616)

Longitudinal Changes in Retinal Blood Flow in a Feline Retinal Vein Occlusion Model as Measured by Doppler Optical Coherence Tomography and Optical Coherence Tomography Angiography.

PurposeWe aimed to observe longitudinal changes in retinal blood flow (RBF) and structural transformations in capillaries using Doppler optical coherence tomography (DOCT) and optical coherence tomography angiography (OCTA) in a feline retinal blood occlusion (RVO) model.MethodsRVO was induced by argon green laser photocoagulation (PC) in six eyes of six cats. RBF was measured at a first-order retinal artery and vein by a DOCT flowmeter, and structural changes in the capillaries around the occluded vessels (12 × 12 and 3 × 3 mm) were assessed by OCTA before (at baseline); immediately after PC; and on days 1, 4, 7, and 14 thereafter. Systemic and ocular parameters were monitored during the observation period.ResultsThere were no significant differences in any systemic or ocular parameters before and after PC. Arterial RBF increased significantly on day 1 (160.6 ± 8.6% vs. baseline, P < 0.001) and decreased below baseline after day 1 through 14. Venous RBF decreased immediately after PC (17.4 ± 9.6% vs. baseline, P = 0.001) and then gradually increased afterwards, but did not return to baseline. OCTA showed dilatation of retinal venules immediately after PC to day 1. Collateral vessels began to form on day 4, had matured by day 7, and were pruned on day 14, which formed as mature as normal retinal venule diameters.ConclusionsWith increasing arterial RBF within 1 day after inducing RVO, venules gradually expanded to form collateral vessels, suggesting that collateral vessels originate from existing capillary networks, not neovascularization.

Blood flow rate estimation in optic disc capillaries and vessels using Doppler optical coherence tomography with 3D fast phase unwrapping.

The retinal volumetric flow rate contains useful information not only for ophthalmology but also for the diagnosis of common civilization diseases such as diabetes, Alzheimer's disease, or cerebrovascular diseases. Non-invasive optical methods for quantitative flow assessment, such as Doppler optical coherence tomography (OCT), have certain limitations. One is the phase wrapping that makes simultaneous calculations of the flow in all human retinal vessels impossible due to a very large span of flow velocities. We demonstrate that three-dimensional Doppler OCT combined with three-dimensional four Fourier transform fast phase unwrapping (3D 4FT FPU) allows for the calculation of the volumetric blood flow rate in real-time by the implementation of the algorithms in a graphics processing unit (GPU). The additive character of the flow at the furcations is proven using a microfluidic device with controlled flow rates as well as in the retinal veins bifurcations imaged in the optic disc area of five healthy volunteers. We show values of blood flow rates calculated for retinal capillaries and vessels with diameters in the range of 12-150 µm. The potential of quantitative measurement of retinal blood flow volume includes noninvasive detection of carotid artery stenosis or occlusion, measuring vascular reactivity and evaluation of vessel wall stiffness.

Spatiotemporal dynamics of pial collateral blood flow following permanent middle cerebral artery occlusion in a rat model of sensory-based protection: a Doppler optical coherence tomography study.

.There is a growing recognition regarding the importance of pial collateral flow in the protection from impending ischemic stroke both in preclinical and clinical studies. Collateral flow is also a major player in sensory stimulation-based protection from impending ischemic stroke. Doppler optical coherence tomography has been employed to image spatiotemporal patterns of collateral flow within the dorsal branches of the middle cerebral artery (MCA) as it provides a powerful tool for quantitative in vivo flow parameters imaging (velocity, flux, direction of flow, and radius of imaged branches). It was employed prior to and following dorsal permanent MCA occlusion (pMCAo) in rat models of treatment by protective sensory stimulation, untreated controls, or sham surgery controls. Unexpectedly, following pMCAo in the majority of subjects, some MCA branches continued to show anterograde blood flow patterns over time despite severing of the MCA. Further, in the presence of protective sensory stimulation, the anterograde velocity and flux were stronger and lasted longer than in retrograde flow branches, even within different branches of single subjects, but stimulated retrograde branches showed stronger flow parameters at 24 h. Our study suggests that the spatiotemporal patterns of collateral-based dorsal MCA flow are dynamic and provide a detailed description on the differential effects of protective sensory stimulation.

Advances in Doppler optical coherence tomography and angiography.

Since the first demonstration of Doppler optical coherence tomography (OCT) in 1997, several functional extensions of Doppler OCT have been developed, including velocimetry, angiogram, and optical coherence elastography. These functional techniques have been widely used in research and clinical applications, particularly in ophthalmology. Here, we review the principles, representative methods, and applications of different Doppler OCT techniques, followed by discussion on the innovations, limitations, and future directions of each of these techniques.

Phase unwrapping for Doppler spectral domain optical coherence tomography flow measurement.

Doppler optical coherence tomography (OCT) offers additional flow velocity information, which extends the application of OCT. Phase wrapping is the inherent problem that limits measureable range of Doppler OCT. We propose a phase unwrapping method which is suitable for correcting phase in Doppler OCT images. Points (pixels) in flow region are divided into groups according to the radial distance. Points in the same group are supposed to have close velocity. Phase unwrapping algorithm begins at the boundary layer group and is performed sequentially toward the center. Using the proposed criterion, points in a group are separated into two categories, signal points and noise points. Wrapping rounds are determined for signal points phase unwrapping. Mean value of the corrected signal points replaces the noise points for noise reduction. The method is validated with capillary tube flow phantom and in vivo blood flow.

Simultaneous Morphological and Flow Imaging Enabled by Megahertz Intravascular Doppler Optical Coherence Tomography.

We demonstrate three-dimensional intravascular flow imaging compatible with routine clinical image acquisition workflow by means of megahertz (MHz) intravascular Doppler Optical Coherence Tomography (OCT). The OCT system relies on a 1.1 mm diameter motorized imaging catheter and a 1.5 MHz Fourier Domain Mode Locked (FDML) laser. Using a post processing method to compensate the drift of the FDML laser output, we can resolve the Doppler phase shift between two adjoining OCT A-line datasets. By interpretation of the velocity field as measured around the zero phase shift, the flow direction at specific angles can be qualitatively estimated. Imaging experiments were carried out in phantoms, micro channels, and swine coronary artery in vitro at a speed of 600 frames/s. The MHz wavelength sweep rate of the OCT system allows us to directly investigate flow velocity of up to 37.5 cm/s while computationally expensive phase-unwrapping has to be applied to measure such high speed using conventional OCT system. The MHz sweep rate also enables a volumetric Doppler imaging even with a fast pullback at 40 mm/s. We present the first simultaneously recorded 3D morphological images and Doppler flow profiles. Flow pattern estimation and three-dimensional structural reconstruction of entire coronary artery are achieved using a single OCT pullback dataset.

Impact of atherosclerotic disease on cerebral microvasculature and tissue oxygenation in awake LDLR−/−hApoB+/+ transgenic mice

.We explore cortical microvasculature changes during the progression of atherosclerosis using young and old transgenic atherosclerotic (ATX) mice with thinned-skull cranial window. In awake animals, exploiting intrinsic signal optical imaging, Doppler optical coherence tomography, and two-photon microscopy, we investigate how the progression of atherosclerotic disease affects the morphology and function of cortical microvasculature as well as baseline cerebral tissue oxygenation. Results show that aged ATX mice exhibited weaker hemodynamic response in the somatosensory cortex to whisker stimulation and that the diameter of their descending arterioles and associated mean blood flow decreased significantly compared with the young ATX group. Data from two-photon phosphorescence lifetime microscopy indicate that old ATX mice had lower and more heterogeneous partial pressure of oxygen () in cortical tissue than young ATX mice. In addition, hypoxic micropockets in cortical tissue were found in old, but not young, ATX mice. Capillary red blood cell (RBC) flux, RBC velocity, RBC velocity heterogeneity, hematocrit, and diameter were also measured using line scans with two-photon fluorescence microscopy. When compared with the young group, RBC flux, velocity, and hematocrit decreased and RBC velocity heterogeneity increased in old ATX mice, presumably due to disturbed blood supply from arterioles that were affected by atherosclerosis. Finally, dilation of capillaries in old ATX mice was observed, which suggests that capillaries play an active role in compensating for an oxygen deficit in brain tissue.

Characterization of oviduct ciliary beat frequency using real time phase resolved Doppler spectrally encoded interferometric microscopy.

Ciliary activity, characterized by the coordinated beating of ciliary cells, generates the primary driving force for oviduct tubal transport, which is an essential physiological process for successful pregnancies. Malfunction of the cilium in the fallopian tube, or oviduct, may increase the risk of infertility and tubal pregnancy that can result in maternal death. While many ex-vivo studies have been carried out using bright field microscopy, this technique is not feasible for the in-vivo investigation of oviduct ciliary beating frequency (CBF). Optical coherence tomography (OCT) has been able to provide in-vivo CBF imaging in a mouse model, but its resolution may be insufficient to resolve the spatial and temporal features of the cilium. Our group has recently developed the phase resolved Doppler (PRD) OCT method to visualize ciliary strokes at ultra-high displacement sensitivity. However, the cross-sectional field of view (FOV) may not be ideal for visualizing the surface dynamics of ciliated tissue. In this study, we report on the development of phase resolved Doppler spectrally encoded interferometric microscopy (PRD-SEIM) to visualize the oviduct ciliary activity within an en face FOV. This novel real time imaging system offers micrometer spatial resolution, sub-nanometer displacement sensitivity, and the potential for in-vivo endoscopic adaptation. The feasibility of the approach has been validated through ex-vivo experiments where the porcine oviduct CBF has been measured across different temperature conditions and the application of a drug. CBF ranging from 8 to 12 Hz have been observed at different temperatures, while administration of lidocaine decreased the CBF and deactivated the motile cilia. This study will serve as a stepping stone to in-vivo oviduct ciliary endoscopy and future clinical translations.

Relating retinal blood flow and vessel morphology in sickle cell retinopathy

PurposeThe purpose of the current study was to determine associations between retinal blood flow and vessel morphology metrics in sickle cell retinopathy (SCR) and healthy normal control (NC) subjects.MethodsOptical coherence tomography angiography (OCTA) and Doppler OCT imaging were performed in 12 SCR (15 eyes) and 19 NC (26 eyes) subjects. Vessel tortuosity was measured using a dedicated image analysis algorithm applied to OCTA images. Vessel density and spacing between vessels were determined from OCTA images by a fractal dimension analysis method. Retinal blood flow was quantified using a phase-resolved technique applied to en face Doppler OCT images.ResultsThere was a significant association between increased retinal blood flow and increased vessel tortuosity (P = 0.03). Furthermore, increased retinal blood flow was associated with increased vessel density (P = 0.03) and decreased spacing between small vessels (P = 0.01). There was no significant association between retinal blood flow and spacing between large vessels (P = 0.11). Vessel tortuosity and blood flow were increased, whereas spacing between small vessels was decreased in SCR compared to NC group (P ≤ 0.03). There were no significant differences in vessel density or spacing between large vessels between the SCR and NC groups (P ≥ 0.31).ConclusionsAssociations between retinal hemodynamics and vessel morphology were reported, providing better understanding of retinal pathophysiology and insight into potential quantitative biomarkers to evaluate SCR.

Measurement of Vibrating Tympanic Membrane in an In Vivo Mouse Model Using Doppler Optical Coherence Tomography.

Optical coherence tomography (OCT) has a micro-resolution with a penetration depth of about 2 mm and field of view of about 10 mm. This makes OCT well suited for analyzing the anatomical and internal structural assessment of the middle ear. To study the vibratory motion of the tympanic membrane (TM) and its internal structure, we developed a phase-resolved Doppler OCT system using Kasai’s autocorrelation algorithm. Doppler optical coherence tomography is a powerful imaging tool which can offer the micro-vibratory measurement of the tympanic membrane and obtain the micrometer-resolved cross-sectional images of the sample in real-time. To observe the relative vibratory motion of individual sections (malleus, thick regions, and the thin regions of the tympanic membrane) of the tympanic membrane in respect to auditory signals, we designed an experimental study for measuring the difference in Doppler phase shift for frequencies varying from 1 to 8 kHz which were given as external stimuli to the middle ear of a small animal model. Malleus is the very first interconnecting region between the TM and cochlea. In our proposed study, we observed that the maximum change in Doppler phase shift was seen for the 4 kHz acoustic stimulus in the malleus, the thick regions, and in the thin regions of the tympanic membrane. In particular, the vibration signals were higher in the malleus in comparison to the tympanic membrane.

Imaging techniques in the diagnosis and monitoring of psoriasis.

Plaque psoriasis is a chronic, immune-mediated disease, which has a multifactorial etiopathogenesis. Practical non-invasive techniques to monitor plaque psoriasis progression and treatment are necessary. Imaging techniques available for psoriasis assessment may vary in terms of resolution, depth of penetration and visual representation. This review summarizes the current developments in the field of psoriasis non-invasive imaging techniques, such as dermoscopy, conventional ultrasound and high frequency ultrasonography (HFUS), videocapillaroscopy (VC), reflectance confocal microscopy (RCM), optical microangiography (OMAG), laser Doppler imaging (LDI), multiphoton tomography (MPT) and optical coherence tomography (OCT). The aim was to collect and analyze data concerning types, indications, advantages and disadvantages of modern imaging techniques for in vivo psoriasis assessment. We focused on two main methods, videodermoscopy and HFUS, which can be included in daily dermatologists' practice and which may assist in establishing diagnosis, as well as monitoring response to topical and/or systemic therapy of psoriasis. Dermoscopy may be useful for a first evaluation and may offer an understanding of the type and distribution of blood vessels, as well as the color of the scale and the background of the lesion. Videodermoscopy allows magnification and offers a detailed evaluation of the vessel type. The utility of HFUS consists mainly in monitoring therapy response. These methods may be comparable with virtual histopathology.

Dynamic Contrast Optical Coherence Tomography reveals laminar microvascular hemodynamics in the mouse neocortex in vivo

Studies of flow-metabolism coupling often presume that microvessel architecture is a surrogate for blood flow. To test this assumption, we introduce an in vivo Dynamic Contrast Optical Coherence Tomography (DyC-OCT) method to quantify layer-resolved microvascular blood flow and volume across the full depth of the mouse neocortex, where the angioarchitecture has been previously described. First, we cross-validate average DyC-OCT cortical flow against conventional Doppler OCT flow. Next, with laminar DyC-OCT, we discover that layer 4 consistently exhibits the highest microvascular blood flow, approximately two-fold higher than the outer cortical layers. While flow differences between layers are well-explained by microvascular volume and density, flow differences between subjects are better explained by transit time. Finally, from layer-resolved tracer enhancement, we also infer that microvascular hematocrit increases in deep cortical layers, consistent with predictions of plasma skimming. Altogether, our results show that while the cortical blood supply derives mainly from the pial surface, laminar hemodynamics ensure that the energetic needs of individual cortical layers are met. The laminar trends reported here provide data that links predictions based on the cortical angioarchitecture to cerebrovascular physiology in vivo.

Age-Related Decline of Retinal Oxygen Extraction in Healthy Subjects.

To investigate the age-dependence of total retinal blood flow and total retinal oxygen extraction in healthy subjects and determine their possible correlations with structural optical coherence tomography (OCT) parameters. This observational cross-sectional study consisted of 68 healthy subjects (mean ± SD age, 45.6 ± 16.3 years; 47% female). Total retinal oxygen extraction was calculated based on measurement of total retinal blood flow using bi-directional Doppler OCT and measurement of oxygen saturation using spectroscopic reflectometry. Retinal nerve fiber layer thickness was measured using OCT, and the total number of retinal ganglion cells was estimated based on a previous published model. Correlation of these parameters with age was studied and the association between structural OCT parameters and hemodynamic vascular parameters was calculated. Both structural and vascular parameters showed a significant decline with increasing age. The correlation coefficients were between r = -0.25 and r = -0.41. Furthermore, structural and vascular parameters were significantly correlated with each other. The strongest association was found between the level of total retinal oxygen extraction and the number of retinal ganglion cells (r = 0.75, P < 0.001). We showed that there was an age-related decline of retinal oxygen extraction. Levels of retinal oxygen extraction are correlated to retinal nerve fiber layer thickness and number of retinal ganglion cells. Our data partially explain the wide inter-individual variability in retinal blood flow values in healthy subjects. Longitudinal studies are required to study the time course of vascular and neuronal loss in humans.

Retinal Arteriole Pulse Waveform Analysis Using a Fully-Automated Doppler Optical Coherence Tomography Flowmeter: a Pilot Study.

PurposeTo evaluate the repeatability and reproducibility of the measurement of retinal arteriole pulse waveforms using a novel fully-automated Doppler optical coherence tomography (DOCT) flowmeter in healthy subjects.MethodsTwenty eyes of 20 healthy subjects were included to test the intrasession repeatability of pulse waveform analysis. DOCT measurements were performed based on a newly developed instantaneous Doppler angle measurement method. Upstroke time (UT), which is the time from the minimum to the maximum retinal blood velocity, and the resistance index (RI) of the retinal arteriole pulse waveform were measured. Coefficients of variation (CVs) and intraclass correlation coefficients (ICCs) were calculated. Interdevice reproducibility between two instruments was assessed in five eyes of five subjects.ResultsThe mean UT was 130.3 ms (range, 110.1–152.1 ms), and the mean RI was 0.66 (range, 0.51–0.82). The respective ICCs of UT and the RI for the intrasession repeatability of assessment were 0.87 and 0.78. The respective CVs of UT and the RI were 6.6 ± 3.3% and 4.7 ± 2.1%. Regarding interdevice reproducibility, there were no significant differences between the measurements derived from the instruments (P > 0.05).ConclusionsPulse waveform measurement in retinal arterioles using a fully-automated DOCT flowmeter exhibited good repeatability and interdevice reproducibility.Translational RelevanceThe above-described improved DOCT flowmeter system provides reasonably repeatable measurements of retinal arteriole pulse waveforms, potentially facilitating systemic-circulation abnormality monitoring. The examination of the circulation with the novel device can be potentially useful for evaluating systemic circulation.

Relating glaucomatous visual field loss to retinal oxygen delivery and metabolism.

To test the hypothesis that visual field (VF) loss is associated with decreased retinal blood flow, oxygen delivery and metabolism, and with increased retinal oxygen extraction fraction (OEF) in glaucomatous individuals. Glaucomatous subjects underwent automated perimetry, dual wavelength scanning laser ophthalmoscopy and Doppler optical coherence tomography imaging in order to measure mean deviation, central retinal arterial and venous diameter equivalents (CRAE and CRVE), oxygen saturation levels and total retinal blood flow (TRBF), respectively. Retinal oxygen delivery, metabolism and extraction fraction were derived from measurements of oxygen saturation and blood flow. Twenty eyes of 14 subjects were included in the study. Mean deviation was on average -13.76±8.70 dB. Mean CRAE and CRVE were 126±28 and 191±35μm, respectively. Mean TRBF and oxygen delivery were 34.3± 11.7μl/min and 6.5±2.6μl O2 /min, respectively. Mean oxygen metabolism and extraction fraction were 2.1±0.94μl O2 /min and 0.34±0.15, respectively. Visual field (VF) loss was associated with reduced CRAE and CRVE, TRBF and oxygen delivery and associated with increased OEF. Combined measurements of retinal blood flow and oxygen saturation in glaucomatous individuals suggest VF loss is associated with impaired oxygen delivery and augmented OEF.

Quantitative evaluation of primary retinitis pigmentosa patients using colour Doppler flow imaging and optical coherence tomography angiography.

To find the potential relation between changes in retinal large vessels and terminal vessels using colour Doppler flow imaging (CDFI) and optical coherence tomography angiography (OCTA) and to compare the respective advantages of CDFI and OCTA in evaluating vascular changes in retinitis pigmentosa (RP) patients. A prospective series of case study was conducted to enrol RP patients and age-matched controls, who were, respectively, imaged by CDFI and OCTA. Repeatability and reproducibility of both CDFI and OCTA were performed among healthy volunteers. The central retinal artery (CRA) was detected by CDFI analysis to provide parameters of peak systolic velocity (PSV), end-diastolic velocity (EDV) and time-averaged maximum velocity (TAMV). Retinal parameters were evaluated from OCTA images, including vascular area density (VAD) of the superficial vascular layer, the fovea avascular zone (FAZ) area and retinal thickness. RP patients were separated into a high-vision group and a low-vision group, according to median vision (0.3, LogMAR 0.5). Multiple comparisons were used to analyse the data between groups. A correlation analysis was used to determine the correlation between CDFI and OCTA parameters. Twenty RP patients (40 eyes) and thirteen normal volunteers (26 eyes) were enrolled in this study. Repeatability and reproducibility of the measurements by CDFI had higher CVs, from 4.5% to 15.4%, than those measurements by OCTA (<5%). All the CDFI and OCTA parameters examined had significant reductions in RP patients compared to those in the controls (p<0.01). Compared to the high-vision group, the low-vision group exhibited a statistically significant decrease in vascular parameters of the FAZ area, fovea VAD and parafovea nasal side VAD (p<0.05); as well as in the parameters of the fovea thickness, and the parafovea nasal, superior and inferior side thickness (p<0.05). From the correlation analysis, a significant association was found between the vision and CDFI parameters (PSV and time-averaged maximum velocity (TAMX), p<0.05), and the vision and OCTA parameters (FAZ area, fovea and nasal side VAD, retinal thickness in all sides, p<0.05). PSV and TAMX of the CRA were closely related to the OCTA superficial VAD in all sides, whereas the CDFI parameters showed poor correlation with retinal thickness. Colour Doppler flow imaging (CDFI) and OCTA parameters revealed a significant reduction in RP patients when compared to the controls. OCTA can detect vision-related microvascular and thickness changes around the macula between high- and low-vision groups, which happen earlier than the changes in large vessels. In addition to good repeatability and reproducibility, OCTA may have significant utility in the diagnosis and monitoring of disease progression in RP patients.

Investigating spontaneous retinal venous pulsation using Doppler optical coherence tomography

We demonstrate the advantages of optical coherence tomography (OCT) imaging for investigation of spontaneous retinal venous pulsation (SRVP). The pulsatile changes in venous vessel caliber are analyzed qualitatively and quantitatively using conventional intensity-based OCT as well as the functional extension Doppler OCT (DOCT). Single-channel and double-channel line scanning protocols of our multi-channel OCT prototype are employed to investigate venous pulsatile caliber oscillations as well as venous flow pulsatility in the eyes of healthy volunteers. A comparison to recordings of scanning laser ophthalmoscopy (SLO) – a standard en-face imaging modality for evaluation of SRVP – is provided, emphasizing the advantages of tomographic image acquisition. To the best of our knowledge, this is the first quantitative time-resolved investigation of SRVP and associated retinal perfusion characteristics using OCT.