Retinal vessel structure measurement using spectral-domain optical coherence tomography

Longitudinal Changes in the Retinal Nerve Fiber Layer Thickness in Amyotrophic Lateral Sclerosis and Parkinson's Disease

BACKGROUND AND PURPOSE

There is increasing evidence that the anterior visual pathways are involved in neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). This study investigated longitudinal changes in retinal nerve fiber layer (RNFL) thickness in patients with ALS and PD with the aim of better understanding their roles as biomarkers of disease progression.

METHODS

This study recruited 21 ALS patients, 19 age-matched PD patients, and 21 agematched healthy controls. Patient demographics and clinical scores relating to the respective diseases were documented. The RNFL thickness was measured using optical coherence tomography at baseline and after 6 months.

RESULTS

At baseline, the RNFL in the superior quadrant was significantly thinner in the patients with ALS than in healthy controls (109.90±22.41 µm vs. 127.81±17.05 µm [mean±standard deviation], p=0.008). The RNFL thickness did not differ significantly between the ALS and PD patients or between the PD patients and healthy controls. At 6 months, there was further significant RNFL thinning in patients with ALS, for both the overall thickness (baseline: median=94.5 µm, range=83.0-106.0 µm; follow-up: median=93.5 µm, range=82.5-104.5 µm, p=0.043) and the thickness in the inferior quadrant (median=126 µm, range=109.5-142.5 µm; and median=117.5 µm, range=98.5-136.5 µm; respectively, p=0.032). However, these changes were not correlated with the ALS functional scores. In contrast, the patients with PD did not demonstrate a significant change in RNFL thickness between the two time points.

CONCLUSIONS

The RNFL thickness is a promising biomarker of disease progression in patients with ALS but not in those with PD, which has a slower disease progression.

Lithospermum erythrorhizon Siebold & Zucc. extract reduces the severity of endotoxin-induced uveitis

BACKGROUND

Uveitis is an inflammatory eye condition that threatens vision, and effective anti-inflammatory treatments with minimal side effects are necessary to treat uveitis.

PURPOSE

This study aimed to investigate the effects of Lithospermum erythrorhizon Siebold & Zucc. against endotoxin-induced uveitis in rat and mouse models.

METHODS

Endotoxin-induced uveitis models of rats and mice were used to evaluate the effects of l. erythrorhizon treatment. Clinical inflammation scores and retinal thickness were assessed in the extract of l. erythrorhizon-treated rats. Histopathological examination revealed inflammatory cell infiltration into the ciliary body. Protein concentration, cellular infiltration, and prostaglandin-E2 levels were measured in the aqueous humor of the extract of l. erythrorhizon-treated rats. Protective effects of l. erythrorhizon on the anterior segment of the eye were examined in mice with endotoxin-induced uveitis. Additionally, we investigated the effect of l. erythrorhizon on the expression of pro-inflammatory cytokines [tumor necrosis factor alpha, interleukin-6, and interleukin-8] in lipopolysaccharide-stimulated THP1 human macrophages and examined the involvement of nuclear factor kappaB/activator protein 1 and interferon regulatory factor signaling pathways. Furthermore, three components of l. erythrorhizon were identified and assessed for their inhibitory effects on LPS-induced inflammation in RAW264.7 macrophage cells.

RESULTS

Treatment of the extract of l. erythrorhizon significantly reduced clinical inflammation scores and retinal thickening in rats with endotoxin-induced uveitis. Histopathological examination revealed decreased inflammatory cell infiltration into the ciliary body. The extract of l. erythrorhizon effectively reduced the protein concentration, cellular infiltration, and PG-E2 levels in the aqueous humor of rats with endotoxin-induced uveitis. In mice with endotoxin-induced uveitis, the extract of l. erythrorhizon demonstrated a protective effect on the anterior segment of the eye by reducing inflammation and retinal thickening. The extract of l. erythrorhizon suppressed the expression of pro-inflammatory cytokines (tumor necrosis factor alpha, interleukin-6, and interleukin-8) in lipopolysaccharide-induced inflammation in THP1 human macrophages, by modulating nuclear factor kappaB/activator protein 1 and interferon regulatory factor signaling pathways. Moreover, shikonin, acetylshikonin, and β, β-dimethylacryloylshikonin showed dose-dependent inhibition of nitric oxide, tumor necrosis factor alpha and interleukin-6 production in RAW264.7 macrophage cells.

CONCLUSION

The extract of l. erythrorhizon is a potential therapeutic agent for uveitis management. Administration of the extract of l. erythrorhizon led to reduced inflammation, retinal thickening, and inflammatory cell infiltration in rat and mouse models of uveitis. The compounds (shikonin, acetylshikonin, and β, β-dimethylacryloylshikonin) identified in this study played crucial roles in mediating the anti-inflammatory effects of l. erythrorhizon. These findings indicate that the extract of l. erythrorhizon and its constituent compounds are promising candidates for further research and development of novel treatment modalities for uveitis.

Adaptive vessel tracing and segmentation in OCT enables the robust detection of wall-to-lumen ratio abnormalities in 5xFAD mice

The wall-to-lumen ratio (WLR) of retinal blood vessels promises a sensitive marker for the physiological assessment of eye conditions. However, in vivo measurement of vessel wall thickness and lumen diameter is still technically challenging, hindering the wide application of WLR in research and clinical settings. In this study, we demonstrate the feasibility of using optical coherence tomography (OCT) as one practical method for in vivo quantification of WLR in the retina. Based on three-dimensional vessel tracing, lateral en face and axial B-scan profiles of individual vessels were constructed. By employing adaptive depth segmentation that adjusts to the individual positions of each blood vessel for en face OCT projection, the vessel wall thickness and lumen diameter could be reliably quantified. A comparative study of control and 5xFAD mice confirmed WLR as a sensitive marker of the eye condition.

Narrowing Ratio of Retinal Veins at Arteriovenous Crossing in Patients With Branch Retinal Vein Occlusion Versus That in Healthy Individuals

Purpose

This cross-sectional study aimed to clarify the differences in the retinal venous narrowing ratio (VNR) at retinal arteriovenous crossing by optical coherence tomography (OCT) among the eyes with branch retinal vein occlusion (BRVO), fellow eyes of patients with BRVO, and eyes of individuals without BRVO and to determine factors that influence the VNR.

Methods

We studied 31 eyes of young participants, 54 eyes of an older control group, 56 fellow eyes of patients with BRVO, and 48 eyes with BRVO. Cross-sectional OCT images were used to determine the VNR at two arteriovenous crossings per eye.

Results

Overall, 378 arteriovenous crossings were analyzed. The VNR of arterial overcrossings of fellow eyes (27.7% ± 11.1%) and BRVO eyes (27.3% ± 9.76%) were significantly higher than those in the young (16.0% ± 7.9%, all P < 0.001) and control (22.0% ± 8.81%, P < 0.001, P = 0.003, respectively) groups. The VNR of arterial overcrossings was significantly larger than that of venous overcrossings (24.0% ± 10.5% vs. 20.6% ± 13.0%, P = 0.021). A linear mixed-effects model showed that the VNR was significantly higher in arterial overcrossings, crossings with larger arterial internal diameters, smaller venous internal diameters, and participants with older age and a BRVO history.

Conclusions

The VNR in arterial overcrossings was higher in BRVO eyes and even in the fellow eyes. Thus, a higher VNR in arterial overcrossings may contribute to BRVO development, and crossings with factors contributing to higher VNR might be associated with a risk of BRVO.

Non-Invasive Retinal Blood Vessel Wall Measurements with Polarization-Sensitive Optical Coherence Tomography for Diabetes Assessment: A Quantitative Study

Diabetes affects the structure of the blood vessel walls. Since the blood vessel walls are made of birefringent organized tissue, any change or damage to this organization can be evaluated using polarization-sensitive optical coherence tomography (PS-OCT). In this paper, we used PS-OCT along with the blood vessel wall birefringence index (BBI = thickness/birefringence2) to non-invasively assess the structural integrity of the human retinal blood vessel walls in patients with diabetes and compared the results to those of healthy subjects. PS-OCT measurements revealed that blood vessel walls of diabetic patients exhibit a much higher birefringence while having the same wall thickness and therefore lower BBI values. Applying BBI to diagnose diabetes demonstrated high accuracy (93%), sensitivity (93%) and specificity (93%). PS-OCT measurements can quantify small changes in the polarization properties of retinal vessel walls associated with diabetes, which provides researchers with a new imaging tool to determine the effects of exercise, medication, and alternative diets on the development of diabetes.

Retinal arteriolar parameters as a surrogate marker of intracranial vascular pathology

Introduction

Development of novel diagnostic tools is a top research priority in vascular dementia. A major obstacle is the lack of a simple, non-invasive method to visualize cerebral arteriolar walls in vivo. Retinal arterioles offer a window into the cerebral circulation.

Methods

Intensity-based retinal arteriolar visualization in optical coherence tomography (I-bRAVO) was applied to evaluate mean wall thickness (MWT) and wall-to-lumen ratio (WLR) in 250 subjects with sporadic and genetic cerebral small vessel disease (CSVD), non-vascular neurodegenerative diseases (NVND), and healthy controls (HC) in association with imaging and cognitive markers.

Results

MWT and WLR were higher in CSVD, associated with severity of vascular white matter lesions, and correlated with magnetic resonance imaging-based intracranial arteriolosclerosis score. WLR correlated with gray and white matter volume and differentiated asymptomatic sporadic CSVD from HC (area under the curve = 0.82).

Discussion

I-bRAVO is a rapid, non-invasive tool. MWT and WLR were associated with imaging markers of CSVD and could contribute to early identification of sporadic CSVD.

Force of lifelong crystalline lens growth: chronic traumatic mechanical insult to the choroid

PURPOSE

To calculate the forces applied to the uvea and retina as a result of lifelong crystalline lens growth.

DESIGN

Retrospective study.

SETTING

MRI Research, Inc., Middleburg Heights, Ohio; Institute of Ophthalmology and Visual Science UMDNJ-New Jersey Medical School, Newark, New Jersey; USC Psychology University of Southern California, Los Angeles.

METHODS

Magnetic resonance images were acquired from 15 phakic/pseudophakic eye pairs in patients with cataract (ages 46 to 83 years). Choroidal lengths were measured. The forces required to produce differences between phakic/pseudophakic choroidal lengths were calculated.

RESULTS

The length of the choroid is greater in the phakic eye compared with the corresponding pseudophakic eye (n = 15), and this difference increases with age (P = .00006; power = 0.99). The corresponding choroidal strain also increases with age (P = .00003, power = 0.99) as do the forces required to produce such a change in choroidal length (P = .000008, power = 0.99).

CONCLUSIONS

The authors theorize that lifelong crystalline lens growth applies a chronic, traumatic, mechanical insult to the uvea and retina. This previously unknown, ever-increasing, force appears to stretch the choroidal tissue and may be an intraocular pressure-independent modifiable risk factor for retinal disease. Implications exist for understanding the pathophysiology of retinal diseases in the aging eye that are often comorbid with cataracts, for example, glaucoma, macular degeneration, and diabetic retinopathy.

Axial Stretching of Vessels in the Retinal Vascular Plexus With 3D OCT-Angiography

Purpose

The purpose of this study is to describe and quantify the nonpathological axial stretching in the retinal vascular plexus in three-dimensional (3D) optical coherence tomography angiography (OCTA) images.

Methods

The 3D vascular network underneath the inner limiting membrane of OCTA volumes was labeled as ground truth (GT) data. To analyze the cross-section area of the vessels the width and depth of the vessels in the GT data were computed and an elliptical quotient was proposed to quantify the axial stretching.

Results

A total of 21 3D OCTA volumes were labeled. It was found that the vessels in 3D OCTA images are stretched in the direction of the A-Scan by a factor of 2.46 ± 1.82 with a median of 2.24. Furthermore, a larger cross-section area leads to higher axial stretching.

Conclusions

The elliptical shape of the cross-section area of the vessel does not match with the expected pathology of the vascular network in the human eye. Therefore a correction of the volume data before a 3D analysis is recommended.

Translational Relevance

This work gives a systematic insight to the stretched shape of vessels in 3D OCTA images and is relevant for further clinical research analyzing the 3D vascular network.

Depth-resolved vascular profile features for artery-vein classification in OCT and OCT angiography of human retina

This study is to characterize reflectance profiles of retinal blood vessels in optical coherence tomography (OCT), and to test the potential of using these vascular features to guide artery-vein classification in OCT angiography (OCTA) of the human retina. Depth-resolved OCT reveals unique features of retinal arteries and veins. Retinal arteries show hyper-reflective boundaries at both upper (inner side towards the vitreous) and lower (outer side towards the choroid) walls. In contrast, retinal veins reveal hyper-reflectivity at the upper boundary only. Uniform lumen intensity was observed in both small and large arteries. However, the venous lumen intensity was dependent on the vessel size. Small veins exhibit a hyper-reflective zone at the bottom half of the lumen, while large veins show a hypo-reflective zone at the bottom half of the lumen.

Towards a Clinically Optimized Tilt Mechanism for Bilateral Micromanipulation with Steady-Hand Eye Robot

Cooperative robotic systems for vitreoretinal surgery can enable novel surgical approaches by allowing the surgeon to perform procedures with enhanced stabilization and high accuracy tool movements. This paper presents the optimization and design of a four-bar linkage type tilt mechanism for a novel Steady-Hand Eye Robot (SHER) which can be used equivalently on both, the left and right patient side, during a bilateral approach with two robots. In this optimization, it is desirable to limit the workspace needed for compensation motions that ensure a virtual remote center of motion (V-RCM). The safety space around the patient, the space for the surgeon's hand and maintaining positional accuracy are also included in the optimization. The applicability of the resulting optimized mechanism was confirmed with a design prototype in a representative mock-up of the surgical setting allowing multiple directions of robot approach towards a medical phantom.

Force-based Safe Vein Cannulation in Robot-assisted Retinal Surgery: A Preliminary Study

Retinal vein cannulation (RVC) is a potential treatment for retinal vein occlusion (RVO). Manual surgery has limitations in RVC due to extremely small vessels and instruments involved, as well as the presence of physiological hand tremor. Robot-assisted retinal surgery may be a better approach to smooth and accurate instrument manipulation during this procedure. Motion of the retina and cornea related to heartbeat may be associated with unexpected forces between the tool and eyeball. In this paper, we propose a force-based control strategy to automatically compensate for the movement of the retina maintaining the tip force and sclera force in a predetermined small range. A dual force-sensing tool is used to monitor the tip force, sclera force and tool insertion depth, which will be used to derive a desired joint velocity for the robot via a modified admittance controller. Then the tool is manipulated to compensate for the movement of the retina as well as reduce the tip force and sclera force. Quantitative experiments are conducted to verify the efficacy of the control strategy and a user study is also conducted by a retinal surgeon to demonstrate the advantages of our automatic compensation approach.

Polarization properties of retinal blood vessel walls measured with polarization sensitive optical coherence tomography

A new method based on polarization-sensitive optical coherence tomography (PS-OCT) is introduced to determine the polarization properties of human retinal vessel walls, in vivo. Measurements were obtained near the optic nerve head of three healthy human subjects. The double pass phase retardation per unit depth (DPPR/UD), which is proportional to the birefringence, is higher in artery walls, presumably because of the presence of muscle tissue. Measurements in surrounding retinal nerve fiber layer tissue yielded lower DPPR/UD values, suggesting that the retinal vessel wall tissue near the optic nerve is not covered by retinal nerve fiber layer tissue (0.43°/µm vs. 0.77°/µm, respectively). Measurements were obtained from multiple artery-vein pairs, to quantify the different polarization properties. Measurements were taken along a section of the vessel wall, with changes in DPPR/UD up to 15%, while the vessel wall thickness remained relatively constant. A stationary scan pattern was applied to determine the influence of involuntary eye motion on the measurement, which was significant. Measurements were also analyzed by two examiners, with high inter-observer agreement. The measurement repeatability was determined with measurements that were acquired during multiple visits. An improvement in accuracy can be achieved with an ultra-broad-bandwidth PS-OCT system since it will provide more data points in-depth, which reduces the influence of discretization and helps to facilitate better fitting of the birefringence data.

Retinal Vascular Signs and Cerebrovascular Diseases

BACKGROUND

Cerebrovascular disease (CeVD), including stroke, is a leading cause of death globally. The retina is an extension of the cerebrum, sharing embryological and vascular pathways. The association between different retinal signs and CeVD has been extensively evaluated. In this review, we summarize recent studies which have examined this association.

EVIDENCE ACQUISITION

We searched 6 databases through July 2019 for studies evaluating the link between retinal vascular signs and diseases with CeVD. CeVD was classified into 2 groups: clinical CeVD (including clinical stroke, silent cerebral infarction, cerebral hemorrhage, and stroke mortality), and sub-clinical CeVD (including MRI-defined lacunar infarct and white matter lesions [WMLs]). Retinal vascular signs were classified into 3 groups: classic hypertensive retinopathy (including retinal microaneurysms, retinal microhemorrhage, focal/generalized arteriolar narrowing, cotton-wool spots, and arteriovenous nicking), clinical retinal diseases (including diabetic retinopathy [DR], age-related macular degeneration [AMD], retinal vein occlusion, retinal artery occlusion [RAO], and retinal emboli), and retinal vascular imaging measures (including retinal vessel diameter and geometry). We also examined emerging retinal vascular imaging measures and the use of artificial intelligence (AI) deep learning (DL) techniques.

RESULTS

Hypertensive retinopathy signs were consistently associated with clinical CeVD and subclinical CeVD subtypes including subclinical cerebral large artery infarction, lacunar infarction, and WMLs. Some clinical retinal diseases such as DR, retinal arterial and venous occlusion, and transient monocular vision loss are consistently associated with clinical CeVD. There is an increased risk of recurrent stroke immediately after RAO. Less consistent associations are seen with AMD. Retinal vascular imaging using computer assisted, semi-automated software to measure retinal vascular caliber and other parameters (tortuosity, fractal dimension, and branching angle) has shown strong associations to clinical and subclinical CeVD. Other new retinal vascular imaging techniques (dynamic retinal vessel analysis, adaptive optics, and optical coherence tomography angiography) are emerging technologies in this field. Application of AI-DL is expected to detect subclinical retinal changes and discrete retinal features in predicting systemic conditions including CeVD.

CONCLUSIONS

There is extensive and increasing evidence that a range of retinal vascular signs and disease are closely linked to CeVD, including subclinical and clinical CeVD. New technology including AI-DL will allow further translation to clinical utilization.

Optical Coherence Tomography Angiography and Structural Analyses of the Pale Optic Discs: Is It Possible to Differentiate the Cause?

Introduction: To compare the optic nerve head (ONH) structure and microvasculature in patients with optic atrophy due to non-arteritic anterior ischemic optic neuropathy (NAION), compressive optic neuropathy (CON), methanol-induced optic neuropathy (MION), and traumatic optic neuropathy (TON) using optical coherence tomography angiography.Methods: In this comparative, cross-sectional study, 32 eyes with NAION, 18 eyes with CON, 32 eyes with MION, 23 eyes with TON, and 55 normal eyes were enrolled. Radial peripapillary capillary (RPC) vessel density, peripapillary retinal nerve fiber layer (RNFL) thickness, disc area, cup volume, and cup/disc area ratio were obtained using the RTVue XR Avanti system (Optovue Inc., Fremont, CA, USA).Results: RPC vessel density and peripapillary RNFL thickness in all patients were significantly lower than normal subjects. A positive correlation was found between the RPC vessel density and peripapillary RNFL thickness in normal subjects and all study groups. The positive correlation between the inside and outside disc RPC vessel density was only found in the NAION (r = 0.36, P = .042) and MION (r = 0.42, P = .018) groups. No significant difference was found among the groups in terms of peripapillary and inside disc vascular densities (all P > .05). Disc area and cup volume in patients with MION was larger than the values in patients with NAION (P = .018) and TON (P = .044) and normal subjects (P = .015). The discriminating features among the study groups were the larger cup volume and cup/disc area ratio in patients with MION, and lower RNFL thickness in patients with TON.Conclusions: There was a positive correlation between the RNFL thickness and peripapillary RPC vessel density regardless of the cause of optic disc pallor. Structural evaluation of the ONH seems to be a better way to differentiate the cause of optic nerve head atrophy than the microangiographic changes.

Vascular morphology and blood flow signatures for differential artery-vein analysis in optical coherence tomography of the retina

Differential artery-vein (AV) analysis is essential for retinal study, disease detection, and treatment assessment. This study is to characterize vascular reflectance profiles and blood flow patterns of retinal artery and vein systems in optical coherence tomography (OCT) and OCT angiography (OCTA), and establish them as robust signatures for objective AV classification. A custom designed OCT was employed for three-dimensional (3D) imaging of mouse retina, and corresponding OCTA was reconstructed. Radially resliced OCT B-scans revealed two, i.e. top and bottom, hyperreflective wall boundaries in retinal arteries, while these wall boundaries were absent in OCT of retinal veins. Additional OCTA analysis consistently displayed a layered speckle distribution in the vein, which may indicate the venous laminar flow. These OCT and OCTA differences offer unique signatures for objective AV classification in OCT and OCTA.

Reference values of retinal microcirculation parameters derived from a population random sample

Retinal microcirculation reflects retinal perfusion abnormalities and retinal arterial structural changes at relatively early stages of various cardiovascular diseases. Our objective has been to establish reference values for major functional and structural parameters of retinal microcirculation in a randomly selected urban population sample. A total of 398 randomly selected individuals from an urban population aged 25 to 65 years, resident in Pilsen, Czech Republic, were screened for major cardiovascular risk factors. Retinal microcirculation was assessed using scanning laser Doppler flowmetry (SLDF), with data evaluable in 343 patients. Of this number, complete data were available for 256 individuals free from manifest cardiovascular disease, diabetes and drug treatment for hypertension and/or dyslipidemia, constituting the reference value population. Juxtapapillary retinal capillary blood flow has increased significantly with age whereas vessel and luminal diameters have decreased. No sex differences in retinal microcirculation parameters have been found. Therefore, reference values for retinal microcirculation parameters have been established by age groups. Unattended automated office systolic BP, after adjusting for age, correlated significantly with wall-to-lumen ratio (WLR) and wall thickness (WT). Moreover, after adjusting for age and mean BP, a positive relationship has been found between carotid femoral pulse wave velocity and WT, WLR and wall cross-sectional area, indicating the interaction between micro- and macro-vasculature. In conclusion, our study is the first to provide reference values of retinal microcirculation parameters in a random Caucasian population sample. Our results have shown that, at the population level, the first structural changes in retinal microcirculation are those in lumen diameters. Of note, a close relationship between BP and vascular remodeling of retinal arterioles and between aortic stiffness and WLR of retinal arterioles suggests an interaction between micro- and macro-vasculature.

An Optimized Tilt Mechanism for a New Steady-Hand Eye Robot

Robot-assisted vitreoretinal surgery can filter surgeons' hand tremors and provide safe, accurate tool manipulation. In this paper, we report the design, optimization, and evaluation of a novel tilt mechanism for a new Steady-Hand Eye Robot (SHER). The new tilt mechanism features a four-bar linkage design and has a compact structure. Its kinematic configuration is optimized to minimize the required linear range of motion (LRM) for implementing a virtual remote center-of-motion (V-RCM) while tilting a surgical tool. Due to the different optimization constraints for the robots at the left and right sides of the human head, two configurations of this tilt mechanism are proposed. Experimental results show that the optimized tilt mechanism requires a significantly smaller LRM (e.g. 5.08 mm along Z direction and 8.77 mm along Y direction for left side robot) as compared to the slider-crank tilt mechanism used in the previous SHER (32.39 mm along Z direction and 21.10 mm along Y direction). The feasibility of the proposed tilt mechanism is verified in a mock bilateral robot-assisted vitreoretinal surgery. The ergonomically acceptable robot postures needed to access the surgical field is also determined.

Plane-Wave Ultrasound Doppler of the Eye in Preeclampsia

Purpose

Pre-eclampsia (PE) is a serious complication of pregnancy characterized by high blood pressure, proteinuria, compromised fetal blood supply, and potential organ damage. The superficial location of the eye makes it an ideal target for characterization hemodynamics. Our aim was to discern the impact of PE on ocular blood flow.

Methods

18 MHz plane-wave ophthalmic ultrasound scanning was performed on subjects with PE (n = 26), chronic or gestational hypertension (n = 8), and normal controls (n = 19) within 72 hours of delivery. Duplicate three-second long scans of the posterior pole including the optic nerve were acquired at 6000 images/sec for evaluation of the central retinal artery and vein and the short posterior ciliary arteries. The choroid was scanned at 1000 images/sec. Doppler analysis provided values of pulsatile flow velocity and resistance indexes.

Results

End diastolic velocity was higher, and pulsatility and resistive indexes were significantly lower in the choroid, central retinal artery and short posterior ciliary arteries in PE than in controls. Blood pressure was elevated in PE with respect to controls and was negatively correlated with resistance.

Conclusions

Although vasoconstriction is considered characteristic of PE, we found reduced resistance in the orbital vessels and choroidal arterioles, implying vasodilation at this level. Future studies incorporating optical coherence tomography angiography for characterization of the retina and choriocapillaris in conjunction with plane-wave ultrasound scanning, particularly in late pregnancy, might address this conundrum.

Translational Relevance

Use of plane-wave ultrasound scanning for evaluation ocular blood flow in women at risk for PE may offer an avenue towards early detection and clinical intervention.

Optical coherence tomography-based assessment of retinal vascular pathology in cerebral small vessel disease

Background

Cerebral small vessel disease (CSVD) is a disorder of brain vasculature that causes various structural changes in the brain parenchyma, and is associated with various clinical symptoms such as cognitive impairment and gait disorders. Structural changes of brain arterioles cannot be visualized with routine imaging techniques in vivo. However, optical coherence tomography (OCT) is thought to be a “window to the brain”. Thus, retinal vessel parameters may correlate with CSVD characteristic brain lesions and cerebrospinal fluid biomarkers (CSF) of the neuropathological processes in CSVD like endothelial damage, microglial activation and neuroaxonal damage.

Methods

We applied OCT-based assessment of retinal vessels, magnetic resonance imaging (MRI), and CSF biomarker analysis in a monocentric prospective cohort of 24 patients with sporadic CSVD related stroke and cognitive impairment. MRI lesions were defined according to the STandards for ReportIng Vascular changes on nEuroimaging (STRIVE). Biomarkers were assessed using commercially available ELISA kits. Owing to the unavailability of an age-matched control-group lacking MRI-characteristics of CSVD, we compared the retinal vessel parameters in CSVD patients (73.8 ± 8.5 years) with a younger group of healthy controls (51.0 ± 16.0 years) by using an age- and sex-adjusted multiple linear regression analysis model.

Results

Among the parameters measured with OCT, the Wall to Lumen Ratio (WLR) but not Mean Wall Thickness (MWT) of the superior branch of the retinal artery correlated significantly with the volume of white matter hyperintensities on MRI (r_s = − 0.5) and with CSF-levels of Chitinase 3 like 1 protein (r_s = − 0.6), zona occludens 1 protein (r_s = − 0.5) and GFAP (r_s = − 0.4). MWT and WLR were higher in CSVD than in controls (28.9 μm vs. 23.9 μm, p = 0.001 and 0.32 vs. 0.25, p = 0.001).

Conclusions

In this exploratory study, WLR correlated with the volume of white matter hyperintensities, and markers of vascular integrity, microglial activation, and neuroaxonal damage in CSVD. Further prospective studies should clarify whether retinal vessel parameters and CSF biomarkers may serve to monitor the natural course and treatment effects in clinical studies on CSVD.

New Frontiers in Noninvasive Analysis of Retinal Wall-to-Lumen Ratio by Retinal Vessel Wall Analysis

Purpose

To compare measurement of wall-to-lumen ratio (WLR) by means of high-resolution adaptive optics imaging (AO) with intuitive to use retinal vessel wall (VW) analysis (VWA). Moreover, to validate the techniques by comparing WLR of healthy young (HY) with healthy older patients.

Methods

Ten retinal VW images of 13 HY (24 ± 2 years) and 16 healthy older (60 ± 8 years) were obtained with AO and VWA. The average of five measurements of VW, retinal vessel lumen and WLR of a single vessel from AO and VWA were calculated and compared.

Results

WLR of AO and VWA images showed high correlations, r = 0.75, t(27) = 5.98, P < .001, but differed systematically (WLR: VWA, 40 ± 7% and AO, 35 ± 9%; P < .001). Comparable patterns were found for VW and vessel lumen. HY showed significantly lower WLR (AO, 31 ± 8% and VWA, 36 ± 8%) compared with healthy older (AO, 39 ± 9% [P = .012]; VWA, 42 ± 5% [P = .013]).

Conclusions

Assessment of WLR by VWA showed a good correlation with laborious analysis of the microstructure by high-resolution AO. Measurement of WLR in different age groups indicated good validity. Deviations in VW, vessel lumen, and WLR between AO and VWA can be explained by systematic differences in image scale and resolution. Future studies are needed to investigate the clinical relevance of microvascular WLR assessment by retinal VWA and its prognostic value.

Translational Relevance

Additional assessment of retinal WLR by use of digital VWA to evaluate microstructural remodeling may prove to be a valuable extension to the current use of retinal vessel diameters as biomarkers of cardiovascular risk.

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.

Relative Contributions of Intracranial Pressure and Intraocular Pressure on Lamina Cribrosa Behavior

Purpose

To characterize the relative contributions of intraocular pressure (IOP) and intracranial pressure (ICP) on lamina cribrosa (LC) behavior, specifically LC depth (LCD) and LC peak strain.

Methods

An axially symmetric finite element model of the posterior eye was constructed with an elongated optic nerve and retro-orbital subarachnoid space ensheathed by pia and dura mater. The mechanical environment in LC was evaluated with ICP ranging from 5 to 15 mmHg and IOP from 10 to 45 mmHg. LCD and LC peak strains at various ICP and IOP levels were estimated using full factorial experiments. Multiple linear regression analyses were then applied to estimate LCD and LC peak strain using ICP and IOP as independent variables.

Results

Both increased ICP and decreased IOP led to a smaller LCD and LC peak strain. The regression correlation coefficient for LCD was -1.047 for ICP and 1.049 for IOP, and the ratio of the two regression coefficients was -1.0. The regression correlation coefficient for LC peak strain was -0.025 for ICP and 0.106 for IOP, and the ratio of the two regression coefficients was -0.24. A stiffer sclera increased LCD but decreased LC peak strain; besides, it increased the relative contribution of ICP on the LCD but decreased that on the LC peak strain.

Conclusions

ICP and IOP have opposing effects on LCD and LC peak strain. While their effects on LCD are equivalent, the effect of IOP on LC peak strain is 3 times larger than that of ICP. The influences of these pressure are dependent on sclera material properties, which might explain the pathogenesis of ocular hypertension and normal-tension glaucoma.

Comparative Study of Optical Coherence Tomography Angiography and Phase-Resolved Doppler Optical Coherence Tomography for Measurement of Retinal Blood Vessels Caliber

PURPOSE

To compare the accuracy of Doppler optical coherence tomography (DOCT) and OCT angiography (OCTA) for measuring retinal blood vessel caliber at different flow rates.

METHODS

A research-grade 1060-nm OCT system with 3.5-μm axial resolution in retinal tissue and 92,000 A scan/s image acquisition rate was used in this study. DOCT and OCTA measurements were acquired both from a flow phantom and in vivo from retinal blood vessels in six male Brown Norway rats. The total retinal blood flow (TRBF) was modified from baseline to 70% and 20% of baseline by reducing the ocular perfusion pressure (OPP). The retinal blood vessel caliber (RBVC) was measured from OCTA and DOCT images. The caliber measurements were conducted by two separate graders using a custom MATLAB-based image processing algorithm.

RESULTS

The RBVC measured with OCTA and DOCT for normal blood flow rates were not significantly different (56.69 ± 12.17 and 57.17 ± 9.46 μm, P = 0.27, respectively). However, significant differences were detected when TRBF was reduced to 70% (55.69 ± 11.56 vs. 50.62 ± 8.85 μm, P < 0.01) and 20% (50.29 ± 9.29 vs. 44.88 ± 7.13 μm, P < 0.01) of baseline.

CONCLUSIONS

Reduced TRBF resulted in inaccuracy of the RBVC measurements with DOCT in both the phantom and animal study. This result suggests that OCTA is a more accurate tool for RBVC evaluation when applied to retinal diseases associated with reduced TRBF, such as glaucoma and diabetic retinopathy.

TRANSLATIONAL RELEVANCE

Results from this study are directly applicable to clinical studies of retinal blood flow measured with OCTA and DOCT.

In vivo assessment of retinal vessel pathology in amyotrophic lateral sclerosis

BACKGROUND

Changes in skin and muscle small blood vessels (SBVs) and microvascular structures of the brain have been reported in patients with amyotrophic lateral sclerosis (ALS). A direct assessment of brain SBVs in vivo is currently not feasible. Retinal vessels are considered a "mirror" of brain SBVs. In this study, we used optic coherence tomography (OCT)-based measurements to detect changes in retinal blood vessels of ALS patients compared to those of healthy controls.

METHODS

We analysed Spectralis-OCT images of 34 ALS patients and 20 HCs. The inner wall thickness (IWT), outer wall thickness (OWT), and lumen diameter (LD) of retinal vessels were assessed using intensity-based measurements. In addition, the different retinal layers were analysed using automated segmentation software. The correlations between the various retinal layers and clinical parameters [e.g., disease duration and revised ALS functional rating scale (ALS-FRS-R)] were examined.

RESULTS

The OWT of retinal vessels was higher in ALS patients than in HCs (p = 0.04). There were no differences in the IWT, LD. ALS patients showed a thinning of the outer nuclear layer (ONL) compared to HCs (median 1.63 vs. 1.77, p = 0.002). The whole retinal thickness negatively correlated with the ALS-FRS scale (r = 0.3, p = 0.03).

CONCLUSION

Our study reports retinal vessel pathology in ALS patients. These changes may be related to those observed in SBVs in skin and muscle biopsies. Furthermore, we report a thinning of the ONL in ALS, revealing a possible affection of rods and cones function in ALS.

Hypertension and the eye

PURPOSE OF REVIEW

Hypertension is the primary risk factor for cardiovascular disease and mortality that consists a major public health issue worldwide. Hypertension triggers a series of pathophysiological ocular modifications affecting significantly the retinal, choroidal, and optic nerve circulations that result in a range of ocular effects.The retina is the only place in the body where microvasculature can be directly inspected, providing valuable information on hypertension related systemic risks.The aim of this review is to provide an update on latest advances regarding the detection and significance of hypertension related eye signs.

RECENT FINDINGS

It's been shown that measurable retinal microvascular changes may precede progression of systemic microvascular disease.Last years, there are emerging advances in the field retinal imaging and computer software analysis that have enabled the objective and accurate assessment of retinal vascular caliber, while in association with latest epidemiological studies several other retinal vascular features have been recognized, such as vascular length-to-diameter ratio, and wall-to-lumen ratio that may also be associated to hypertension.Additionally, recent genetic studies have provided some insight to vascular pathophysiological processes having correlated new chromosome's loci to hypertensive retinopathy signs.

SUMMARY

Assessment of hypertensive retinopathy signs may convey additional prognostic information on the risk of end-organ damage and may alert for urgent systemic management or even preventive systemic therapies. Further development of retinal vascular imaging and computerized system may provide a significant tool to improve the diagnosis, prognosis, and management of hypertension in clinical practice.

Detection of retinal blood vessel changes in multiple sclerosis with optical coherence tomography

Although retinal vasculitis is common in multiple sclerosis (MS), it is not known if MS is associated with quantitative abnormalities in retinal blood vessels (BVs). Optical coherence tomography (OCT) is suitable for examining the integrity of the anterior visual pathways in MS. In this paper we have compared the size and number of retinal blood vessels in patients with MS, with and without a history of optic neuritis (ON), and control subjects from the cross-sectional retinal images from OCT. Blood vessel diameter (BVD), blood vessel number (BVN), and retinal nerve fiber layer thickness (RNFLT) were extracted from OCT images collected from around the optic nerves of 129 eyes (24 control, 24 MS + ON, 81 MS-ON) of 71 subjects. Associations between blood vessel metrics, MS diagnosis, MS disability, ON, and RNFLT were evaluated using generalized estimating equation (GEE) models. MS eyes had a lower total BVD and BVN than control eyes. The effect was more pronounced with increased MS disability, and persisted in multivariate models adjusting for RNFLT and ON history. Twenty-nine percent (29%) of MS subjects had fewer retinal blood vessels than all control subjects. MS diagnosis, disability, and ON history were not associated with average blood vessel size. The relationship between MS and lower total BVD/BVN is not accounted for by RNFLT or ON. Further study is needed to determine the relationship between OCT blood vessel metrics and qualitative retinal blood vessel abnormalities in MS.