Vessel Sampling and Blood Flow Velocity Distribution With Vessel Diameter for Characterizing the Human Bulbar Conjunctival Microvasculature

Changes in bulbar conjunctival microcirculation and microvasculature during short-term scleral lens wearing and their associated factors

OBJECTIVE

To explore the changes in microcirculation and microvasculature of the bulbar conjunctiva during the short-term wearing of the scleral lenses (ScCL). And investigate the factors affecting the microcirculation and microvasculature of the bulbar conjunctiva.

METHODS

In this prospective cross-sectional study, functional slit lamp biomicroscopy (FSLB) was used to image the ocular surface microcirculation and microvascular images at two different sites (under the area of ScCL and outside of the area of ScCL) before (baseline) and during the wearing of ScCL at 0 h, 1 h, 2 h and 3 h. Anterior segment optical coherence tomography (AS-OCT) (RTVue, Optovue Inc, USA) was also used to image central post-lens tear film (PoLTF) and the morphology changes of the conjunctiva under the landing zone at the same time period. The semi-automatic quantification of microcirculation and microvasculature including vessel density (Dbox), vessel diameter (D), axial blood flow velocity (Va) and blood flow volume (Q). And the morphological changes of conjunctiva and PoLTF fogging grading were evaluated manually. The changes in the microcirculation and microvasculature of the ocular surface, PoLTF fogging grade and conjunctival morphology were compared before and during the ScCL wearing at different time periods, and the relationship between them was analyzed.

RESULTS

Nineteen eyes (11 right eyes, 8 left eyes) were analyzed in this study. Outside of the area of ScCL, the Dbox before wearing lenses was less than that at 0 h (P = 0.041). The Q at baseline was greater than that after 1 h ScCL wearing (P = 0.026). Under the area of the ScCL, the Q at 1 h was less than that at baseline and 3 h. During the ScCL wearing, statistically significant conjunctival morphology changes were found among different time stages (baseline (0 μm), 0 h (113.18 μm), 2 h (138.97 μm), 3 h (143.83 μm) (all P ＜0.05). Outside the area of the ScCL, the morphology changes of the conjunctiva were negatively correlated with the changes of Va (P＜0.001,r = -0.471) and Q (P = 0.003,r = -0.348),but positively correlated with the Dbox (P = 0.001,r = 0.386). Under the area of ScCL, the morphology changes of the conjunctiva were negatively correlated with the Q (P = 0.012, r = -0.291). The fogging grade was positively correlated with the Q under the area of the ScCL (P = 0.005, r = 0.331).

CONCLUSIONS

The microcirculation and microvasculature of the ocular surface and conjunctival morphology were changed after wearing ScCL in wearers, which indicated that the microvascular responses happened in the ScCL wearers and the severity of microvascular responses of the ocular surface related to the morphology changes of the conjunctiva. The quantification methods and findings in this study provide clues for the safety of ScCL wearing and may supervise the health of the wearer's ocular surface.

Association between dryness sensation and ocular surface temperature and conjunctival blood flow in soft contact lens wearers

PURPOSE

To investigate the association between dryness, ocular surface temperature (OST), and conjunctival blood flow (CBF) in soft contact lens (SCL) wearers after airflow stimulation.

METHODS

After recruiting 21 SCL wearers (mean age, 25.3 ± 4.2 years), subjects used two different daily disposable silicone hydrogel SCLs (narafilcon A and delefilcon A lenses). On three of four measurement days, excluding the first, OST, CBF, tear meniscus height (TMH), and non-invasive tear break-up time (NIBUT) were measured after airflow stimulation at a rate of 3 m/s for 10 min. The measurements were conducted without SCLs on the first and second days, and with different SCLs on the third and fourth days. Dryness was evaluated using the visual analogue scale (VAS). These parameters were compared between the two types of SCLs, and their association with the dryness sensation was then investigated.

RESULTS

Dryness was significantly weakly correlated with OST (r = -0.375, p < 0.05) and CBF (r = 0.339, p < 0.05). TMH, NIBUT, and VAS scores for dryness with the delefilcon A lens (0.15 ± 0.05 mm, 3.7 ± 01.7 s and 29.4 ± 16.9) were significantly higher, longer, and lower, respectively, than those with the narafilcon A lens (0.12 ± 0.05 mm, 2.3 ± 1.7 s and 35.9 ± 17.0; p < 0.05, p < 0.01 and p < 0.01). The changes in the OST and CBF between with and without the delefilcon A lens (-0.36 ± 0.35 °C and 0.99 ± 0.19) were significantly small compared to the narafilcon A lens (-0.60 ± 0.42 °C and 1.11 ± 0.21; p < 0.01 for both comparisons).

CONCLUSION

Dryness was correlated with OST and CBF, which indicates that when dryness was high, OST was low and CBF was high. These results suggest that OST and CBF assessments are effective for evaluating dryness sensation.

Computational analysis of cancer cell adhesion in curved vessels affected by wall shear stress for prediction of metastatic spreading

Introduction: The dynamics of circulating tumor cells (CTCs) within blood vessels play a pivotal role in predicting metastatic spreading of cancer within the body. However, the limited understanding and method to quantitatively investigate the influence of vascular architecture on CTC dynamics hinders our ability to predict metastatic process effectively. To address this limitation, the present study was conducted to investigate the influence of blood vessel tortuosity on the behaviour of CTCs, focusing specifically on establishing methods and examining the role of shear stress in CTC-vessel wall interactions and its subsequent impact on metastasis. Methods: We computationally simulated CTC behaviour under various shear stress conditions induced by vessel tortuosity. Our computational model, based on the lattice Boltzmann method (LBM) and a coarse-grained spectrin-link membrane model, efficiently simulates blood plasma dynamics and CTC deformability. The model incorporates fluid-structure interactions and receptor-ligand interactions crucial for CTC adhesion using the immersed boundary method (IBM). Results: Our findings reveal that uniform shear stress in straight vessels leads to predictable CTC-vessel interactions, whereas in curved vessels, asymmetrical flow patterns and altered shear stress create distinct adhesion dynamics, potentially influencing CTC extravasation. Quantitative analysis shows a 25% decrease in the wall shear stress in low-shear regions and a 58.5% increase in the high-shear region. We observed high-shear regions in curved vessels to be potential sites for increased CTC adhesion and extravasation, facilitated by elevated endothelial expression of adhesion molecules. This phenomenon correlates with the increased number of adhesion bonds, which rises to approximately 40 in high-shear regions, compared to around 12 for straight vessels and approximately 5-6 in low-shear regions. The findings also indicate an optimal cellular stiffness necessary for successful CTC extravasation in curved vessels. Discussion: By the quantitative assessment of the risk of CTC extravasation as a function of vessel tortuosity, our study offers a novel tool for the prediction of metastasis risk to support the development of personalized therapeutic interventions based on individual vascular characteristics and tumor cell properties.

Development of a perfusable, hierarchical microvasculature-on-a-chip model

Several methods have been developed for generating 3D, in vitro, organ-on-chip models of human vasculature to study vascular function, transport, and tissue engineering. However, many of these existing models lack the hierarchical nature of the arterial-to-capillary-to-venous architecture that is key to capturing a more comprehensive view of the human microvasculature. Here, we present a perfusable, multi-compartmental model that recapitulates the three microvascular compartments to assess various physiological properties such as vessel permeability, vasoconstriction dynamics, and circulating cell arrest and extravasation. Viscous finger patterning and passive pumping create the larger arterial and venular lumens, while the smaller diameter capillary bed vessels are generated through self-assembly. These compartments anastomose and form a perfusable, hierarchical system that portrays the directionality of blood flow through the microvasculature. The addition of collagen channels reduces the apparent permeability of the central capillary region, likely by reducing leakage from the side channels, enabling more accurate measurements of vascular permeability-an important motivation for this study. Furthermore, the model permits modulation of fluid flow and shear stress conditions throughout the system by using hydrostatic pressure heads to apply pressure differentials across either the arteriole or the capillary. This is a pertinent system for modeling circulating tumor or T cell dissemination and extravasation. Circulating cells were found to arrest in areas conducive to physical trapping or areas with the least amount of shear stress, consistent with hemodynamic or mechanical theories of metastasis. Overall, this model captures more features of human microvascular beds and is capable of testing a broad variety of hypotheses.

Conjunctival microcirculation in ocular and systemic microvascular disease

The conjunctival microcirculation is an accessible complex network of micro vessels whose quantitative assessment can reveal microvascular haemodynamic properties. Currently, algorithms for the measurement of conjunctival haemodynamics use either manual or semi-automated systems, which may provide insight into overall conjunctival health, as well as in ocular and systemic disease. These algorithms include functional slit-lamp biomicroscopy, laser doppler flowmetry, optical coherence tomography angiography, orthogonal polarized spectral imaging, computer-assisted intravitral microscopy, diffuse reflectance spectroscopy and corneal confocal microscopy. Furthermore, several studies have demonstrated a relationship between conjunctival microcirculatory haemodynamics and many diseases such as dry eye disease, Alzheimer's disease, diabetes, hypertension, sepsis, coronary microvascular disease, and sickle cell anaemia. This review aims to describe conjunctival microcirculation, its characteristics, and techniques for its measurement, as well as the association between conjunctival microcirculation and microvascular abnormalities in disease states.

A normative blood velocity model in the exchange microvessels for discriminating health from disease: Healthy controls versus COVID-19 cases

A usual practice in medicine is to search for "biomarkers" which are measurable quantities of a normal or abnormal biological process. Biomarkers can be biochemical or physical quantities of the body and although commonly used statistically in clinical settings, it is not usual for them to be connected to basic physiological models or equations. In this work, a normative blood velocity model framework for the exchange microvessels was introduced, combining the velocity-diffusion (V-J) equation and statistics, in order to define the normative range (NR) and normative area (NA) diagrams for discriminating normal (normemic) from abnormal (hyperemic or underemic) states, taking into account the microvessel diameter D. This is different from the usual statistical processing since there is a basis on the well-known physiological principle of the flow diffusion equation. The discriminative power of the average axial velocity model was successfully tested using a group of healthy individuals (Control Group) and a group of post COVID-19 patients (COVID-19 Group).

Time-domain ultrasound as prior information for frequency-domain compressive ultrasound for intravascular cell detection: A 2-cell numerical model

This study proposes a new method for the detection of a weak scatterer among strong scatterers using prior-information ultrasound (US) imaging. A perfect application of this approach is in vivo cell detection in the bloodstream, where red blood cells (RBCs) serve as identifiable strong scatterers. In vivo cell detection can help diagnose cancer at its earliest stages, increasing the chances of survival for patients. This work combines time-domain US with frequency-domain compressive US imaging to detect a 20-μ MCF-7 circulating tumor cell (CTC) among a number of RBCs within a simulated venule inside the mouth. The 2D image reconstructed from the time-domain US is employed to simulate the reflected and scattered pressure field from the RBCs, which is then measured at the location of the receivers. The RBCs are tagged one time by a human operator and another time, automatically, by template-based computer vision. Next, the resulting signal from the RBCs is subtracted from the measured total signal in frequency domain to generate the scattered-field data, coming from the CTC alone. Feeding that signal and the background pressure field into a norm-one-based compressive sensing code enables detecting the CTC at various locations. As errors could arise in determining the location of the RBCs and their acoustic properties in the real world, small errors (up to 10% in the former and 5% in the latter) are purposefully introduced to the model, to which the proposed method is shown to be resilient. Localization errors are smaller than 12 μ when a human tags the RBCs and smaller than 25 μ when computer vision is applied. Despite its limitations, this study, for the first time, reports the results of combining two US modalities aimed at cell detection and introduces a unique and useful application for ultrahigh-frequency US imaging. It should be noted that this method can be used in detecting weak scatterers with ultrasound waves in other applications as well.

The potential role of ischaemia-reperfusion injury in chronic, relapsing diseases such as rheumatoid arthritis, Long COVID, and ME/CFS: evidence, mechanisms, and therapeutic implications

Ischaemia-reperfusion (I-R) injury, initiated via bursts of reactive oxygen species produced during the reoxygenation phase following hypoxia, is well known in a variety of acute circumstances. We argue here that I-R injury also underpins elements of the pathology of a variety of chronic, inflammatory diseases, including rheumatoid arthritis, ME/CFS and, our chief focus and most proximally, Long COVID. Ischaemia may be initiated via fibrin amyloid microclot blockage of capillaries, for instance as exercise is started; reperfusion is a necessary corollary when it finishes. We rehearse the mechanistic evidence for these occurrences here, in terms of their manifestation as oxidative stress, hyperinflammation, mast cell activation, the production of marker metabolites and related activities. Such microclot-based phenomena can explain both the breathlessness/fatigue and the post-exertional malaise that may be observed in these conditions, as well as many other observables. The recognition of these processes implies, mechanistically, that therapeutic benefit is potentially to be had from antioxidants, from anti-inflammatories, from iron chelators, and via suitable, safe fibrinolytics, and/or anti-clotting agents. We review the considerable existing evidence that is consistent with this, and with the biochemical mechanisms involved.

Numerical simulation of superparamagnetic nanoparticle motion in blood vessels for magnetic drug delivery

A numerical model is developed for the motion of superparamagnetic nanoparticles in a non-Newtonian blood flow under the influence of a magnetic field. The rheological properties of blood are modeled by the Carreau flow and viscosity, and the stochastic effects of Brownian motion and red blood cell collisions are considered. The model is validated with existing data and good agreement with experimental results is shown. The effectiveness of magnetic drug delivery in various blood vessels is assessed and found to be most successful in arterioles and capillaries. A range of magnetic field strengths are modeled using equations for both a bar magnet and a point dipole: it is shown that the bar magnet is effective at capturing nanoparticles in limited cases, while the point dipole is highly effective across a range of conditions. A parameter study is conducted to show the effects of changing the dipole moment, the distance from the magnet to the blood vessel, and the initial release point of the nanoparticles. The distance from the magnet to the blood vessel is shown to play a significant role in determining nanoparticle capture rate. The optimal initial release position is found to be located within the tumor radius in capillaries and arterioles to prevent rapid diffusion to the edges of the blood vessel prior to arriving at the tumor and near the edge of the magnet when a bar magnet is used.

Identifying diabetes from conjunctival images using a novel hierarchical multi-task network

Diabetes can cause microvessel impairment. However, these conjunctival pathological changes are not easily recognized, limiting their potential as independent diagnostic indicators. Therefore, we designed a deep learning model to explore the relationship between conjunctival features and diabetes, and to advance automated identification of diabetes through conjunctival images. Images were collected from patients with type 2 diabetes and healthy volunteers. A hierarchical multi-tasking network model (HMT-Net) was developed using conjunctival images, and the model was systematically evaluated and compared with other algorithms. The sensitivity, specificity, and accuracy of the HMT-Net model to identify diabetes were 78.70%, 69.08%, and 75.15%, respectively. The performance of the HMT-Net model was significantly better than that of ophthalmologists. The model allowed sensitive and rapid discrimination by assessment of conjunctival images and can be potentially useful for identifying diabetes.

Microfluidic model of monocyte extravasation reveals the role of hemodynamics and subendothelial matrix mechanics in regulating endothelial integrity

Extravasation of circulating cells is an essential process that governs tissue inflammation and the body's response to pathogenic infection. To initiate anti-inflammatory and phagocytic functions within tissues, immune cells must cross the vascular endothelial barrier from the vessel lumen to the subluminal extracellular matrix. In this work, we present a microfluidic approach that enables the recreation of a three-dimensional, perfused endothelial vessel formed by human endothelial cells embedded within a collagen-rich matrix. Monocytes are introduced into the vessel perfusate, and we investigate the role of luminal flow and collagen concentration on extravasation. In vessels conditioned with the flow, increased monocyte adhesion to the vascular wall was observed, though fewer monocytes extravasated to the collagen hydrogel. Our results suggest that the lower rates of extravasation are due to the increased vessel integrity and reduced permeability of the endothelial monolayer. We further demonstrate that vascular permeability is a function of collagen hydrogel mass concentration, with increased collagen concentrations leading to elevated vascular permeability and increased extravasation. Collectively, our results demonstrate that extravasation of monocytes is highly regulated by the structural integrity of the endothelial monolayer. The microfluidic approach developed here allows for the dissection of the relative contributions of these cues to further understand the key governing processes that regulate circulating cell extravasation and inflammation.

Quantification of Blood Flow Velocity in the Human Conjunctival Microvessels Using Deep Learning-Based Stabilization Algorithm

The quantification of blood flow velocity in the human conjunctiva is clinically essential for assessing microvascular hemodynamics. Since the conjunctival microvessel is imaged in several seconds, eye motion during image acquisition causes motion artifacts limiting the accuracy of image segmentation performance and measurement of the blood flow velocity. In this paper, we introduce a novel customized optical imaging system for human conjunctiva with deep learning-based segmentation and motion correction. The image segmentation process is performed by the Attention-UNet structure to achieve high-performance segmentation results in conjunctiva images with motion blur. Motion correction processes with two steps—registration and template matching—are used to correct for large displacements and fine movements. The image displacement values decrease to 4–7 μm during registration (first step) and less than 1 μm during template matching (second step). With the corrected images, the blood flow velocity is calculated for selected vessels considering temporal signal variances and vessel lengths. These methods for resolving motion artifacts contribute insights into studies quantifying the hemodynamics of the conjunctiva, as well as other tissues.

Assessment of the conjunctival microcirculation for patients presenting with acute myocardial infarction compared to healthy controls

Microcirculatory dysfunction occurs early in cardiovascular disease (CVD) development. Acute myocardial infarction (MI) is a late consequence of CVD. The conjunctival microcirculation is readily-accessible for quantitative assessment and has not previously been studied in MI patients. We compared the conjunctival microcirculation of acute MI patients and age/sex-matched healthy controls to determine if there were differences in microcirculatory parameters. We acquired images using an iPhone 6s and slit-lamp biomicroscope. Parameters measured included diameter, axial velocity, wall shear rate and blood volume flow. Results are for all vessels as they were not sub-classified into arterioles or venules. The conjunctival microcirculation was assessed in 56 controls and 59 inpatients with a presenting diagnosis of MI. Mean vessel diameter for the controls was 21.41 ± 7.57 μm compared to 22.32 ± 7.66 μm for the MI patients (p < 0.001). Axial velocity for the controls was 0.53 ± 0.15 mm/s compared to 0.49 ± 0.17 mm/s for the MI patients (p < 0.001). Wall shear rate was higher for controls than MI patients (162 ± 93 s-1 vs 145 ± 88 s-1, p < 0.001). Blood volume flow did not differ significantly for the controls and MI patients (153 ± 124 pl/s vs 154 ± 125 pl/s, p = 0.84). This pilot iPhone and slit-lamp assessment of the conjunctival microcirculation found lower axial velocity and wall shear rate in patients with acute MI. Further study is required to correlate these findings further and assess long-term outcomes in this patient group with a severe CVD phenotype.

Bulbar Conjunctival Microvascular Alterations in Thyroid-Associated Ophthalmopathy Patients with Different Activities

Purpose: To evaluate the morphologic and hemodynamic changes of bulbar conjunctival vessels in thyroid-associated ophthalmopathy (TAO) patients and the correlations with the activity.Methods: Patients diagnosed as TAO with different clinical activity scores (CAS) and healthy participants were recruited. All subjects underwent a complete ophthalmic examination and functional slit-lamp biomicroscope. Vascular variables including the vessel density, vessel complexity, average diameter, blood flow velocity and blood flow rate in microvascular networks were measured. The correlations among microvascular parameters, CAS and exophthalmos were analyzed. Areas under the receiver operating characteristic curves (AUROCs) were applied to evaluate the diagnostic accuracy of microvascular alterations for active TAO.Results: A total of 46 eyes were enrolled in our study. The vessel complexity and blood flow velocity increased in the active TAO group significantly compared with the inactive group and healthy controls (P < .05). Meanwhile, the vessel complexity and blood flow rate were positively correlated with CAS (r = 0.641 and r = 0.526). Bulbar conjunctival microvascular parameters performed a good ability in distinguishing the active stage of TAO (AUROC = 0.793).Conclusions: Increasing bulbar conjunctival vessel complexity and blood flow were evident in TAO with severe inflammation. The measurements of bulbar conjunctival microvasculature could be a reference to evaluate activity in TAO.

Conjunctival Vessels in Diabetes Using Functional Slit Lamp Biomicroscopy

PURPOSE

This study used functional slit lamp biomicroscopy (FSLB) to quantify conjunctival microvessel parameters in individuals with and without diabetes and examined whether these metrics could be used as surrogate markers of diabetes-related complications.

METHODS

A cross-sectional study of 98 controls (C), 13 individuals with diabetes without complications (D-C), and 21 with diabetes and related complications (D+C), which included retinopathy, nephropathy, neuropathy, and cardiovascular-, peripheral vascular-, and cerebrovascular diseases, was performed. Bulbar conjunctival metrics (venule diameter, length, axial velocity [Va], cross-sectional velocity [Vs], flow [Q], and branching complexity) were measured using FSLB (digital camera mounted on traditional slit lamp).

RESULTS

The mean age was 60 ± 11 years, and demographics were similar across the groups. Va and Vs significantly differed between groups. Va was 0.51 ± 0.17 mm/s, 0.62 ± 0.17 mm/s, and 0.45 ± 0.17 mm/s in the C, D-C, and D+C groups, respectively (P = 0.025). Similarly, Vs was 0.35 ± 01.12, 0.43 ± 0.13, and 0.32 ± 0.13 mm/s in the C, D-C, and D+C groups, respectively (P = 0.031). Black individuals had increased Va, Vs, and Q compared with White individuals (P < 0.05), but differences in velocities persisted after accounting for race. Among patients with diabetes, Va and Vs correlated with number of organ systems affected (Va: ρ = -0.42, P = 0.016; Vs: ρ = -0.41, P = 0.021). Va, Vs, and Q significantly (P ≤ 0.005) discriminated between diabetic patients with and without complications (area under the receiver operating curve for Va = 0.81, Vs = 0.79, Q = 0.81).

CONCLUSIONS

Bulbar conjunctival blood flow metrics measured by FSLB differed between controls, diabetic patients without complications, and diabetic patients with complications. FSLB is a quick, easily accessible, and noninvasive alternative that might estimate the burden of vascular complications in diabetes.

Improved conjunctival microcirculation in diabetic retinopathy patients with MTHFR polymorphisms after Ocufolin™ Administration

PURPOSE

To investigate conjunctival microvascular responses in patients with mild diabetic retinopathy (MDR) and methylenetetrahydrofolate reductase (MTHFR) polymorphisms (D + PM) after administration of Ocufolin™, a medical food containing 900 μg l-methylfolate (levomefolate calcium or [6S]-5-methyltetrahydrofolic acid, calcium salt), methylcobalamin, and other ingredients.

METHODS

Eight D + PM patients received Ocufolin™ for six months (6 M). Bulbar conjunctival microvasculature and microcirculation metrics, including vessel diameter (D), axial blood flow velocity (Va), cross-sectional blood flow velocity (Vs), flow rate (Q), and vessel density (VD, Dbox), were measured at baseline, 4 M, and 6 M.

RESULTS

The mean age was 54 ± 7 years. No significant demographic differences were found. Conjunctival microcirculation, measured as Va, Vs, and Q was significantly increased at 4 M and 6 M, compared to baseline. Va was 0.44 ± 0.10 mm/s, 0.58 ± 0.13 mm/s, 0.59 ± 0.13 mm/s in baseline, 4 M, and 6 M, respectively (P < 0.01). Similarly, Vs was 0.31 ± 0.07 mm/s, 0.40 ± 0.09 mm/s, 0.41 ± 0.09 mm/s in baseline, 4 M, and 6 M, respectively (P < 0.05). Q was 107.8 ± 49.4 pl/s, 178.0 ± 125.8 pl/s, 163.3 ± 85.8 mm/s in baseline, 4 M, and 6 M, respectively (P < 0.05). The VD at 6 M was significantly higher than that at baseline (P = 0.017). Changes of D were positively correlated with changes of Va, Q, and VD. Effects of MTHFR and haptoglobin polymorphisms on the improvements of conjunctival microcirculation and microvasculature were found.

CONCLUSIONS

Ocufolin™ supplementation improves conjunctival microcirculation in patients with diabetic retinopathy and common folate polymorphisms.

Conjunctival microvascular responses to anti-inflammatory treatment in patients with dry eye

PURPOSE

This study characterized conjunctival microvascular morphological and haemodynamic responses after anti-inflammatory treatment in dry eye (DE).

MATERIALS AND METHODS

Twenty-five patients with moderate DE (17 females and 8 males aged 48 ± 16 years) who underwent anti-inflammatory therapy (0.1% fluorometholone) and 25 healthy subjects (20 females and 5 males aged 48 ± 17 years) recruited as controls were enrolled. The conjunctival blood flow rate (BFR), blood flow velocity (BFV) and vessel diameter were measured by functional slit-lamp biomicroscopy (FSLB). DE symptoms and signs were assessed. All measurements were performed at baseline and at 30 and 60 days after commencement of treatment.

RESULTS

At baseline, the conjunctival BFR, BFV, and vessel diameter were higher in the DE group than in the control group (p < 0.05). The BFR, BFV and corneal fluorescein staining (CFS) scores decreased at 60 days after therapy compared to at baseline and 30 days (all p_corrected < 0.05); Ocular surface diseases index (OSDI), the hyperaemia index (HI) and vessel diameters only showed significant decreases at 30 days. Moreover, significant increases in the noninvasive tear film break-up time (NI-BUT) and Schirmer I test score (ST) were observed. The CFS score correlated positively with BFV (r = 0.46), BFR (r = 0.58) and vessel diameter (r = 0.47).

CONCLUSION

This study characterized conjunctival microvascular responses to anti-inflammatory treatment in DE patients. The results suggest that conjunctival BFV and BFR can be used as dynamic markers for treatment efficacy in DE.

Multi-modal Anterior Eye Imager Combining Ultra-High Resolution OCT and Microvascular Imaging for Structural and Functional Evaluation of the Human Eye

To establish complementary information for the diagnosis and evaluation of ocular surface diseases, we developed a multi-modal, non-invasive optical imaging platform by combining ultra-high resolution optical coherence tomography (UHR-OCT) with a microvascular imaging system based on slit-lamp biomicroscopy. Our customized UHR-OCT module achieves an axial resolution of ≈2.9 μm in corneal tissue with a broadband light source and an A-line acquisition rate of 24 kHz with a line array CCD camera. The microvascular imaging module has a lateral resolution of 3.5 μm under maximum magnification of ≈187.5× with an imaging rate of 60 frames/s, which is sufficient to image the conjunctival vessel network and record the movement trajectory of clusters of red blood cells. By combining the imaging optical paths of different modules, our customized multi-modal anterior eye imaging platform is capable of performing real-time cross-sectional UHR-OCT imaging of the anterior eye, conjunctival vessel network imaging, high-resolution conjunctival blood flow videography, fluorescein staining and traditional slit-lamp imaging on a single device. With self-developed software, a conjunctival vessel network image and blood flow videography were further analyzed to acquire quantitative morphological and hemodynamics parameters, including vessel fractal dimensions, blood flow velocity and vessel diameters. The ability of our multi-modal anterior eye imager to provide both structural and functional information for ophthalmic clinical applications was demonstrated on a healthy human subject and a keratitis patient.

Quantitative assessment of the conjunctival microcirculation using a smartphone and slit-lamp biomicroscope

PURPOSE

The conjunctival microcirculation is a readily-accessible vascular bed for quantitative haemodynamic assessment and has been studied previously using a digital charge-coupled device (CCD). Smartphone video imaging of the conjunctiva, and haemodynamic parameter quantification, represents a novel approach. We report the feasibility of smartphone video acquisition and subsequent haemodynamic measure quantification via semi-automated means.

METHODS

Using an Apple iPhone 6 s and a Topcon SL-D4 slit-lamp biomicroscope, we obtained videos of the conjunctival microcirculation in 4 fields of view per patient, for 17 low cardiovascular risk patients. After image registration and processing, we quantified the diameter, mean axial velocity, mean blood volume flow, and wall shear rate for each vessel studied. Vessels were grouped into quartiles based on their diameter i.e. group 1 (<11 μm), 2 (11-16 μm), 3 (16-22 μm) and 4 (>22 μm).

RESULTS

From the 17 healthy controls (mean QRISK3 6.6%), we obtained quantifiable haemodynamics from 626 vessel segments. The mean diameter of microvessels, across all sites, was 21.1μm (range 5.8-58 μm). Mean axial velocity was 0.50mm/s (range 0.11-1mm/s) and there was a modestly positive correlation (r 0.322) seen with increasing diameter, best appreciated when comparing group 4 to the remaining groups (p < .0001). Blood volume flow (mean 145.61pl/s, range 7.05-1178.81pl/s) was strongly correlated with increasing diameter (r 0.943, p < .0001) and wall shear rate (mean 157.31 s^-1, range 37.37-841.66 s^-1) negatively correlated with increasing diameter (r - 0.703, p < .0001).

CONCLUSIONS

We, for the first time, report the successful assessment and quantification of the conjunctival microcirculatory haemodynamics using a smartphone-based system.

A review of functional slit lamp biomicroscopy

Functional slit lamp biomicroscopy (FSLB) is a novel device which consists of a traditional slit-lamp and a digital camera. It can quantitatively assess vessel diameter, blood flow velocity, and blood flow rate and can create noninvasive microvascular perfusion maps (nMPMs). At present, FSLB is mainly used in contact lens (CL) and dry eye disease (DED) studies to advance our understanding of ocular surface microcirculation. FSLB-derived blood flow and vessel density measures are significantly altered in CL wearers and DED patients compared to normal people. These subtle changes in the ocular surface microcirculation may contribute to the monitoring of potential diseases of the body and provide a new way to diagnose dry eye disease. Therefore, this may also indicate that FSLB can be more widely applied in the study of other diseases to reveal the relationship between changes in ocular surface microcirculation and systemic diseases. The purpose of this paper is to summarize the functions of FSLB and the related studies especially in CL and DED.

Microcirculation in the conjunctiva and retina in healthy subjects

Background

The aim was to determine the relationship between bulbar conjunctival microcirculation and retinal microcirculation in a healthy population.

Method

A functional slit-lamp biomicroscope (FSLB) was used to measure blood flow velocity (BFV) and blood flow rate (BFR) in the conjunctiva while a retinal function imager (RFI) was used to measure macular BFV and BFR in the retina. One eye of each subject of 58 self-reported healthy subjects was imaged in the same session on the same day.

Results

The mean BFV in the venules of the conjunctiva was 0.49 ± 0.13 mm/s, which was significantly slower than that in the retinal arterioles (3.71 ± 0.78 mm/s, P < 0.001) and retinal venules (2.98 ± 0.58 mm/s, P < 0.001). The BFR in the conjunctiva (0.09 nl/s) was also significantly lower than that in the retina (arterioles = 0.81 nl/s, venules = 0.68 nl/s, all P < 0.001). The BFVs and BFRs were not related between the conjunctiva and retina (r ranged from − 0.17 to − 0.05, all P > 0.05).

Conclusion

The microcirculation in the retina appeared to be different from that in the conjunctiva.

Probing dynamic processes in the eye at multiple spatial and temporal scales with multimodal full field OCT

We describe recent technological progress in multimodal en face full-field optical coherence tomography that has allowed detection of slow and fast dynamic processes in the eye. We show that by combining static, dynamic and fluorescence contrasts we can achieve label-free high-resolution imaging of the retina and anterior eye with temporal resolution from milliseconds to several hours, allowing us to probe biological activity at subcellular scales inside 3D bulk tissue. Our setups combine high lateral resolution over a large field of view with acquisition at several hundreds of frames per second which make it a promising tool for clinical applications and biomedical studies. Its contactless and non-destructive nature is shown to be effective for both following in vitro sample evolution over long periods of time and for imaging of the human eye in vivo.

Functional slit lamp biomicroscopy metrics correlate with cardiovascular risk

PURPOSE

Our aim was to correlate cardiovascular risk factor estimation with bulbar conjunctival blood flow metrics as measured through Functional Slit Lamp Biomicroscopy (FSLB).

METHODS

Cross-sectional study of individuals with otherwise healthy eyelid and corneal anatomy recruited from the Miami Veterans Affairs (VA) Healthcare System eye clinic. We measured conjunctival microvascular hemodynamics by mounting a camera on a slit lamp and cardiovascular risk using the Framingham risk score. Our main outcome measures were correlations between conjunctival vessel parameters (axial and cross-sectional blood flow velocity, blood flow rate) and Framingham score.

RESULTS

We included 84 patients who underwent FSLB. The mean age was 60 years, the majority were male (88%) and approximately half the patients were black (54%). Mean vessel diameter was similar between all Framingham score categories. Axial and cross-sectional blood flow velocities and blood flow rate were lower in individuals with higher Framingham risk score. Specifically, mean cross-sectional blood flow velocity in individuals with a low Framingham risk score was 0.37 ± 0.0.9 mm/s, with an intermediate score was 0.30 ± 0.09 mm/s, and with a high score was 0.29 ± 0.10 mm/s, p = 0.04. Mean blood flow rate in individuals with a low Framingham risk score was 133.4 ± 59.6 pl/s, with an intermediate score was 123.6 ± 39.3 pl/s, and with a high score was 121.9 ± 52.6 pl/s, p = 0.04. The beta coefficient of the blood flow rate for change in Framingham score was -0.73; 95% CI-1.34-0.13, p = 0.02, adjusted for race.

CONCLUSION

FSLB correlates with cardiovascular risk estimation. Future studies should evaluate if FSLB can predict cardiovascular outcomes.

Dynamic Adhesion Assay for the Functional Analysis of Anti-adhesion Therapies in Inflammatory Bowel Disease

Gut homing of immune cells is important for the pathogenesis of inflammatory bowel diseases (IBD). Integrin-dependent cell adhesion to addressins is a crucial step in this process and therapeutic strategies interfering with adhesion have been successfully established. The anti-α4β7 integrin antibody, vedolizumab, is used for the clinical treatment of Crohn's disease (CD) and ulcerative colitis (UC) and further compounds are likely to follow. The details of the adhesion procedure and the action mechanisms of anti-integrin antibodies are still unclear in many regards due to the limited available techniques for the functional research in this field. Here, we present a dynamic adhesion assay for the functional analysis of human cell adhesion under flow conditions and the impact of anti-integrin therapies in the context of IBD. It is based on the perfusion of primary human cells through addressin-coated ultrathin glass capillaries with real-time microscopic analysis. The assay offers a variety of opportunities for refinements and modifications and holds potentials for mechanistic discoveries and translational applications.

Evaluated Conjunctival Blood Flow Velocity in Daily Contact Lens Wearers

OBJECTIVE

This study examined conjunctival microvasculature development in long-term habitual contact lens (HCL) wearers after a night of sleep.

METHODS

Twenty HCL wearers (15 women and 5 men, aged 28.6±6.9 years, mean age±standard deviation) who had worn contact lenses on a daily basis for at least 3 years and 40 noncontact lens (NCL) wearers (23 women and 17 men, aged 36.5±6.6 years, mean age±standard deviation) participated in the study. A functional slitlamp biomicroscopy imaging system was used to image the temporal bulbar conjunctiva. Imaging was performed in the morning while the contact lens wearers were not wearing their lenses after a night of sleep. The conjunctival vessel diameters, blood flow velocities, and flow rates were measured. In addition, fractal analyses were performed to obtain the vessel network density (Dbox) and complexity (D0).

RESULTS

The average blood flow velocity in HCL wearers after a night of sleep was 0.59±0.19 mm/s, which was significantly higher than that in NCL wearers (0.48±0.17 mm/s, P<0.05). The microvessel network density and complexity levels (Dbox=1.64±0.05 and D0=1.71±0.05, respectively) in the HCL wearers were significantly higher than those in NCL wearers (Dbox=1.61±0.05 and D0=1.69±0.04, both P<0.05). The blood flow velocity was positively correlated with the duration of contact lens wear (r=0.46, P<0.05) and with the daily number of lens-wearing hours (r=0.49, P<0.05) in HCL wearers.

CONCLUSIONS

This study identified microvascular alterations in the conjunctiva in response to daily contact lens wear after a night of sleep in long-term daily contact lens wearers. The unrecovered changes may indicate that para-inflammation occurs on ocular surfaces because of contact lens wear and that overnight sleeping with no lenses may not sufficiently restore the ocular surface to an intact state.

Vascular-targeted particle binding efficacy in the presence of rigid red blood cells: Implications for performance in diseased blood

The field of drug delivery has taken an interest in combating numerous blood and heart diseases via the use of injectable vascular-targeted carriers (VTCs). However, VTC technology has encountered limited efficacy due to a variety of challenges associated with the immense complexity of the in vivo blood flow environment, including the hemodynamic interactions of blood cells, which impact their margination and adhesion to the vascular wall. Red blood cell (RBC) physiology, i.e., size, shape, and deformability, drive cellular distribution in blood flow and has been shown to impact VTC margination to the vessel wall significantly. The RBC shape and deformability are known to be altered in certain human diseases, yet little experimental work has been conducted towards understanding the effect of these alterations, specifically RBC rigidity, on VTC dynamics in physiological blood flow. In this work, we investigate the impact of RBCs of varying stiffnesses on the adhesion efficacy of particles of various sizes, moduli, and shapes onto an inflamed endothelial layer in a human vasculature-inspired, in vitro blood flow model. The blood rigid RBC compositions and degrees of RBC stiffness evaluated are analogous to conditions in diseases such as sickle cell disease. We find that particles of different sizes, moduli, and shapes yield drastically different adhesion patterns in blood flow in the presence of rigid RBCs when compared to 100% healthy RBCs. Specifically, up to 50% reduction in the localization and adhesion of non-deformable 2 μm particles to the vessel wall was observed in the presence of rigid RBCs. Interestingly, deformable 2 μm particles showed enhanced vessel wall localization and adhesion, by up to 85%, depending on the rigidity of RBCs evaluated. Ultimately, this work experimentally clarifies the importance of considering RBC rigidity in the intelligent design of particle therapeutics and highlights possible implications for a wide range of diseases relating to RBC deformability.

Altered Bulbar Conjunctival Microcirculation in Response to Contact Lens Wear

PURPOSE

This study was conducted to determine blood flow velocities and corresponding vessel diameters to characterize the response of the bulbar conjunctival microvasculature to contact lens wear.

METHODS

A functional slit-lamp biomicroscope (FSLB), an adapted traditional slitlamp, was used to image the temporal bulbar conjunctiva of 22 healthy subjects before and after 6 hr of contact lens wear. All of the measurable venules on the conjunctiva were processed to yield vessel diameters and blood flow velocities.

RESULTS

The average blood flow velocity increased from 0.51±0.20 to 0.65±0.22 mm/sec (P<0.001) after 6 hr of lens wear. The blood flow velocity distribution showed a velocity increase that correlated with the vessel diameter increase from the baseline (r=0.826, P<0.05). This pattern maintained a similar trend after 6 hr of lens wear (r=0.925, P<0.05), and increased velocities were found across all of the vessel diameter ranges (P<0.001).

CONCLUSIONS

Blood flow velocity increases across all of the vessel diameter ranges in response to contact lens wear. Functional slitlamp biomicroscope is capable of characterizing the bulbar microvascular response to contact lens wear.

Imaging of the Finger Vein and Blood Flow for Anti-Spoofing Authentication Using a Laser and a MEMS Scanner

A new authentication method employing a laser and a scanner is proposed to improve image contrast of the finger vein and to extract blood flow pattern for liveness detection. A micromirror reflects a laser beam and performs a uniform raster scan. Transmissive vein images were obtained, and compared with those of an LED. Blood flow patterns were also obtained based on speckle images in perfusion and occlusion. Curvature ratios of the finger vein and blood flow intensities were found to be nearly constant, regardless of the vein size, which validated the high repeatability of this scheme for identity authentication with anti-spoofing.

Bulbar conjunctival microvascular responses in dry eye

PURPOSE

Conjunctival microvascular responses may be a surrogate metric of efferent neural pathway function innervating the ocular surface as changes in blood flow occur within seconds after a stimulus. As somatosensory dysfunction may partially underlie dry eye (DE), in this study we evaluate whether bulbar conjunctival microvascular alterations correlate with various aspects of DE.

METHODS

Fifty-six DE patients were prospectively recruited from a Veterans Affairs ophthalmology clinic over an 11-month period. DE symptoms and ocular pain were assessed along with DE signs. A novel functional slit lamp biomicroscope (FSLB) was used to image the temporal bulbar conjunctiva from the right eye before and after central corneal stimulation with an air puff. Blood flow velocities were measured and noninvasive microvascular perfusion maps (nMPMs) were created.

RESULTS

The bulbar blood flow velocity was 0.50 ± 0.15 mm/s at baseline and increased to 0.55 ± 0.17 mm/s after stimulation (P < 0.001); the average change in velocity was 0.05 ± 0.09. nMPMs values and venule diameter, on the other hand, did not significantly increase after stimulation (1.64 ± 0.004 at baseline, 1.65 ± 0.04 after stimulation, P = 0.22 and 22.13 ± 1.84 μm at baseline, 22.21 ± 2.04 μm after stimulation, P = 0.73, respectively). Baseline blood flow velocity positively associated with Schirmer scores (r = 0.40, P = 0.002). Those with higher self-rated wind hyperalgesia demonstrated less change in blood flow velocity (r = -0.268, P = 0.046) after air stimulation on the central cornea.

CONCLUSION

Conjunctival blood flow velocity, but not vessel diameter or complexity, increases after wind stimuli. Baseline flow positively correlated with Schirmer scores while change in flow negatively correlated with self-reported wind hyperalgesia.

Automated Real-Time Conjunctival Microvasculature Image Stabilization

The bulbar conjunctiva is a thin, vascularized membrane covering the sclera of the eye. Non-invasive imaging techniques have been utilized to assess the conjunctival vasculature as a means of studying microcirculatory hemodynamics. However, eye motion often confounds quantification of these hemodynamic properties. In the current study, we present a novel optical imaging system for automated stabilization of conjunctival microvasculature images by real-time eye motion tracking and realignment of the optical path. The ability of the system to stabilize conjunctival images acquired over time by reducing image displacements and maintaining the imaging area was demonstrated.

Automated Assessment of Hemodynamics in the Conjunctival Microvasculature Network

The conjunctival microcirculation is accessible for direct visualization and quantitative assessment of microvascular hemodynamic properties. Currently available methods to assess hemodynamics in the conjunctival microvasculature use manual or semi-automated algorithms, which can be inefficient for application to a large number of microvessels within the microvascular network. We present an automated image analysis method for measurements of diameter and blood velocity in microvessels. The method was applied to conjunctival microcirculation images acquired in 15 healthy human subjects. Frangi filtering, thresholding, and morphological closing were applied to automatically segment microvessels, while variance filtering was used to detect blood flow. Diameter and blood velocity were measured in arterioles and venules within the conjunctival microvascular network, and blood flow and wall shear rate were calculated. Repeatability and validity of hemodynamic measurements were established. The automated image analysis method allows reliable, rapid and quantitative assessment of hemodynamics in the conjunctival microvascular network and can be potentially applied to microcirculation images of other tissues.