Feasibility of assessment of conjunctival microvascular hemodynamics in unilateral ischemic stroke

TFOS Lifestyle: Impact of nutrition on the ocular surface

Nutrients, required by human bodies to perform life-sustaining functions, are obtained from the diet. They are broadly classified into macronutrients (carbohydrates, lipids, and proteins), micronutrients (vitamins and minerals) and water. All nutrients serve as a source of energy, provide structural support to the body and/or regulate the chemical processes of the body. Food and drinks also consist of non-nutrients that may be beneficial (e.g., antioxidants) or harmful (e.g., dyes or preservatives added to processed foods) to the body and the ocular surface. There is also a complex interplay between systemic disorders and an individual's nutritional status. Changes in the gut microbiome may lead to alterations at the ocular surface. Poor nutrition may exacerbate select systemic conditions. Similarly, certain systemic conditions may affect the uptake, processing and distribution of nutrients by the body. These disorders may lead to deficiencies in micro- and macro-nutrients that are important in maintaining ocular surface health. Medications used to treat these conditions may also cause ocular surface changes. The prevalence of nutrition-related chronic diseases is climbing worldwide. This report sought to review the evidence supporting the impact of nutrition on the ocular surface, either directly or as a consequence of the chronic diseases that result. To address a key question, a systematic review investigated the effects of intentional food restriction on ocular surface health; of the 25 included studies, most investigated Ramadan fasting (56%), followed by bariatric surgery (16%), anorexia nervosa (16%), but none were judged to be of high quality, with no randomized-controlled trials.

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).

Assessment of hemodynamic indices of conjunctival microvascular function in patients with coronary microvascular dysfunction

OBJECTIVE

Coronary microvascular dysfunction (CMD) is a cause of ischaemia with non-obstructive coronary arteries (INOCA). It is notoriously underdiagnosed due to the need for invasive microvascular function testing. We hypothesized that systemic microvascular dysfunction could be demonstrated non-invasively in the microcirculation of the bulbar conjunctiva in patients with CMD.

METHODS

Patients undergoing coronary angiography for the investigation of chest pain or dyspnoea, with physiologically insignificant epicardial disease (fractional flow reserve ≥0.80) were recruited. All patients underwent invasive coronary microvascular function testing. We compared a cohort of patients with evidence of CMD (IMR ≥25 or CFR <2.0); to a group of controls (IMR <25 and CFR ≥2.0). Conjunctival imaging was performed using a previously validated combination of a smartphone and slit-lamp biomicroscope. This technique allows measurement of vessel diameter and other indices of microvascular function by tracking erythrocyte motion.

RESULTS

A total of 111 patients were included (43 CMD and 68 controls). There were no differences in baseline demographics, co-morbidities or epicardial coronary disease severity. The mean number of vessel segments analysed per patient was 21.0 ± 12.8 (3.2 ± 3.5 arterioles and 14.8 ± 10.8 venules). In the CMD cohort, significant reductions were observed in axial/cross-sectional velocity, blood flow, wall shear rate and stress.

CONCLUSION

The changes in microvascular function linked to CMD can be observed non-invasively in the bulbar conjunctiva. Conjunctival vascular imaging may have utility as a non-invasive tool to both diagnose CMD and augment conventional cardiovascular risk assessment.

Assessment of indices of conjunctival microvascular function in patients with and without obstructive coronary artery disease

BACKGROUND

Atherosclerotic heart disease often remains asymptomatic until presentation with a major adverse cardiovascular event. Primary preventive therapies improve outcomes, but conventional screening often misattributes risk. Vascular imaging can be utilised to detect atherosclerosis, but often involves ionising radiation. The conjunctiva is a readily accessible vascular network allowing non-invasive hemodynamic evaluation.

AIM

To compare conjunctival microcirculatory function in patients with and without obstructive coronary artery disease.

METHODS

We compared the conjunctival microcirculation of myocardial infarction patients (MI-cohort) to controls with no obstructive coronary artery disease (NO-CAD cohort). Conjunctival imaging was performed using a smartphone and slit-lamp biomicroscope combination. Microvascular indices of axial (V_a) and cross-sectional (V_cs) velocity; blood flow rate (Q); and wall shear rate (WSR) were compared in all conjunctival vessels between 5 and 45 μm in diameter.

RESULTS

A total of 127 patients were recruited (66 MI vs 61 NO-CAD) and 3602 conjunctival vessels analysed (2414 MI vs 1188 NO-CAD). Mean V_a, V_cs and Q were significantly lower in the MI vs NO-CAD cohort (V_a 0.50 ± 0.17 mm/s vs 0.55 ± 0.15 mm/s, p < 0.001; V_cs 0.35 ± 0.12 mm/s vs 0.38 ± 0.10 mm/s, p < 0.001; Q 154 ± 116 pl/s vs 198 ± 130 pl/s, p < 0.001). To correct for differences in mean vessel diameter, WSR was compared in 10-36 μm vessels (3268/3602 vessels) and was lower in the MI-cohort (134 ± 64 s^-1 vs 140 ± 63 s^-1, p = 0.002).

CONCLUSIONS

Conjunctival microcirculatory alterations can be observed in patients with obstructive coronary artery disease. The conjunctival microvasculature merits further evaluation in cardiovascular risk screening.

Conjunctival optical coherence tomography angiography imaging in sickle cell maculopathy

Purpose

To compare conjunctival and macular manifestations of sickle cell anemia using optical coherence tomography angiography (OCTA).

Observations

OCTA imaging of the macula in two patients with HbSS and HbSC revealed areas of decreased vascular density, more prominent in the deep capillary plexus than in the superficial capillary plexus. Conjunctival OCTA of both affected patients revealed areas of reduced vascular density corresponding to the vascular abnormalities observed on slit lamp examination and prominent conjunctival flow voids when compared to an unaffected control.

Conclusionsand Importance

OCTA allows for high resolution visualization of conjunctival findings present in sickle cell patients with macular vascular flow voids. Further studies are needed to explore the utility of conjunctival OCTA and the relationship between conjunctival and macular perfusion and systemic hemoglobinopathy.

EVA: Fully automatic hemodynamics assessment system for the bulbar conjunctival microvascular network

BACKGROUND AND OBJECTIVE

Conjunctival microcirculation has been used to quantitatively assess microvascular changes due to systemic disorders. The space between red blood cell clusters in conjunctival microvessels is essential for assessing hemodynamics. However, it causes discontinuities in vessel image segmentation and increases the difficulty of automatically measuring blood velocity. In this study, we developed an EVA system based on deep learning to maintain vessel segmentation continuity and automatically measure blood velocity.

METHODS

The EVA system sequentially performs image registration, vessel segmentation, diameter measurement, and blood velocity measurement on conjunctival images. A U-Net model optimized with a connectivity-preserving loss function was used to solve the problem of discontinuities in vessel segmentation. Then, an automatic measurement algorithm based on line segment detection was proposed to obtain accurate blood velocity. Finally, the EVA system assessed hemodynamic parameters based on the measured blood velocity in each vessel segment.

RESULTS

The EVA system was validated for 23 videos of conjunctival microcirculation captured using functional slit-lamp microscopy. The U-Net model produced the longest average vessel segment length, 158.03 ± 181.87 µm, followed by the adaptive threshold method and Frangi filtering, which produced lengths of 120.05 ± 151.47 µm and 99.94 ± 138.12 µm, respectively. The proposed method and one based on cross-correlation were validated to measure blood velocity for a dataset consisting of 30 vessel segments. Bland-Altman analysis showed that compared with the cross-correlation method (bias: 0.36, SD: 0.32), the results of the proposed method were more consistent with a manual measurement-based gold standard (bias: -0.04, SD: 0.14).

CONCLUSIONS

The proposed EVA system provides an automatic and reliable solution for quantitative assessment of hemodynamics in conjunctival microvascular images, and potentially can be applied to hypoglossal microcirculation images.

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.

Assessment of the conjunctival microcirculation in adult patients with cyanotic congenital heart disease compared to healthy controls

PURPOSE

Congenital heart disease (CHD) is the most common live birth defect and a proportion of these patients have chronic hypoxia. Chronic hypoxia leads to secondary erythrocytosis resulting in microvascular dysfunction and increased thrombosis risk. The conjunctival microcirculation is easily accessible for imaging and quantitative assessment. It has not previously been studied in adult CHD patients with cyanosis (CCHD).

METHODS

We assessed the conjunctival microcirculation and compared CCHD patients and matched healthy controls to determine if there were differences in measured 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. The axial velocity was estimated by applying the 1D + T continuous wavelet transform (CWT). Results are for all vessels as they were not sub-classified into arterioles or venules.

RESULTS

11 CCHD patients and 14 healthy controls were recruited to the study. CCHD patients were markedly more hypoxic compared to the healthy controls (84% vs 98%, p = 0.001). A total of 736 vessels (292 vs 444) were suitable for analysis. Mean microvessel diameter (D) did not significantly differ between the CCHD patients and controls (20.4 ± 2.7 μm vs 20.2 ± 2.6 μm, p = 0.86). Axial velocity (Va) was lower in the CCHD patients (0.47 ± 0.06 mm/s vs 0.53 ± 0.05 mm/s, p = 0.03). Blood volume flow (Q) was lower for CCHD patients (121 ± 30pl/s vs 145 ± 50pl/s, p = 0.65) with the greatest differences observed in vessels >22 μm diameter (216 ± 121pl/s vs 258 ± 154pl/s, p = 0.001). Wall shear rate (WSR) was significantly lower for the CCHD group (153 ± 27 s^-1 vs 174 ± 22 s^-1, p = 0.04).

CONCLUSIONS

This iPhone and slit-lamp combination assessment of conjunctival vessels found lower axial velocity, wall shear rate and in the largest vessel group, lower blood volume flow in chronically hypoxic patients with congenital heart disease. With further study this assessment method may have utility in the evaluation of patients with chronic hypoxia.

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.

Quantitative analysis of conjunctival microvasculature imaged using optical coherence tomography angiography

Background

The goal was to quantitatively analyze the bulbar conjunctival microvascular density using optical coherence tomography angiography (OCTA) and compare it to the vessel density using functional slit-lamp biomicroscopy (FSLB).

Methods

Temporal bulbar conjunctiva of 20 eyes (10 healthy subjects) was imaged using both OCTA and FSLB. Image processing was performed including equalization, de-noising, thresholding, and skeletonization. The vessel density was measured by fractal analysis (box counting, Dbox) and pixel counting (%).

Results

Vessel density (Dbox) of the bulbar conjunctiva obtained using OCTA was 1.28 ± 0.01 Dbox, which was significantly lower than the result (1.32 ± 0.01 Dbox, P < 0.001) obtained using FSLB. Furthermore, the vessel density (%) obtained using OCTA was 3.31 ± 0.12%, which was also significantly lower than the result (3.69 ± 0.16%, P < 0.001) obtained using FSLB. No significant correlations (r ranged from 0.21 to 0.32, P > 0.05) between both instruments were found in both vessel density methods (Dbox and percentage). However, in each of the devices, vessel density in Dbox was significantly correlated with the vessel density in percentage (r = 1.0 for FSLB and r = 0.98 for OCTA, both P < 0.001).

Conclusion

This study demonstrated that the vessel density of the bulbar conjunctiva obtained using OCTA can be quantified, and the results were not compatible with that obtained using slit-lamp biomicroscopy photography.

Factors Affecting Microvascular Responses in the Bulbar Conjunctiva in Habitual Contact Lens Wearers

Purpose

To investigate the factors affecting microvascular responses in the bulbar conjunctiva of habitual contact lens (HCL) wearers.

Methods

A functional slit-lamp biomicroscope (FSLB) was used to image the temporal bulbar conjunctiva of habitual contact lens (HCL) wearers and non-contact lens (NCL) wearers. The vessel diameters and blood flow velocities (BFVs) were measured. Fractal analysis using Dbox as vessel density and D0 as vessel complexity were used to quantitatively analyze the microvascular network. One eye each of 91 NCL wearers and 75 HCL wearers was imaged.

Results

The BFV of NCL wearers was 0.50 ± 0.14 mm/s, which was negatively correlated with age (r = -0.22, P < 0.05). The BFV, vessel diameter, Dbox, and D0 of HCL wearers was significantly higher than NCL wearers (P < 0.05). In these HCL wearers, BFVs were positively correlated with contact lens (CL) hours of wear per day and CL days of wear per week. BFV, Dbox, and D0 were not related to CL years of wear, CL power, CL base curve, and CL diameter (P > 0.05).

Conclusions

Vascular responses on the bulbar conjunctiva occurred in HCL wearers and appeared to be unrelated to sex or age, CL years of wear, and lens parameters, indicating that wearing a CL itself may be the predominant factor inducing these responses.

Conjunctival microvascular hemodynamics following vaso-occlusive crisis in sickle cell disease

Painful vaso-occlusive crisis (VOC) is the clinical hallmark of sickle cell disease (SCD). Microcirculatory hemodynamic changes following painful VOC may be indicative of future development of VOC events in subjects with SCD. The purpose of the present study was to determine alterations in conjunctival microvascular hemodynamics during non-crisis state in SCD subjects with a history of VOC. Conjunctival microcirculation imaging was performed to measure conjunctival diameter (D) and axial blood velocity (V) in 10 control and 30 SCD subjects. SCD subjects were categorized into two groups based on their history of VOC within a 2-year period before imaging (with or without VOC-H) and also based on whether there was progression in the rate of VOCs during a 2-year period following imaging as compared to before imaging (with or without VOC-P). Conjunctival V was significantly higher in SCD subjects with VOC-H than in both control subjects and SCD subjects without VOC-H (P≤0.03). Conjunctival V was also significantly higher in SCD subjects with VOC-P compared with control subjects and SCD subjects without VOC-P (P≤0.03). Assessment of the conjunctival microcirculation may be useful for understanding hemodynamic changes that lead to VOC events in SCD subjects.

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.

Conjunctival and pulmonary hemodynamic properties in sickle cell disease subjects with and without pulmonary hypertension

Conjunctival microvascular hemodynamic alterations were reported for the first time in sickle cell subjects with and without pulmonary hypertension. Assessment of the conjunctival microcirculation using noninvasive imaging may improve understanding of microvascular hemodynamic alterations that occur due to pulmonary hypertension in sickle cell disease.

Changes in Conjunctival Hemodynamics Predict Albuminuria in Sickle Cell Nephropathy

BACKGROUND

Albuminuria is an early manifestation of deterioration in renal function in subjects with sickle cell disease (SCD). Hyperfiltration may be an early mechanism for kidney damage in SCD. The purpose of the current study was to determine the association between conjunctival hemodynamics and albuminuria in SCD subjects with preserved glomerular filtration rate.

METHODS

Conjunctival microcirculation imaging was performed to measure conjunctival diameter and axial blood velocity (V) in 35 SCD and 10 healthy control subjects. Albuminuria, defined as albumin excretion ratio (AER), was obtained from the medical charts. Based on the 95% CI of conjunctival V in control subjects (0.40-0.60 mm/s), SCD subjects were allocated to 3 groups: V1 <0.40 mm/s (n = 7), V2 of 0.40-0.60 mm/s (n = 18) and V3 ≥0.60 mm/s (n = 10).

RESULTS

Mean log(AER) measurements in the V1, V2 and V3 groups were 1.08 ± 0.67, 1.39 ± 0.59 and 2.00 ± 0.91 mg/g creatinine, respectively, and followed a positive linear trend from the V1 to V3 groups (p = 0.01). By multivariate linear regression analysis, conjunctival V significantly correlated with albuminuria (p = 0.01) independent of age, blood pressure, α-thalassemia, hematocrit, white blood cell count and lactate dehydrogenase concentration.

CONCLUSIONS

Increased conjunctival V is associated with albuminuria in SCD subjects. Assessment of conjunctival microvascular hemodynamics may improve our understanding of the pathophysiology and clinical management of sickle cell nephropathy.