Nailfold videocapillaroscopy in antineutrophil cytoplasmic antibody-associated vasculitis

OBJECTIVE

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of illnesses that cause inflammation and alterations to small vessels in the body. Some of the most common and detrimental manifestations, including alveolar hemorrhage and glomerulonephritis, are caused by this capillary inflammation. We sought to clarify whether patients with AAV would have abnormal nailfold capillaries when evaluated with nailfold videocapillaroscopy.

METHODS

Patients with a current diagnosis of AAV and a control group were identified for enrollment. Nailfold videocapillaroscopy images were used for a semiquantitative analysis on capillary density, morphology, dilation, and microhemorrhage after review by 2 rheumatologists. Disease characteristics, occurrence of recent disease flare, and presence of ANCA were recorded.

RESULTS

Thirty-three patients with a diagnosis of AAV and 21 controls were recruited. The AAV group had a median age of 59 and 17 (52%) were women. Granulomatosis with polyangiitis was the most common diagnosis (19 [58%]), followed by eosinophilic granulomatosis with polyangiitis (7 [21%]) and microscopic polyangiitis (7 [21%]). Twenty-seven patients (82%) had positive ANCA tests. After assessment of capillary density, dilation, morphology, microhemorrhages, and disorganization, there were no statistically significant differences between the 2 groups.

CONCLUSION

There was no evidence of differences in nailfold capillaroscopy abnormalities between those diagnosed with AAV and the control group. While this cohort was relatively small, we did not find a high enough prevalence or specific phenotype of capillary abnormalities that could aid in diagnosis or prognostication of these diseases in the clinical setting.

Peripheral nailfold capillary microscopic abnormalities in rheumatoid arthritis are associated with arterial stiffness: Results from a cross-sectional study

Vascular injury eventually resulting in the establishment of cardiovascular disease is a serious complication in rheumatoid arthritis (RA). Nailfold videocapillaroscopy (NVC) is a non-invasive imaging modality that enables the quantitative and qualitative assessment of the peripheral microvasculature. Nevertheless, capillaroscopic patterns remain inadequately defined in RA, especially regarding their clinical significance as potential markers of systemic vascular impairment. Consecutive RA patients underwent NVC using a standardized protocol, to assess the following parameters: capillary density, avascular areas, capillary dimensions, microhemorrhages, subpapillary venous plexus, and presence of ramified, bushy, crossed and tortuous capillaries. Carotid-femoral pulse wave velocity (PWV) and pulse pressure were measured as well-acknowledged markers of large artery stiffening. The vast majority of our cohort (n = 44) presented a combination of non-specific and abnormal capillaroscopic parameters. Capillary ramification was associated with both PWV and pulse pressure, even after adjustment for cardiovascular risk factors and systemic inflammation. Our study highlights the high prevalence of a wide range of capillaroscopic deviations from the normal patterns in RA. Furthermore, it provides for the first time evidence of an association between structural disorders of the microcirculation and markers of macrovascular dysfunction, suggesting that NVC might have a role as an index of generalised vascular impairment in RA.

Automated nailfold capillary density measurement method based on improved YOLOv5

Nailfold capillary density is an essential physiological parameter for analyzing nailfold health; however, clinical images of the nailfold are taken in many situations, and most clinicians subjectively analyze nailfold images. Therefore, based on the improved "you only look once v5" (YOLOv5) algorithm, this study proposes an automated method for measuring nailfold capillary density. The improved technique can effectively and rapidly detect distal capillaries by incorporating methods or structures such as 9mosaic, spatial pyramid pooling cross-stage partial construction, bilinear interpolation, and efficient intersection over union. First, the modified YOLOv5 algorithm was used to detect nailfold capillaries. Subsequently, the number of distal capillaries was filtered using the 90° method. Finally, the capillary density was calculated. The results showed that the Average Precision (AP)@0.5 value of the proposed approach reached 85.2 %, which was an improvement of 4.93 %, 5.24 %, and 107 % compared with the original YOLOv5, YOLOv6, and simple-faster rapid-region convolutional network (R-CNN), respectively. For different nailfold images, using the density calculated by nailfold experts as a benchmark, the calculated results of the proposed method were consistent with the manually calculated results and superior to those of the original YOLOv5.

Involvement of the systemic microcirculation in pediatric uveitis

BACKGROUND

Pediatric uveitis is a severe inflammatory ocular condition that can lead to sight-threatening complications and can negatively impact quality of life. The retinal microcirculation is often affected in intermediate uveitis and panuveitis. Here, we examined the extraocular (i.e., systemic) microcirculation in pediatric uveitis cases and healthy controls using nailfold capillaroscopy (NFC).

METHODS

We performed NFC in 119 children with noninfectious uveitis and 25 healthy pediatric controls, and assessed the following parameters: capillary density (number of capillaries/mm), dilated capillaries (apex > 20 µm), avascular area, the presence of microhemorrhages, and capillary morphology. Differences in NFC parameters between cases and controls were calculated using regression analysis after adjusting for age and sex.

RESULTS

The mean (± SD) age of the patient group was 13.7 (± 3) years, with 56% females; 46%, 18%, and 36% of cases presented as anterior uveitis, intermediate uveitis, and panuveitis, respectively, with an overall mean disease duration of 4.7 (± 4.0) years. Compared to the control group, the pediatric uveitis cases had a significantly higher number of dilated capillaries/mm and a higher prevalence of ramified capillaries. Moreover, compared to the control group the intermediate uveitis cases had a significantly higher number of dilated capillaries, whereas the anterior uveitis cases had a lower capillary density and a higher prevalence of ramified capillaries.

CONCLUSIONS

Children with uveitis without systemic disease can present with changes in systemic microcirculation. These changes vary amongst the subtypes of uveitis.

Nailfold capillaroscopy: tips and challenges

Although nailfold capillaroscopy (NFC) appears to have a bright future in clinical practice, the lack of familiarity with the technique and how to interpret its outcomes is major barriers which have made nailfold capillaroscopy an underutilized method in standard clinical practice. Traditional methods for assessment and measurement of capillary patterns, density, and blood flow are falling behind and face some challenges. In fact, there have been calls for improvement, hence the recent publication of the standardization of NFC by the EULAR Study Group on Microcirculation in Rheumatic Diseases. Nailfold capillaroscopy has the advantage of being a non-invasive technique that provides a window into the digital microcirculation. This paved the way for a rapidly growing interest in using capillaroscopy parameters as outcome measures in research. In standard clinical practice, whilst its main application is in the identification of an underlying systemic sclerosis spectrum disorder in patients presenting with Raynaud's phenomenon, its use has expanded to include other clinical features possibly suggestive of an underlying connective tissue disease. This article presents the challenges, provides tips, and highlights the exciting potential of nailfold capillaroscopy in standard practice.

Optoacoustic Imaging And Potential Applications Of Raster-Scan Optoacoustic Mesoscopy In Dermatology

Optoacoustic imaging (OAI) is a hybrid imaging modality that integrates the benefits of optical contrast and ultrasound detection. Raster-scan optoacoustic mesoscopy (RSOM) is an emerging OAI method that provides information about several dermatological conditions' structural, functional, and molecular features. We searched PubMed and Google Scholar databases through September 2021 for articles relevant to OAI in the English language. This review contains 32 studies and other relevant literature. Several studies indicate that RSOM is helpful in inflammatory skin conditions such as psoriasis and eczema, especially as it allows more accurate quantification of inflammation-related alterations such as changes to the dermal vasculature. In psoriasis, RSOM can provide objective early diagnosis and monitoring of disease activity and treatment efficacy. Multispectral RSOM, a method in which skin is lightened at more than a single wavelength, is beneficial in diagnosing and monitoring hypoxia-associated conditions, such as systemic sclerosis and chronic wounds. OAI techniques can visualize the pathological vascularization of skin cancers and quantify their oxygenation status which helps differentiate them from normal skin. Also, they can measure the depth of malignant melanoma and detect the metastatic spread of melanoma cells to sentinel lymph nodes. As demonstrated in this article, there is a large spectrum of potential applications of OAI imaging, especially RSOM, in diagnosing, treating, and managing skin diseases.

Nailfold Capillaroscopy as a Biomarker in the Evaluation of Pediatric Inflammatory Bowel Disease

BACKGROUND

Noninvasive screening and disease monitoring are an unmet need in pediatric inflammatory bowel disease (IBD). Nailfold capillaroscopy (NFC) is a validated technique for microvascular surveillance in rheumatologic diseases. NFC uses magnified photography to examine nail bed capillaries called end row loops (ERL). We aimed to identify variations in NFC in pediatric IBD patients and their associations with disease activity.

METHODS

Pediatric patients with Crohn's disease (CD) or ulcerative colitis (UC) and healthy controls were recruited. NFC was performed on patients with newly diagnosed IBD prior to initiating therapy, patients with established IBD, and controls. ERLs were quantified along with a 3mm distance on 8 nailfolds. Serum biomarker levels of disease activity and symptoms activity indexes were correlated with average ERL density digits on both hands. Statistics were performed using chi-squared, ANOVA, and linear regression.

RESULTS

Fifty-one IBD patients and 16 controls were recruited. ERL density was significantly decreased in IBD (Control: 19.2 ERL/3mm vs UC: 15.6 ERL/3mm vs CD: 15.4 ERL/3mm; P < .0001). ERL density was lower in UC patients with lower albumin levels (P = .02, r ² = 0.29).The change in ERL density over time predicted the change in pediatric CD activity index among CD patients (P = .048, r ² = 0.58) with treatment.

CONCLUSIONS

Our data demonstrate ERL density is reduced in IBD compared to controls. Lower albumin levels correlated with lower ERL density in UC. In newly diagnosed CD, ERL density increases over time as disease activity improves with therapy. NFC may be a feasible biomarker of disease activity and utilized for monitoring IBD.

Peripheral microcirculatory abnormalities are associated with cardiovascular risk in systemic sclerosis: a nailfold video capillaroscopy study

INTRODUCTION

Microvascular dysfunction is the key element in the pathogenesis of systemic sclerosis (SSc), whereas the contribution of large and medium size vessel abnormalities is yet to be established. The aim of the present study is to assess the association between micro- and macrovascular function by utilizing a broad spectrum of assessments of vascular performance.

METHODS

We included consecutive, consenting SSc patients who underwent nailfold video capillaroscopy (NVC) for microcirculation evaluation. Peripheral and central systolic and diastolic blood pressure, carotid intima-media thickness (cIMT), aortic augmentation index (AIx) corrected for a heart rate of 75 beats per minute (AIx-75), and carotid-femoral pulse wave velocity (PWV) were also performed to assess macrovascular function. Cardiovascular risk disease (CVD) algorithms were also calculated and included in the analysis.

RESULTS

A total of 81 patients (6 males) were studied with mean age 55.44 ± 13.40 years. Reduced capillary density was inversely correlated with arterial stiffness (Alx-75) and augmentation pressure (r =  - 0.262, p = 0.018, and r =  - 0.249, p = 0.025 respectively). Alx was significantly lower in the early compared to late pattern (28.24 ± 11.75 vs 35.63 ± 10.47, p = 0.036). A significant trend was found among NVC patterns with Alx-75 values being higher with the progression of microangiopathy towards the "late" group (26.36 ± 10.90 vs 30.81 ± 11.59 vs 35.21 ± 7.90, p = 0.027 for trend). Similarly, Framingham risk score and Atherosclerotic Cardiovascular Disease score were progressively higher across the worsening NVC patterns (4.10 ± 4.13 vs 2.99 ± 2.72 vs 6.36 ± 5.65, p = 0.023, and 6.99 ± 7.18 vs 5.63 ± 4.41 vs 12.09 ± 9.90, p = 0.019, respectively, for trends). Finally, QRISK3 (10-year cardiovascular disease risk) and ASCVD (Atherosclerotic Cardiovascular Disease) scores were inversely correlated with the number of capillaries (r =  - 0.231, p = 0.048, and r =  - 0.260, p = 0.038 respectively).

CONCLUSION

These data suggest that CVD risk scores and macrovascular parameters are strongly correlated with microvasculopathy in patients with SSc. Key Points • Microangiopathy is the hallmark of SSc, but the relationship between subclinical atherosclerosis and small vessel disease remains unknown. • Arterial stiffening and CVD risk scores are positively associated with the degree of progression of peripheral microvasculopathy assessed with NVC. • The results of the study suggest an association between NVC abnormalities and higher CVD risk in SSc patients.

Paired Optic Nerve Microvasculature and Nailfold Capillary Measurements in Primary Open-Angle Glaucoma

Purpose

To assess microvascular beds in the optic nerve head (ONH), peripapillary tissue, and the nailfold in patients with primary open-angle glaucoma (POAG) versus controls.

Methods

Patients with POAG (n = 22) and controls (n = 12) underwent swept-source optical coherence tomography angiography of ophthalmic microvasculature and nailfold video capillaroscopy of the hand. The main outcomes were vessel density (VD) and blood flow of the ONH, the peripapillary and the nailfold microvasculatures.

Results

Patients with POAG were younger than controls (63.5 ± 9.4 vs. 69.9 ± 6.5 years, P = 0.03). Deep ONH VD and blood flow were lower in patients with POAG than controls (39.1% ± 3.5% vs. 43.8% ± 5.7%; 37.8% ± 5.3% vs. 46.0% ± 7.8%, respectively, P < 0.02 for both); similar results were observed with peripapillary VD (37.9 ± 2.6%, 43.4 ± 7.6%, respectively, P = 0.03). Nailfold capillary density and blood flow were lower in patients with POAG than controls (8.8 ± 1.0 vs. 9.8 ± 0.9 capillaries/mm; 19.9 ± 9.4 vs. 33.7 ± 9.8 pL/s, respectively; P < 0.009 for both). After adjusting for age and gender, deep ONH VD and blood flow, peripapillary VD, and nailfold capillary blood flow were lower in POAG than controls (β = −0.04, −0.07, −0.05, −13.19, respectively, P ≤ 0.046 for all). Among all participants, there were positive correlations between deep ONH and nailfold capillary blood flow (Pearson's correlation coefficient r = 0.42, P = 0.02), peripapillary and nailfold capillary density (r = 0.43, P = 0.03), and peripapillary and nailfold capillary blood flow (r = 0.49, P = 0.01).

Conclusions

Patients with POAG demonstrated morphologic and hemodynamic alterations in both ophthalmic and nailfold microvascular beds compared to controls.

Translational Relevance

The concomitant abnormalities in nailfold capillaries and relevant ocular vascular beds in POAG suggest that the microvasculature may be a target for POAG treatment.

Quantitative nailfold capillaroscopy-update and possible next steps

We review the exciting potential (and challenges) of quantitative nailfold capillaroscopy, focusing on its role in systemic sclerosis. Quantifying abnormality, including automated analysis of nailfold images, overcomes the subjectivity of qualitative/descriptive image interpretation. First we consider the rationale for quantitative analysis, including the potential for precise discrimination between normal and abnormal capillaries and for reliable measurement of disease progression and treatment response. We discuss nailfold image acquisition and interpretation, and describe how early work on semi-quantitative and quantitative analysis paved the way for semi-automated and automated analysis. Measurement of red blood cell velocity is described briefly. Finally we give a personal view on 'next steps'. From a clinical perspective, increased uptake of nailfold capillaroscopy by general rheumatologists could be achieved via low-cost hand-held devices with cloud-based automated analysis. From a research perspective, automated analysis could facilitate large-scale prospective studies using capillaroscopic parameters as possible biomarkers of systemic sclerosis-spectrum disorders.

Nailfold videocapillaroscopic changes in patients with pulmonary arterial hypertension associated with connective tissue diseases

Pulmonary arterial hypertension (PAH) represents one of the most devastating complications in connective tissue diseases (CTDs). The aim of this study was to investigate the presence of peripheral microangiopathy in patients with PAH associated with CTDs (CTD-PAH) by exploring nailfold videocapillaroscopic (NVC) changes and identify possible associations of NVC characteristics with markers of disease severity. Α cross-sectional study was performed in 18 CTD-PAH patients [13 PAH due to systemic sclerosis (SSc-PAH) and 5 with other types of CTD-PAH], 14 patients with SSc without PAH (SSc-non-PAH) and 20 healthy controls. NVC quantitative and qualitative parameters were evaluated using Optilia Digital Capillaroscope. To ensure inter-observer repeatability, capillaroscopic images were reviewed by two independent investigators. When compared to healthy controls, patients with CTD-PAH (77.8% women, mean age 65.9 years) presented reduced capillary density (6.5 ± 1.6 loops/mm vs. 9.7 ± 0.7 loops/mm, p < 0.001) and increased capillary loop width (23.3 ± 10.1 μm vs. 11.2 ± 2.5 μm, p < 0.001). SSc-PAH patients presented lower capillary density in comparison with other CTD-PAH patients and SSc-non-PAH subjects and abnormal and disorganized capillaries compared to controls. Patients with other CTD-PAH had also reduced capillary density and increased loop diameter compared to controls. A significant linear correlation was identified between capillary density and estimated glomerular filtration rate in the total CTD-PAH population (r = 0.63, p = 0.007). In SSc-PAH group, capillary loop diameter was positively correlated to cardiac index (r = 0.61, p = 0.02). Significant NVC microvascular changes were detected in patients with various types of CTD-PAH, suggesting an impaired peripheral microcirculation parallel to pulmonary vasculopathy.

Peripheral microangiopathy in Eisenmenger syndrome: A nailfold video capillaroscopy study

BACKGROUND

Eisenmenger syndrome (ES) comprises a severe phenotype of pulmonary arterial hypertension characterized by angiopathy of the lung circulation. The aim of the present study was to demonstrate the presence of systemic microvascular abnormalities in patients with ES using nailfold video-capillaroscopy (NVC) and to identify potential correlations of nailfold capillaroscopic characteristics with non-invasive markers of systemic organ function.

METHODS

Α cross-sectional NVC study was performed in 17 consecutive patients with ES and 17 healthy controls matched for age and sex. NVC quantitative (capillary density, capillary dimensions, haemorrhages, thrombi, shape abnormalities) and qualitative (normal, non-specific or scleroderma pattern) parameters were evaluated.

RESULTS

Patients with ES [median age 40 (18-65) years, 11 women] presented reduced capillary density [8.8 (7.2-10.2) loops/mm vs. 9.9 (8.3-10.9) loops/mm, p = .004] and increased loop width [15.9 (10.3-21.7) μm vs. 12.3 (7.6-15.2) μm, p < .001], while they had significantly more abnormal capillaries than healthy controls [2.5 (0.9-5.4) abnormal loops/mm vs. 1.0 (0.0-1.7) abnormal loops/mm, p < .001]. NVC shape abnormalities in ES were positively correlated with NT-proBNP (r = 0.52, p = .03) and were negatively associated with estimated glomerular filtration rate (r = -0.60, p = .02). Additionally, capillary loop diameter was positively correlated with increased haemoglobin levels (r = 0.55, p = .03) and negatively correlated with reduced peripheral oxygen saturation (r = - 0.56, p = .02).

CONCLUSIONS

This study supports the hypothesis of peripheral microvascular involvement in ES parallel to pulmonary microangiopathy detected by NVC. Further longitudinal studies are needed to confirm our preliminary results.

Prevalence of retinal changes in patients with systemic sclerosis: the association between retinal vascular changes and nailfold capillaroscopic findings

Background

Systemic sclerosis (SSc) is a connective tissue disease affecting the skin and multiple organs. Most of the evidence on ocular involvement comes from small studies. We evaluated the retinal vascular changes in patients with SSc and its associations with types, disease duration, skin score, and nailfold capillaroscopy changes.

Material and methods

We evaluated the demographic, clinical and nailfold capillaroscopy data of 52 patients referring to the clinic of scleroderma with SSc according to the 2013 ACR/EULAR SSc criteria. In addition, full ophthalmic examination in 52 patients and fundus photography in 40 patients were done in the ophthalmology clinic.

Results

There were 52 (49 women and 3 men, 17 diffuse and 35 limited) patients with SSc with mean disease duration of 8 ±5 years and mean age of 40 ±9 years. Retinal changes in the ophthalmologic examination were seen in 30.7% as increased vascular tortuosity. None of the patients had cotton wool spot, hemorrhage or hard exudate. Forty patients underwent fundus photography and 22.5% of them had vascular tortuosity. Only the presence of hemorrhage in the nailfolds was correlated with retinal tortuosity, and the other characteristics of nailfold capillaroscopy did not have any association with retinal changes.

Conclusions

Retinal vascular changes were seen in about one third of our patients. There was no correlation between nailfold capillaroscopy, disease duration, type and skin score of SSc patients and retinal vascular changes. These findings suggest that the mechanisms or the quality of changes in the retinal vessels and nailfold vasculature may be different.

Peripheral microangiopathy in precapillary pulmonary hypertension: a nailfold video capillaroscopy prospective study

Background

Although pulmonary vascular bed has been the main subject of research for many years in pulmonary hypertension (PH), interest has recently started to divert towards the possibility of a co-existing peripheral microangiopathy. The aim of the current study was to investigate the presence of nailfold video-capillaroscopic (NVC) structural changes in patients with precapillary PH and to identify possible associations of NVC measurements with markers of disease severity.

Methods

Α prospective case–control study was performed in 28 consecutive patients with precapillary PH [14 with idiopathic pulmonary arterial hypertension (IPAH) and 14 with chronic thromboembolic pulmonary hypertension (CTEPH)] and 30 healthy controls. NVC quantitative and qualitative parameters were evaluated using Optilia Digital Capillaroscope. To ensure inter-observer repeatability capillaroscopic images were reviewed by two independent investigators. For multiple comparisons among continuous variables, one-way ANOVA or the Kruskal–Wallis test were used. Differences between the groups were tested with post-hoc analysis with adjustment for multiple comparisons (Bonferroni test).

Results

Both IPAH (71.4% were women, mean age 53.1 ± 13.4 years) and CTEPH (64.3% women, mean age 60.9 ± 14.4 years) groups presented reduced capillary density compared to healthy controls (8.4 ± 1.2 loops/mm and 8.0 ± 1.2 loops/mm vs. 9.7 ± 0.81 loops/mm, p < 0.001) and increased loop width (15.7 ± 3.9 μm and 15.8 ± 1.9 μm vs. 11.5 ± 2.3 μm, p < 0.001). More than half of patients with IPAH presented microhaemorrhages on capillary nailfold, while increased shape abnormalities in capillary morphology and more capillary thrombi per linear mm were detected in patients with CTEPH compared to patients with IPAH and healthy controls. All PH patients presented a non-specific NVC pattern compared to controls (p < 0.001).

Conclusion

The findings of the study reveal a degree of significant peripheral microvascular alterations in patients with IPAH and CTEPH, suggesting a generalized impairment of peripheral microvasculature in pulmonary vascular disease.

Fast track algorithm: How to differentiate a "scleroderma pattern" from a "non-scleroderma pattern"

OBJECTIVES

This study was designed to propose a simple "Fast Track algorithm" for capillaroscopists of any level of experience to differentiate "scleroderma patterns" from "non-scleroderma patterns" on capillaroscopy and to assess its inter-rater reliability.

METHODS

Based on existing definitions to categorise capillaroscopic images as "scleroderma patterns" and taking into account the real life variability of capillaroscopic images described standardly according to the European League Against Rheumatism (EULAR) Study Group on Microcirculation in Rheumatic Diseases, a fast track decision tree, the "Fast Track algorithm" was created by the principal expert (VS) to facilitate swift categorisation of an image as "non-scleroderma pattern (category 1)" or "scleroderma pattern (category 2)". Mean inter-rater reliability between all raters (experts/attendees) of the 8th EULAR course on capillaroscopy in Rheumatic Diseases (Genoa, 2018) and, as external validation, of the 8th European Scleroderma Trials and Research group (EUSTAR) course on systemic sclerosis (SSc) (Nijmegen, 2019) versus the principal expert, as well as reliability between the rater pairs themselves was assessed by mean Cohen's and Light's kappa coefficients.

RESULTS

Mean Cohen's kappa was 1/0.96 (95% CI 0.95-0.98) for the 6 experts/135 attendees of the 8th EULAR capillaroscopy course and 1/0.94 (95% CI 0.92-0.96) for the 3 experts/85 attendees of the 8th EUSTAR SSc course. Light's kappa was 1/0.92 at the 8th EULAR capillaroscopy course, and 1/0.87 at the 8th EUSTAR SSc course.

CONCLUSION

For the first time, a clinical expert based fast track decision algorithm has been developed to differentiate a "non-scleroderma" from a "scleroderma pattern" on capillaroscopic images, demonstrating excellent reliability when applied by capillaroscopists with varying levels of expertise versus the principal expert and corroborated with external validation.

Practical issues in assessing nailfold capillaroscopic images: a summary

Nailfold capillaroscopy (NC) is a highly sensitive, safe, and non-invasive technique to assess involvement rate of microvascularity in dermatomyositis and systemic sclerosis. A large number of studies have focused on NC pattern description, classification, and scoring system validation, but minimal information has been published on the accuracy and precision of the measurement. The objective of this review article is to identify different factors affecting the reliability and validity of the assessment in NC. Several factors can affect the reliability of the examination, e.g., physiological artifacts, the nailfold imaging instrument, human factors, and the assessment rules and standards. It is impossible to avoid all artifacts, e.g., skin transparency, physically injured fingers, and skin pigmentation. However, minimization of the impact of some of these artifacts by considering some protocols before the examination and by using specialized tools, training, guidelines, and software can help to reduce errors in the measurement and assessment of NC images. Establishing guidelines and instructions for automatic characterization and measurement based on machine learning techniques also may reduce ambiguities and the assessment time.

Non-invasive imaging in dermatology and the unique potential of raster-scan optoacoustic mesoscopy

In recent years, several non‐invasive imaging methods have been introduced to facilitate diagnostics and therapy monitoring in dermatology. The microscopic imaging methods are restricted in their penetration depth, while the mesoscopic methods probe deeper but provide only morphological, not functional, information. ‘Raster‐scan optoacoustic mesoscopy’ (RSOM), an emerging new imaging technique, combines deep penetration with contrast based on light absorption, which provides morphological, molecular and functional information. Here, we compare the capabilities and limitations of currently available dermatological imaging methods and highlight the principles and unique abilities of RSOM. We illustrate the clinical potential of RSOM, in particular for non‐invasive diagnosis and monitoring of inflammatory and oncological skin diseases.

Automated assessment of absolute nailfold capillary number on videocapillaroscopic images: Proof of principle and validation in systemic sclerosis

BACKGROUND

Absolute nailfold capillary number should be a putative biomarker in selected rheumatic diseases but could be time-consuming and not highly repeatable.

OBJECTIVE

To validate an automated software for absolute nailfold capillary number and density evaluation, on NVC images in SSc.

METHODS

An automated software to count nailfold capillary number (AUTOCAPI) had been constructed, through an exploratory image set. Subsequently, application rules have been created to define the ROI in NVC images, through a training images set. The software reliability was assessed through calculation of the ICC between automatic and manual counting, by four independent observers, on the same NVC images.

RESULTS

The following ICC's were obtained per observer, for the patients with SSc (40 images), the healthy (20 images), and the PRP subgroups (20 images), respectively: 0.94, 0.81, and 0.62 (observer 1); 0.94, 0.91, and 0.67 (observer 2); 0.88, 0.56, and 0.64 (observer 3); and 0.88, 0.85, and 0.85 (observer 4).

CONCLUSIONS

The validation of an automated software for measuring absolute nailfold capillary number and density in SSc was achieved. The integration into the pre-existing imaging software should make the assessment of the capillary number in NVC easier, quicker, and standardized.

Quantitative videocapillaroscopy correlates with functional respiratory parameters: a clue for vasculopathy as a pathogenic mechanism for lung injury in systemic sclerosis

Background

To determine whether lung involvement is related to microvascular perturbations, nailfold videocapillaroscopy (NVC) was performed in patients with systemic sclerosis (SSc).

Methods

A cross-sectional study was consecutively accomplished in 152 SSc patients. NVC, a pulmonary function test and echocardiography were undergone within a 3-month period. Finally, 134 patients with at least eight NVC (200× magnification) images were selected for quantitative and qualitative examinations.

Results

Patients with interstitial lung disease presented lower median capillary density (4.86/mm vs 5.88/mm, p = 0.005) and higher median of neoangiogenesis (0.56/mm vs 0.31/mm, p = 0.005). A higher quantity of neoangiogenesis capillaries was found in patients with pulmonary arterial hypertension (0.70/mm vs 0.33/mm, p = 0.008). Multivariate linear regression analysis established a correlation between neoangiogenesis and decreased forced vital capacity (FVC) (p < 0.001): for each capillary with neoangiogenesis visualized on average per 1 mm, FVC was 7.3% reduced. In qualitative NVC, a late pattern as defined by Cutolo was also associated with lower FVC (p = 0.018). The number of giant capillaries was associated with reduced diffusion capacity of the lung for carbon monoxide (DLCO) (p = 0.016); for each giant capillary per 1 mm, DLCO was 11.8% diminished.

Conclusions

A good correlation was observed between distinctive quantitative and qualitative NVC features with lung functional parameters such as FVC and DLCO. It is suggested that vasculopathy could play a role in SSc lung involvement.

Image enhancement effect on inter and intra-observer reliability of nailfold capillary assessment

BACKGROUND

Nailfold capillaroscopy (NC) is a diagnostic imaging technique that is used to assess the blood capillary network in the nailfold area. NC is routinely used for patients with microcirculation problems, such as systemic sclerosis and other connective tissue diseases. Experts commonly use subjective evaluation as a reference point in images of nailfold video capillaroscopy, so it is important to reduce the inherent ambiguities in human judgment and diagnosis. Image quality is an important factor that affects measurement error and assessment time of NC images.

OBJECTIVE

In this study, a new image enhancement technique was introduced and evaluated subjectively.

METHODS

In total, 475 nailfold video capillaroscopy images from 18 healthy subjects and 41 systemic lupus erythematosus patients were used. The images were randomly divided into two sets, one each with 275 and 200. Eight independent observers who were familiar with the capillaroscopy technique participated in this study. The set of 275 images was evaluated by three observers with the forced-choice pairwise comparison method. Elliptic broken line (EBL) was used to count the number of capillaries. The intra- and inter-observer reliability of the original and enhanced images was evaluated on 200 images by five observers.

RESULT

Except for eight images, all observers preferred the enhanced images in the visual quality comparison method. The intra-class correlation coefficient (ICC) of intra- and inter-observer reliability increased from 0.76-0.84 to 0.82-0.89, respectively, when using the enhancement method.

CONCLUSION

By improving the image quality, more capillary details will be visible, and an observer can document more details that may not be visible in the original image and can do so more efficiently.

Assessing nailfold microvascular structure with ultra-wideband raster-scan optoacoustic mesoscopy

Nailfold capillaroscopy, based on bright-field microscopy, is widely used to diagnose systemic sclerosis (SSc). However it cannot reveal information about venules and arterioles lying deep under the nailfold, nor can it provide detailed data about surface microvasculature when the skin around the nail is thick. These limitations reflect the fact that capillaroscopy is based on microscopy methods whose penetration depth is restricted to about 200 μm. We investigated whether ultra-wideband raster-scan optoacoustic mesoscopy (UWB-RSOM) can resolve small capillaries of the nailfold in healthy volunteers and compared the optoacoustic data to conventional capillaroscopy examinations. We quantified UWB-RSOM-resolved capillary density and capillary diameter as features that relate to SSc biomarkers, and we obtained the first three-dimensional, in vivo images of the deeper arterioles and venules. These results establish the potential of UWB-RSOM for analyzing SSc-relevant markers.

Non-invasive detection of severe neutropenia in chemotherapy patients by optical imaging of nailfold microcirculation

White-blood-cell (WBC) assessment is employed for innumerable clinical procedures as one indicator of immune status. Currently, WBC determinations are obtained by clinical laboratory analysis of whole blood samples. Both the extraction of blood and its analysis limit the accessibility and frequency of the measurement. In this study, we demonstrate the feasibility of a non-invasive device to perform point-of-care WBC analysis without the need for blood draws, focusing on a chemotherapy setting where patients’ neutrophils—the most common type of WBC—become very low. In particular, we built a portable optical prototype, and used it to collect 22 microcirculatory-video datasets from 11 chemotherapy patients. Based on these videos, we identified moving optical absorption gaps in the flow of red cells, using them as proxies to WBC movement through nailfold capillaries. We then showed that counting these gaps allows discriminating cases of severe neutropenia (<500 neutrophils per µL), associated with increased risks of life-threatening infections, from non-neutropenic cases (>1,500 neutrophils per µL). This result suggests that the integration of optical imaging, consumer electronics, and data analysis can make non-invasive screening for severe neutropenia accessible to patients. More generally, this work provides a first step towards a long-term objective of non-invasive WBC counting.

The emerging application of semi-quantitative and quantitative capillaroscopy in systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disease with high morbidity and mortality, characterized by autoimmunity, obliterative vasculopathy involving mainly the microvasculature, and fibrosis. SSc-specific nailfold capillaroscopic changes have been defined, and nailfold capillaroscopy (NFC) is now unequivocally accepted to be a cornerstone for the early diagnosis of SSc. However, the use of NFC in patients already diagnosed with SSc is still not standardized. Several studies have shown that NFC abnormalities correlate with disease activity and severity and are predictive for disease worsening, such as occurrence of new digital ulcers. More importantly, successful treatment has been shown to diminish NFC abnormalities in severe SSc cases. These findings support the importance of NFC in monitoring patients with SSc and even its role as an outcome measure in SSc clinical trials. It is a matter of debate if Semi-quantitative and Quantitative NFC would be a more sensitive tool than qualitative NFC for meeting these objectives. This review is presenting the emerging application of Semi-quantitative and Quantitative NFC in SSc and its potential benefits.

Can nailfold videocapillaroscopy images be interpreted reliably by different observers? Results of an inter-reader and intra-reader exercise among rheumatologists with different experience in this field

Nailfold videocapillaroscopy (VCP) allows non-invasive assessment of the microcirculation. Adequate training in this field is relevant for rheumatologists. There is increasing evidence of the reliability of VCP findings among different readers. Objective: To evaluate inter- and intra-reader agreement of rheumatologists to identify normal images and systemic sclerosis (SSc) patterns on VCP ("early," "active," and "late" proposed by Cutolo et al.). Thirteen rheumatologists with different experience in nailfold VCP received training to standardize reading criteria. They rated 60 VCP images from healthy and SSc patients at baseline and 4 weeks later, using an electronic platform. The reading of an expert was considered the gold standard. Data were analyzed using Cohen's kappa for concordance and Student's t test and ANOVA to compare kappa means for inter-reader, intra-reader, and inter-pattern readings. Mean inter-reader and intra-reader kappa were 0.45 and 0.49, respectively, (moderate agreement). Kappa scores were higher among experienced vs inexperienced readers (inter-reader kappa 0.58 vs 0.34, p = 0.001, intra-reader kappa 0.65 vs 0.37, p = 0.01). Agreement was substantial (kappa = 0.61) for the identification of normal vs abnormal images and higher for the identification of active (0.48, p = 0.009) and late SSc patterns (0.56, p = 0.008) than for the early SSc pattern (0.35, p = 0.003). There is moderate agreement among rheumatologists for the identification of SSc videocapillaroscopy patterns (higher among experienced rheumatologists) and substantial agreement, regardless of previous experience in VCP, in the identification of normal and abnormal images. Agreement for the identification of active and late patterns is higher than for the early pattern.

Reproducibility of capillaroscopic classifications of systemic sclerosis: results from the SCLEROCAP study

Objectives

Subgroups of capillaroscopic scleroderma landscape have been correlated with stages of SSc: two groups for Maricq's classification (slow and active), and three for Cutolo's classification (early, active and late). We report inter- and intra-observer agreement for these classifications as a preliminary step in the multicentre prospective SCLEROCAP study, which aims to assess the classification and single capillaroscopic items as prognostic tools for SSc.

Methods

SCLEROCAP included 385 patients. Agreement was studied in the first 100 patients, who were independently rated twice by two observers, blind to patients' characteristics; 30 of the patients were rated once by six observers. After consensus meetings, these ratings were held again. Kappa and intraclass correlation coefficients were used to assess agreement.

Results

Interobserver agreement on 100 patients was moderate for Maricq and Cutolo classifications [κ 0.47 (0.28, 0.66) and 0.49 (0.33, 0.65), respectively], and became substantial after consensus meetings [0.64 (0.50, 0.77) and 0.69 (0.56, 0.81)]. Intra-observer agreement between two observers was moderate to substantial: κ 0.54 (0.33, 0.75) and 0.70 (0.57, 0.83) for Maricq's classification; 0.57 (0.38, 0.77) and 0.76 (0.65, 0.87) for Cutolo's. Thirty patients were rated once by each of six observers, and agreement was moderate to substantial: κ 0.57 ± 0.10 (Maricq) and 0.61 ± 0.12 (Cutolo). Agreement was substantial for bushy, giant capillaries and microhaemorrhages, moderate for capillary density and low for oedema, disorganization and avascular areas.

Conclusion

The moderate reproducibility of Maricq and Cutolo classifications might hamper their prognostic value in SSc patients. Consensus meetings improve reliability, a prerequisite for better prognostic performances. A focus on giant capillaries, haemorrhages and capillary density might be more reliable.

Quantitative outcome measures for systemic sclerosis-related Microangiopathy - Reliability of image acquisition in Nailfold Capillaroscopy

BACKGROUND

Nailfold capillaroscopic parameters hold increasing promise as outcome measures for clinical trials in systemic sclerosis (SSc). Their inclusion as outcomes would often naturally require capillaroscopy images to be captured at several time points during any one study. Our objective was to assess repeatability of image acquisition (which has been little studied), as well as of measurement.

METHOD

41 patients (26 with SSc, 15 with primary Raynaud's phenomenon) and 10 healthy controls returned for repeat high-magnification (300×) videocapillaroscopy mosaic imaging of 10 digits one week after initial imaging (as part of a larger study of reliability). Images were assessed in a random order by an expert blinded observer and 4 outcome measures extracted: (1) overall image grade and then (where possible) distal vessel locations were marked, allowing (2) vessel density (across the whole nailfold) to be calculated (3) apex width measurement and (4) giant vessel count. Intra-rater, intra-visit and intra-rater inter-visit (baseline vs. 1week) reliability were examined in 475 and 392 images respectively. A linear, mixed-effects model was used to estimate variance components, from which intra-class correlation coefficients (ICCs) were determined.

RESULTS

Intra-visit and inter-visit reliability estimates (ICCs) were (respectively): overall image grade, 0.97 and 0.90; vessel density, 0.92 and 0.65; mean vessel width, 0.91 and 0.79; presence of giant capillary, 0.68 and 0.56. These estimates were conditional on each parameter being measurable.

CONCLUSION

Within-operator image analysis and acquisition are reproducible. Quantitative nailfold capillaroscopy, at least with a single observer, provides reliable outcome measures for clinical studies including randomised controlled trials.

Elliptical broken line method for calculating capillary density in nailfold capillaroscopy: Proposal and evaluation

Nailfold capillaroscopy is a practical method for identifying and obtaining morphological changes in capillaries which might reveal relevant information about diseases and health. Capillaroscopy is harmless, and seems simple and repeatable. However, there is lack of established guidelines and instructions for acquisition as well as the interpretation of the obtained images; which might lead to various ambiguities. In addition, assessment and interpretation of the acquired images are very subjective. In an attempt to overcome some of these problems, in this study a new modified technique for assessment of nailfold capillary density is introduced. The new method is named elliptic broken line (EBL) which is an extension of the two previously known methods by defining clear criteria for finding the apex of capillaries in different scenarios by using a fitted elliptic. A graphical user interface (GUI) is developed for pre-processing, manual assessment of capillary apexes and automatic correction of selected apexes based on 90° rule. Intra- and inter-observer reliability of EBL and corrected EBL is evaluated in this study. Four independent observers familiar with capillaroscopy performed the assessment for 200 nailfold videocapillaroscopy images, form healthy subject and systemic lupus erythematosus patients, in two different sessions. The results show elevation from moderate (ICC=0.691) and good (ICC=0.753) agreements to good (ICC=0.750) and good (ICC=0.801) for intra- and inter-observer reliability after automatic correction of EBL. This clearly shows the potential of this method to improve the reliability and repeatability of assessment which motivates us for further development of automatic tool for EBL method.

Intra-and inter-observer reliability of nailfold videocapillaroscopy - A possible outcome measure for systemic sclerosis-related microangiopathy

OBJECTIVES

Our aim was to assess the reliability of nailfold capillary assessment in terms of image evaluability, image severity grade ('normal', 'early', 'active', 'late'), capillary density, capillary (apex) width, and presence of giant capillaries, and also to gain further insight into differences in these parameters between patients with systemic sclerosis (SSc), patients with primary Raynaud's phenomenon (PRP) and healthy control subjects.

METHODS

Videocapillaroscopy images (magnification 300×) were acquired from all 10 digits from 173 participants: 101 patients with SSc, 22 with PRP and 50 healthy controls. Ten capillaroscopy experts from 7 European centres evaluated the images. Custom image mark-up software allowed extraction of the following outcome measures: overall grade ('normal', 'early', 'active', 'late', 'non-specific', or 'ungradeable'), capillary density (vessels/mm), mean vessel apical width, and presence of giant capillaries.

RESULTS

Observers analysed a median of 129 images each. Evaluability (i.e. the availability of measures) varied across outcome measures (e.g. 73.0% for density and 46.2% for overall grade in patients with SSc). Intra-observer reliability for evaluability was consistently higher than inter- (e.g. for density, intra-class correlation coefficient [ICC] was 0.71 within and 0.14 between observers). Conditional on evaluability, both intra- and inter-observer reliability were high for grade (ICC 0.93 and 0.78 respectively), density (0.91 and 0.64) and width (0.91 and 0.85).

CONCLUSIONS

Evaluability is one of the major challenges in assessing nailfold capillaries. However, when images are evaluable, the high intra- and inter-reliabilities suggest that overall image grade, capillary density and apex width have potential as outcome measures in longitudinal studies.

Analysis of white blood cell dynamics in nailfold capillaries

Based on video data acquired with low-cost, portable microscopy equipment, we introduce a semi-automatic method to count visual gaps in the blood flow as a proxy for white blood cells (WBC) passing through nailfold capillaries. Following minimal user interaction and a pre-processing stage, our method consists in the spatio-temporal segmentation and analysis of capillary profiles. Besides the mere count information, it also estimates the speed associated with every WBC event. The accuracy of our algorithm is validated through the analysis of two capillaries acquired from one healthy subject. Results are compared with manual counts from four human raters and confronted with related physiological data reported in literature.

Capillary density: An important parameter in nailfold capillaroscopy

Nailfold capillaroscopy is one of the various noninvasive bioengineering methods used to investigate skin microcirculation. It is an effective examination for assessing microvascular changes in the peripheral circulation; hence it has a significant role for the diagnosis of Systemic sclerosis with the classic changes of giant capillaries as well as the decline in capillary density with capillary dropout. The decline in capillary density is one of microangiopathic features existing in connective tissue disease. It is detectable with nailfold capillaroscopy. This parameter is assessed by applying quantitative measurement. In this article, we reviewed a common method for calculating the capillary density and the relation between the number of capillaries as well as the existence of digital ulcers, pulmonary arterial hypertension, autoantibodies, scleroderma patterns and different scoring system.

Effects of chronic low-dose exposure to ionizing radiation on physician microvascular structure revealed by nail fold capillaroscopy

The aim of this study was to assess the long-term asymptomatic effects of low-dose radiation on microvascular structure among interventional physicians, whose hands are exposed to ionizing radiation during daily practice. The study, approved by the national ethics committee, included 186 radiation-exposed (surgeons, cardiologists, radiologists) and 35 unexposed physicians, all of whom had provided written consent. The subjects completed a questionnaire describing their current and past daily practice, from which tentative estimates of current and cumulative radiation exposure estimates were computed. Subject dermal microcirculation state was assessed by capillaroscopy of the nail fold of eight fingers (thumbs excluded) based on photographs. Two quantitative scores characterizing extravasation and morphological abnormalities based on seven semiquantitative indices were obtained from post hoc coding of the photographs by five capillaroscopists. These evaluations were randomized and blind to the exposure. The effect of the radiation exposure on both abnormality scores was modelled using multilevel proportional odds regression adjusted for potential confounders. The proportion of physicians for which the most frequent act is close to the radiation source was highest among surgeons, but with fewer weekly acts. The median duration of exposure was highest among radiologists and cardiologists. No exposure effect could be detected on the extravasation score. The morphological anomaly score increased significantly with duration of exposure and estimated cumulative exposure among surgeons and interventional radiologists, unlike cardiologists among whom no effect could be detected. It is concluded that the shown effects of chronic low-dose exposure to ionizing radiation on physician microvascular structure reveal the importance of increased exposure monitoring and prevention.

Nailfold Capillaroscopy in Rheumatic Diseases: Which Parameters Should Be Evaluated?

Video nailfold capillaroscopy (NFC), considered as an extension of the widefield technique, allows a more accurate measuring and storing of capillary data and a better defining, analyzing, and quantifying of capillary abnormalities. Capillaroscopic study is often performed on the patients suspected of having microcirculation problems such as Raynaud's phenomenon as the main indication for nailfold capillaroscopy. Capillaroscopic findings based on microcirculation studies can provide useful information in the fields of pathophysiology, differential diagnosis, and monitoring therapy. Nailfold capillaroscopy provides a vital assessment in clinical practices and research; for example, its reputation in the early diagnosis of systemic sclerosis is well established and it is also used as a classification criterion in this regard. This review focuses on the manner of performing video nailfold capillaroscopy and on a common approach for measuring capillary dimensions in fingers and toes.

Precocious markers of cardiovascular risk and vascular damage in apparently healthy women with previous gestational diabetes

Previous gestational diabetes mellitus (pGDM) indicates future risk for type 2 diabetes (T2DM). Insulin resistance (IR) may precede T2DM in many years and is associated with an increased risk for cardiovascular diseases.

AIM

This study aims to identify endothelial dysfunction and cardiovascular risk factors in women with pGDM.

METHODS

This cross-sectional analysis included 45 non diabetic women, 20 pGDM and 25 controls, at least one year after delivery. Body mass index (BMI), abdominal circumference (AC), blood pressure, serum lipids, liver enzymes, uric acid, nonesterified fatty acids, C-reactive protein and plasma glucose, insulin, fibrinogen and plasminogen activator inhibitor 1 were measured. HOMA IR and β were calculated. Pre and post induced ischemia videocapillaroscopy was performed in hand nailfold to evaluate microvascular morphologic aspect and functional response.

RESULTS

AC and fasting glucose were significantly higher in pGDM (p = 0.01 and p = 0.002 respectively). Women with pGDM and BMI < 25 kg/m(2) had significantly higher levels of fasting insulin and HOMA IR than controls (p = 0.008 and 0.05 respectively). Abnormal morphologic findings were more frequent and papillae rectification were 3.3 times more prevalent in pGDM (p = 0.003). Other microvascular parameters did not differ between groups.

CONCLUSION

Cardiovascular risk factors and a microcirculation abnormality (papillae rectification) were significantly increased in young non-diabetic women with pGDM.

Nailfold capillary abnormalities in sclerodermatous chronic GVHD

Chronic GVHD (cGVHD) complicating allo-SCT commonly presents as sclerotic skin changes resembling systemic sclerosis (SSc), suggesting a common pathophysiological pathway. Damage to capillaries is considered an early event in the pathogenesis of SSc, and is associated with characteristic nailfold capillary abnormalities. Whether such nailfold capillary abnormalities occur in sclerodermatous cGVHD is unknown. Nailfold videocapillaroscopy (NVC) was used to evaluate capillary morphology, density and loop dimensions in 14 patients with sclerodermatous cGVHD, 14 sex- and age-matched SSc patients, and 14 healthy controls. It was shown that none of the cGVHD patients and controls, whereas all SSc patients showed severe capillary abnormalities. cGVHD patients and controls showed no differences in capillary density (9.05 vs 9.16 loops/mm, respectively, P=0.84), and capillary loop dimensions (total loop width 44.36 vs 45.56 μm, respectively, P=0.84). Compared with cGVHD patients, SSc patients had a reduced capillary density (9.05 vs 5.25 loops/mm, respectively, P<0.001), and an increase in capillary loop dimensions (total loop width 44.36 vs 99.97 μm, respectively, P=<0.001). In conclusion sclerodermatous cGVHD patients do not show the characteristic microvascular abnormalities seen in SSc, suggesting that capillary damage does not contribute to the pathophysiology of sclerodermatous cGVHD, and making NVC unsuitable for early identification.

Nailfold capillary patterns in healthy subjects: a real issue in capillaroscopy

Nailfold capillaroscopy has been extensively applied in a broad spectrum of pathologic conditions, but very few data have been published in healthy individuals. The aim of this study was to describe the nailfold capillary findings on a large series of healthy subjects using the video-capillaroscopy technique. Nailfold capillaries were studied based on their morphology, dimensions and density. Then, to evaluate jointly the association between different capillary findings in groups of subjects which were homogeneous for their characteristics, cluster analysis was performed. The results (median) of capillary measurements were as follows: loop length 207μm, external diameter 39μm, internal diameter 17μm, apical diameter 17μm, and intercapillary distance 143μm. Based on the cluster analysis three major "normal" morphologic capillaroscopic patterns were depicted: 1) the "normal" pattern mainly with 2 to 5 U-shaped loops/mm and ≤2 tortuous loops/mm; 2) the "perfect normal" pattern with ≥5 U-shaped loops/mm and 3) the "unusual normal" with at least 1 meandering or bushy loop, or at least 1 microhemorrhage, or with >4 crossed loops/mm. Regarding the loop measurements, the majority of subjects had a median of 7capillaries/mm with a median length of 198μm.