Quantitative analysis of conjunctival microvasculature imaged using optical coherence tomography angiography

Qualitative and quantitative comparison of two semi-manual retinal vascular density analyzing methods on optical coherence tomography angiography images of healthy individuals

The aim of this study was to evaluate qualitative and quantitative differences in vascular density analysis of an established and a novel alternative for post-processing on optical coherence tomography angiography (OCTA) images in healthy individuals. OCTA examinations of 38 subjects were performed. After extracting the images, two semi-manual post-processing techniques, the already established Mexican hat filtering (MHF) and an alternative, the Shanbhag thresholding (ST) were applied. We assessed Vessel Density (VD), Skeleton Density (SkD) and Vessel Diameter Index (VDI). We analyzed the results in order to establish similarities or potentially relevant differences. Regarding SkD and VD, MHF generally gave higher values than ST. Simultaneously, mean values were also predominantly higher by MHF; however, standard deviations (SD) were higher by ST (range [mean ± SD]: 0.054 ± 0.038 to 0.134 ± 0.01 and 0.134 ± 0.095 to 0.362 ± 0.028 vs 0.012 ± 0.014 to 0.087 ± 0.03 and 0.039 ± 0.047 to 0.4 ± 0.095 for SkD and VD with MHF vs SkD and VD with ST, respectively). Values of VDI were considerably higher with ST than with MHF, while standard deviation was still significantly higher with ST (range [mean ± SD]: 2.459 ± 0.144 to 2.71 ± 0.084 and 2.983 ± 0.929 to 5.19 ± 1.064 for VDI with MHF and ST, respectively). The noise level reduction of the two methods were almost identical (noise levels: 65.8% with MHT and 65.24% with ST). Using MHF, the vascular network gets more fragmented by an average of 40% compared to ST. Both methods allow the segmentation of the vascular network and the examination of vascular density parameters, but they produce largely inconsistent results. To determine if these inconsistent results are clinically meaningful, and which method is more suitable for clinical use, our results provide further evidence that detailed understanding of the image analysis method is essential for reliable decision making for patients with retinal pathology. For longitudinal monitoring, use of the same image processing method is recommended.

Current clinical applications of anterior segment optical coherence tomography angiography: a review

Optical coherence tomography (OCT) is a revolutionary in vivo imaging technology that presents real-time information on ocular structures. Angiography based on OCT, known as optical coherence tomography angiography (OCTA), is a noninvasive and time-saving technique originally utilized for visualizing retinal vasculature. As devices and built-in systems have evolved, high-resolution images with depth-resolved analysis have assisted ophthalmologists in accurately localizing pathology and monitoring disease progression. With the aforementioned advantages, application of OCTA has extended from the posterior to anterior segment. This nascent adaptation showed good delineation of the vasculature in the cornea, conjunctiva, sclera, and iris. Thus, neovascularization of the avascular cornea and hyperemia or ischemic changes involving the conjunctiva, sclera, and iris has become prospective applications for AS-OCTA. Although traditional dye-based angiography is regarded as the gold standard in demonstrating vasculature in the anterior segment, AS-OCTA is expected to be a comparable but more patient-friendly alternative. In its initial stage, AS-OCTA has exhibited great potential in pathology diagnosis, therapeutic evaluation, presurgical planning, and prognosis assessments in anterior segment disorders. In this review of AS-OCTA, we aim to summarize scanning protocols, relevant parameters, and clinical applications as well as limitations and future directions. We are sanguine about its wide application in the future with the development of technology and refinement in built-in systems.

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.

Performance Assessment of Two Different Approaches of Measuring Skeletonized Radial Peripapillary Capillary Vessel Density in Glaucoma Patients

Objective

To compare performance assessment of two methods of measuring radial peripapillary capillary (RPC) vessel density (VD) after skeletonization using MATLAB and Image J in glaucoma clinical setting.

Methods

Seventy-three eyes of 73 glaucoma patients from Beijing Tongren Hospital were included in this prospective study. Original images of RPC were obtained using optical coherence tomography angiography. Two approaches were executed before measuring. Method 1 (M1) required image sharpening, removal of big vessels, and skeletonization. Method 2 (M2) required skeletonization and removal of major vessels. Each method was executed twice. Repeatability and correlations with glaucomatous parameters were assessed. Factors associated with retinal nerve fiber layer thickness (RNFLT) and visual field mean deviation (MD) were analyzed.

Results

Average VD was 13.86 ± 2.73 and 7.50 ± 2.50% measured by M1 and M2. Percentage of total elimination of the major vessels was 36.99 and 100% by M1 and M2, respectively. The intrasession and intersession reproducibility was higher by M2 (ICC = 0.979, ICC = 0.990) than by M1 (ICC = 0.930, ICC = 0.934). VD measured by M2 showed stronger correlations with glaucomatous parameters than by M1. By stepwise multiple linear regression, thinner RNFLT was associated with smaller VD measured by M2 (B = 4.643, P < 0.001). Worse MD was associated with smaller VD measured by M1 (B = 1.079, P = 0.015).

Conclusion

The VD measured by M2 showed better reproducibility and higher correlation with glaucomatous structural parameters. Image sharpning helps display of hazy vasculature in glaucoma, which may reflect visual function better. Researchers should carefully choose image processing methods according to their research object.

[Use of optical coherence tomography angiography in assessment in conjunctival vascular architecture in health and pathology]

PURPOSE

Investigation of the capabilities of anterior segment (AS) optical coherence tomography angiography (OCTA) in evaluation of conjunctival vascular architecture in healthy individuals and in various pathological conditions.

MATERIAL AND METHODS

The study included 17 healthy volunteers (34 eyes; the control group) and 62 patients (68 eyes) with conjunctival lesions of various nature. All participants underwent AS-OCT and AS-OCTA with assessment of qualitative (vessels pattern, lumen, pathologic tortuosity) and quantitative parameters (vessel density (VD, %) in the lesion area). Mean VD (MVD) and local VD (LVD) were determined, as well as VD in perifocal tissues (PVD).

RESULTS

OCTA scans in 8 conjunctival sectors showed mostly radial pattern of the vascular architecture, with vessel lumen remaining the same over their entire visible length. Larger-sized vessels in deeper conjunctival layers were discovered in most cases. The lowest VD value (33.3%) was registered in the superotemporal quadrant, and the highest (38.9%) - in the nasal. Tortuosity of the vessels with course disruption, uneven lumen over the length of the vessels and increase in VD were observed in the area of conjunctival lesions in all cases excluding congenital abnormalities, pingueculae and conjunctival melanocytic intraepithelial neoplasia. The malignant nature of the tumors was indicated by dense vessel distribution and difficulties for visualization of intravascular space, and confirmed by pathohistological analysis. An increase in the number of areas with a lace-like pattern was characteristic for melanomas, with mean VD of more than 50% in the most vascularized areas.

CONCLUSION

AS-OCTA is an informative method for the visualization of vessels in healthy conjunctiva and in conjunctival pathology. Local VD in the lesion area should be measured when the vessels are unevenly distributed.

Plasminogen deficiency causes reduced angiogenesis and behavioral recovery after stroke in mice

Plasminogen is involved in the process of angiogenesis; however, the underlying mechanism is unclear. Here, we investigated the potential contribution of plasmin/plasminogen in mediating angiogenesis and thereby contributing to functional recovery post-stroke. Wild-type plasminogen naive (Plg^+/+) mice and plasminogen knockout (Plg^-/-) mice were subjected to unilateral permanent middle cerebral artery occlusion (MCAo). Blood vessels were labeled with FITC-dextran. Functional outcomes, and cerebral vessel density were compared between Plg^+/+ and Plg^-/- mice at different time points after stroke. We found that Plg^-/- mice exhibited significantly reduced functional recovery, associated with significantly decreased vessel density in the peri-infarct area in the ipsilesional cortex compared with Plg^+/+ mice. In vitro, cerebral endothelial cells harvested from Plg^-/- mice exhibited significantly reduced angiogenesis assessed using tube formation assay, and migration, as evaluated using Scratch assays, compared to endothelial cells harvested from Plg^+/+ mice. In addition, using Western blots, expression of thrombospondin (TSP)-1 and TSP-2 were increased after MCAo in the Plg^-/- group compared to Plg^+/+ mice, especially in the ipsilesional side of brain. Taken together, our data suggest that plasmin/plasminogen down-regulates the expression level of TSP-1 and TSP-2, and thereby promotes angiogenesis in the peri-ischemic brain tissue, which contributes to functional recovery after ischemic stroke.

Laser Doppler holography of the anterior segment for blood flow imaging, eye tracking, and transparency assessment

Laser Doppler holography (LDH) is a full-field blood flow imaging technique able to reveal human retinal and choroidal blood flow with high temporal resolution. We here report on using LDH in the anterior segment of the eye without making changes to the instrument. Blood flow in the bulbar conjunctiva and episclera as well as in corneal neovascularization can be effectively imaged. We additionally demonstrate simultaneous holographic imaging of the anterior and posterior segments by simply adapting the numerical propagation distance to the plane of interest. We used this feature to track the movements of the retina and pupil with high temporal resolution. Finally, we show that the light backscattered by the retina can be used for retro-illumination of the anterior segment. Hence digital holography can reveal opacities caused by absorption or diffusion in the cornea and eye lens.

Imaging of vascular abnormalities in ocular surface disease

The vascular system of the ocular surface plays a central role in infectious, autoimmune, inflammatory, traumatic and neoplastic diseases. The development, application, and monitoring of treatments for vascular abnormalities depends on the in vivo analysis of the ocular surface vasculature. Until recently, ocular surface vascular imaging was confined to biomicroscopic and color photographic assessment, both limited by poor reproducibility and the inability to image lymphatic vasculature in vivo. The evolvement and clinical implementation of innovative imaging modalities including confocal microscopy, intravenous, and optical coherence tomography-based angiography now allows standardized quantitative and functional vascular assessment with potential applicability to automated analysis algorithms and diagnostics.

Transient effect of suction on the retinal neurovasculature in myopic patients after small-incision lenticule extraction

PURPOSE

To characterize retinal neurovasculature changes after small-incision lenticule extraction (SMILE) in myopic patients.

SETTING

Ophthalmic Center, the Second Affiliated Hospital of Guangzhou Medical University, China.

DESIGN

Prospective interventional study.

METHODS

The corrected distance visual acuity/uncorrected distance visual acuity, corrected intraocular pressure (CIOP), and corneal tomography were evaluated at baseline (PRE), postoperative day (POD) 1, and POD 7. Ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were measured. The vessel area densities (VADs, %), vessel skeleton densities (VSDs, %), vessel diameter index (VDI), and fractal dimensions (Dbox) of the superficial vascular plexus (SVP) and deep vascular plexus (DVP) were measured in a circular area (ϕ 2.5 mm) centered on the fovea.

RESULTS

A total of 38 myopic patients were recruited. The GCIPL thickness was increased after SMILE at POD 1 and POD 7 (P < .01) but no significant changes in the pRNFL thickness. The VAD, VSD, and Dbox of the SVP were decreased at POD 1 (P < .01), but not at POD 7. The VDI in small vessels of the SVP and DVP was decreased at POD 1 (P < .05) and increased at POD 7 (P < .05). Changes in CIOP were positively correlated with changes in the GCIPL thickness. Changes in CIOP were negatively correlated with changes in the VAD of small vessels and the Dbox of total vessels in the DVP. Changes in CIOP were negatively correlated with the VSD and VDI of small vessels in the DVP and changes in the VDI of big vessels in the SVP.

CONCLUSIONS

The transient fluctuations in the retinal neurovasculature after SMILE may represent a characteristic homeostasis pattern in patients after refractive surgery.

Anterior Segment OCTA of Melanocytic Lesions of the Conjunctiva and Iris

PURPOSE

To study the feasibility and diagnostic value of vascular imaging using optical coherence tomography (OCT)-angiography (OCTA) of melanocytic lesions of the conjunctiva and iris.

DESIGN

Cross-sectional study.

METHODS

Twenty-five patients with an untreated conjunctival lesion (5 melanoma, 13 nevus, 7 primary acquired melanosis [PAM]) and 52 patients with an untreated iris lesion (10 melanoma, 42 nevus) were included. Patients were imaged using a commercially available OCTA device, with the addition of an anterior segment lens and manual focussing. Tumor vessel presence, vascular patterns and vascular density were assessed.

RESULTS

Good OCTA images were obtained in 18 of 25 conjunctival lesions and 42 of 52 iris lesions. Failure was caused by lack of patient cooperation, an unfavorable location, or mydriasis. In all imaged conjunctival lesions and 77% of iris lesions, vascular structures were detected. Conjunctival melanoma and nevi demonstrated the same intralesional tortuous patterns, whereas vasculature in eyes with PAM was similar to normal conjunctiva. Both iris melanoma and nevi demonstrated tortuous patterns, distinct from the radially oriented normal iris vasculature.

CONCLUSIONS

Optical coherence tomography angiography (OCTA) allows for noninvasive imaging of the vasculature in melanocytic lesions of the conjunctiva and iris. Good image quality depends highly on patient cooperation and lesion characteristics. Differentiation of benign and malignant lesions was not possible. New software is called for to improve image acquisition and analysis.

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.

Vascular Density of the Anterior Segment of the Eye Determined by Optical Coherence Tomography Angiography and Slit-Lamp Photography

<b><i>Objective:</i></b> To determine the vascular density of the anterior segment (AS) of the eye from optical coherence tomography angiography (OCTA) images and slit-lamp photographs. <b><i>Methods:</i></b> A swept-source OCTA (Plex Elite 9000; Carl Zeiss) device modified with a +10-diopter lens was used to record the vasculature of the AS. Twenty eyes, including 4 eyes of 4 healthy subjects and 16 eyes of 12 patients scheduled for cataract surgery or combined vitrectomy and cataract surgery, were studied. The slit-lamp photographs of the AS were acquired concurrently with the AS-OCTA images. The vascular density was measured preoperatively and postoperatively in the nasal, temporal, superior, and inferior quadrants after binarization with ImageJ software. <b><i>Results:</i></b> Acceptable AS-OCTA images were obtained of 65% (superior), 80% (nasal), 70% (inferior), and 80% (temporal) of the eyes. The percentage of acceptable images was significantly lower in the superior quadrant among the AS-OCTA images than among the AS photographs (100%; <i>p</i> = 0.004). The vascular density determined by AS-OCTA was higher than that determined in the AS photographs in all quadrants (<i>p</i> = 0.011 to &#x3c;0.001). The AS-OCTA B-mode images showed that vascular flow was identified mainly between the conjunctiva and sclera but not in the ciliary body. The vascular density increased significantly after cataract surgery in the superior quadrant, which was significantly correlated with the location of the surgical incision (<i>p</i> = 0.03). <b><i>Conclusion:</i></b> AS-OCTA can obtain images with higher vascular density of the conjunctiva and sclera than slit-lamp photographs, and AS-OCTA images can show a postoperative increase in vascular density.