Functional OCT reveals anisotropic changes of retinal flicker-evoked vasodilation.

The purpose of this study is to verify the effect of anisotropic property of retinal biomechanics on vasodilation measurement. A custom-built optical coherence tomography (OCT) was used for time-lapse imaging of flicker stimulation-evoked vessel lumen changes in mouse retinas. A comparative analysis revealed significantly larger (18.21%) lumen dilation in the axial direction compared to the lateral (10.77%) direction. The axial lumen dilation predominantly resulted from the top vessel wall movement toward the vitreous direction, whereas the bottom vessel wall remained stable. This observation indicates that the traditional vasodilation measurement in the lateral direction may result in an underestimated value.

Linking Vascular Structure and Function: Image-Based Virtual Populations of the Retina.

Purpose: This study explored the relationship among microvascular parameters as delineated by optical coherence tomography angiography (OCTA) and retinal perfusion. Here, we introduce a versatile framework to examine the interplay between the retinal vascular structure and function by generating virtual vasculatures from central retinal vessels to macular capillaries. Also, we have developed a hemodynamics model that evaluates the associations between vascular morphology and retinal perfusion. Methods: The generation of the vasculature is based on the distribution of four clinical parameters pertaining to the dimension and blood pressure of the central retinal vessels, constructive constrained optimization, and Voronoi diagrams. Arterial and venous trees are generated in the temporal retina and connected through three layers of capillaries at different depths in the macula. The correlations between total retinal blood flow and macular flow fraction and vascular morphology are derived as Spearman rank coefficients, and uncertainty from input parameters is quantified. Results: A virtual cohort of 200 healthy vasculatures was generated. Means and standard deviations for retinal blood flow and macular flow fraction were 20.80 ± 7.86 µL/min and 15.04% ± 5.42%, respectively. Retinal blood flow was correlated with vessel area density, vessel diameter index, fractal dimension, and vessel caliber index. The macular flow fraction was not correlated with any morphological metrics. Conclusions: The proposed framework is able to reproduce vascular networks in the macula that are morphologically and functionally similar to real vasculature. The framework provides quantitative insights into how macular perfusion can be affected by changes in vascular morphology delineated on OCTA.

Potential ocular indicators to distinguish posterior cortical atrophy and typical Alzheimer's disease: a cross-section study using optical coherence tomography angiography.

BACKGROUND: Posterior cortical atrophy (PCA) is a form of dementia that frequently displays significant visual dysfunction and relatively preserved cognitive and executive functions, thus hindering early diagnosis and treatment. This study aimed to investigate possible fundus markers in PCA patients and compare them with those of typical Alzheimer's disease (AD) patients to seek potential diagnostic patterns. METHODS: Age-matched PCA and AD patients and healthy controls (HC) completed optometry, intraocular pressure measurement, neuropsychologic assessments, optical coherence tomography (OCT), and optical coherence tomography angiography (OCTA) examination in one visit. Overall, six outcomes of thicknesses of various retinal layers and seven outcomes of the retinal microvascular network were calculated. After adjusting for age, sex, and years of education, the OCT and OCTA results were analyzed using analysis of covariance and generalized linear models. Correlation analyses were performed using Spearman correlation, and ROC curves were plotted. RESULTS: Twelve PCA patients, nineteen AD patients, and thirty HC, aged 45-80 years were included. Fifty HC, thirty AD, and twenty PCA eyes were available for foveal avascular zone (FAZ) area analysis; forty-nine HC, thirty-four AD, and eighteen PCA eyes were available for OCT and OCTA assessments. PCA patients had thinner retinal nerve fiber layer and ganglion cell layer + inner plexiform layer than HC in the 0-3 mm circle and 1-3 mm ring. Few structural differences were observed between the AD group and the other two groups. The flow area of the superficial capillary plexus and the intermediate capillary plexus was smaller in the PCA group than in the HC group in the 0-1 mm circle, 0-3 mm circle. MMSE performed better than any combination of optical parameters in identifying AD and PCA from HC (AUC = 1), while the combination of MoCA, retinal thickness and vascular density of ICP in the 1-3 mm ring, with flow area of ICP in the 0-1 mm circle showed the strongest ability to distinguish PCA from AD (AUC = 0.944). CONCLUSIONS: PCA patients exhibited similar impairment patterns to AD patients in the fundus structure and microvascular network. OCTA may aid in the non-invasive detection of AD and PCA, but still remains to be substantiated.

Quantitative evaluation of choroidal and retinal microvasculature post-alcohol consumption: A pilot study.

PURPOSE: The aim of this study was to assess the impact of acute, heavy alcohol consumption on the ocular microvasculature, providing insight into the largely unexplored response of microvascular structures to excessive drinking. METHODS: Healthy volunteers in this prospective pilot study were tasked with consuming spirits, wine, and water at different times. Alcohol intake was measured according to body weight (g/kg). The ocular microvascular parameters primarily including choroidal volume (CV) and choroidal vessel volume (CVV) reflecting arteriolovenularity, and choroidal capillary density (CCD) reflecting capillary, were evaluated using swept-source optical coherence tomography angiography at baseline and 0.5-, 1-, 2-, and 3-hour post-consumption. RESULTS: A total of 34 eyes underwent 170 successful examinations in this study. After consuming spirits or wine, we observed significant decreases in CV and CVV values (all P < 0.01 for 0.5-, 1-, 2-, and 3-hour post-consumption), along with significant increase in CCD (P < 0.05 at 0.5-, 1-, 2-hour post-spirits consumption and 1-hour post-wine consumption). The most pronounced changes occurred 1-hour after spirits or wine consumption (all P < 0.001 in both univariate and multivariate model). However, post-consumption changes in the ocular microvasculature showed no significant differences between spirits and wine (P > 0.05). Additionally, no significant differences were observed in any parameters after water intake (all P > 0.05). CONCLUSIONS: Excessive alcohol consumption leads to ocular arteriolovenular vasoconstriction and capillary vasodilation, most evident 1-hour post-consumption of spirits and wine. Our research provides insight into alcohol's immediate ocular microvascular effects, hinting at systemic microvascular effects.

Assessment of retinal and choroidal microcirculation after unilateral recession-resection surgery for horizontal strabismus by swept-source optical coherence tomography angiography.

This study explored the possible hemodynamic changes of the retina and choroid after horizontal strabismus surgery using swept-source optical coherence tomography angiography (SS-OCTA). 32 eyes of 32 patients who underwent unilateral horizontal rectus muscle recession-resection surgery were included. SS-OCTA examinations were performed preoperatively and one week postoperatively. Several OCTA measurements were used, including vessel density (VD) of the superficial vascular complex (SVC), VD of the deep vascular complex (DVC), VD of the choriocapillaris (CC), choroidal vascular index (CVI) and choroidal thickness (CT). No significant change in VD of SVC, DVC, and CC was observed whereas CT increased significantly with CVI unchanged. Recession-resection surgery for horizontal strabismus seemed not to significantly influence the microcirculation of the retina and CC in the early postoperative period. However, choroidal thickening happened with a constant CVI probably due to the postoperative inflammation. Further studies are needed to investigate the long-term effects of unilateral recession-resection surgery for horizontal strabismus on the microcirculation of the retina and choroid.

Quantitative study of spatial and temporal variation in retinal capillary network perfusion in rat eye by in vivo confocal imaging.

Microvascular dysfunction is the underlying pathological process in many systemic diseases. However, investigation into its pathogenesis is impeded by the accessibility and complexity of the microvasculature within different organs, particularly for the central nervous system. The retina as an extension of the cerebrum provides a glimpse into the brain through which the microvasculature can be observed. Two major questions remain unanswered: How do the microvessels regulate spatial and temporal delivery to satisfy the varying cellular demands, and how can we quantify blood perfusion in the 3D capillary network? Here, quantitative measurements of red blood cell (RBC) speed in each vessel in the field were made in the in vivo rat retinal capillary network using an ultrafast confocal technique with fluorescently labelled RBCs. Retinal RBC speed and number were found to vary remarkably between microvessels ranging from 215 to 6641 microns per second with significant variations spatially and temporally. Overall, the RBC speed was significantly faster in the microvessels in the superficial retina than in the deep retina (estimated marginal means of 2405 ± 238.2 µm/s, 1641 ± 173.0 µm/s respectively). These observations point to a highly dynamic nature of microvasculature that is specific to its immediate cellular environment and is constantly changing.

Changes in retinal and choroidal blood flow after one or two horizontal rectus muscle surgeries by optical coherence tomography angiography.

PURPOSE: To evaluate the retinal and choroidal microvasculature after one or two horizontal rectus muscle surgeries in strabismus patients using swept-source optical coherence tomography angiography (SS-OCTA). METHODS: 30 eyes of 26 patients who underwent horizontal rectus muscle surgery were included in this study. Group A, A' and Group B , B' respectively consisted preoperative and postoperative measurements of patients who underwent one or two horizontal rectus muscle surgeries. We analyzed the vessel density (VD) of the superficial vascular complex (SVC), the deep vascular complex (DVC), the choriocapillary layer (CC), choroidal vascular index (CVI), choroidal thickness (T-Ch) and retinal nerve fiber layer thickness (T-RNFL) preoperatively, and one week postoperatively. RESULTS: Only in the nasal sector of the perifoveal zone, the VD in SVC demonstrated a significant increase in Group A' (p = 0.027). There was a statistically significant difference in the VD changes of SVC between Group A and Group B (p = 0.043). The VD in DVC did not change significantly in the whole macular compared with the preoperative. Moreover, in both Group A' and Group B', the VD in CC showed a reduction in a single sector of the parafoveal area (p < 0.05). Group A' have increased CVI in the nasal sector of the perifoveal region (p = 0.008). In addition, the T-Ch increase in the perifoveal region was more significant in Group B' than in Group A' (p < 0.05). Group A' showed statistically significant decreases in T-RNFL in the foveal and parafoveal regions (p < 0.05). CONCLUSION: This study revealed that the increase in choroidal thickness was more significant after two rectus muscle surgery. In addition, there were microvascular changes in sectional macular regions after strabismus surgery. OCTA is an excellent way to study the impact of strabismus surgery on the macular structure and blood flow.

We used SS-OCTA, which provided more objective and accurate measurements, to assess macular vessel density and thickness of retinal and choroid after one or two horizontal rectus muscle surgeries.

Flow Heterogeneity and Factors Contributing to the Variability in Retinal Capillary Blood Flow.

Purpose: Capillary flow plays an important role in the nourishment and maintenance of healthy neural tissue and can be observed directly and non-invasively in the living human retina. Despite their importance, patterns of normal capillary flow are not well understood due to limitations in spatial and temporal resolution of imaging data. Methods: Capillary flow characteristics were studied in the retina of three healthy young individuals using a high-resolution adaptive optics ophthalmoscope. Imaging with frame rates of 200 to 300 frames per second was sufficient to capture details of the single-file flow of red blood cells in capillaries over the course of about 3 seconds. Results: Erythrocyte velocities were measured from 72 neighboring vessels of the parafoveal capillary network for each subject. We observed strong variability among vessels within a given subject, and even within a given imaged field, across a range of capillary flow parameters including maximum and minimum velocities, pulsatility, abruptness of the systolic peak, and phase of the cardiac cycle. The observed variability was not well explained by "local" factors such as the vessel diameter, tortuosity, length, linear cell density, or hematocrit of the vessel. Within a vessel, a moderate relation between the velocities and hematocrit was noted, suggesting a redistribution of plasma between cells with changes in flow. Conclusions: These observations advance our fundamental understanding of normal capillary physiology and raise questions regarding the potential role of network-level effects in explaining the observed flow heterogeneity.

High-speed measurement of retinal arterial blood flow in the living human eye with adaptive optics ophthalmoscopy.

We present a technique to measure the rapid blood velocity in large retinal vessels with high spatiotemporal resolution. Red blood cell motion traces in the vessels were non-invasively imaged using an adaptive optics near-confocal scanning ophthalmoscope at a frame rate of 200 fps. We developed software to measure blood velocity automatically. We demonstrated the ability to measure the spatiotemporal profiles of the pulsatile blood flow with a maximum velocity of 95-156 mm/s in retinal arterioles with a diameter >100 µm. High-speed and high-resolution imaging increased the dynamic range, enhanced sensitivity, and improved the accuracy when studying retinal hemodynamics.

Impaired retinal microcirculation in patients with non-obstructive coronary artery disease.

PURPOSE: To quantitatively investigate alterations of retinal microcirculation in patients with non-obstructive coronary artery disease (NOCAD) using optical coherence tomography angiography (OCTA), and to identify the ability of retinal microcirculation parameters in differentiating coronary artery disease (CAD) subtypes. METHODS: All participants with angina pectoris underwent coronary computed tomography angiography. Patients with lumen diameter reduction of 20-50 % in all major coronary arteries were defined as NOCAD, while patients with at least one major coronary artery lumen diameter reduction ≥ 50 % were recruited as obstructive coronary artery disease (OCAD). Participants without a history of ophthalmic or systemic vascular disease were recruited as healthy controls. Retinal neural-vasculature was measured quantitatively by OCTA, including peripapillary retinal nerve fiber layer (RNFL) thickness and vessel density (VD) of the optic disc, superficial vessel plexus (SVP), deep vessel plexus (DVP), and foveal density (FD 300). p < 0.017 is considered significant in multiple comparisons. RESULTS: A total of 185 participants (65 NOCAD, 62 OCAD, and 58 controls) were enrolled. Except for the DVP fovea (p = 0.069), significantly reduced VD in all other regions of SVP and DVP was detected in both the NOCAD and OCAD groups compared to control group (all p < 0.017), while a more significant decrease was found in OCAD compared to NOCAD. Multivariate regression analysis showed that lower VD in superior hemi part of whole SVP (OR: 0.582, 95 % CI: 0.451-0.752) was an independent risk factor for NOCAD compared to controls, while lower VD in the whole SVP (OR: 0.550, 95 % CI: 0.421-0.719) was an independent risk factor for OCAD compared to NOCAD. Using the integration of retinal microvascular parameters, the area under the receiver operating characteristic curve (AUC) for NOCAD versus control and OCAD versus NOCAD were 0.840 and 0.830, respectively. CONCLUSION: Significant retinal microcirculation impairment, while milder than that in OCAD was observed in NOCAD patients, indicating retinal microvasculature assessment might provide a new systemic microcirculation observation window for NOCAD. Furthermore, retinal microvasculature may serve as a new indicator to assess the severity of CAD with good performance of retinal microvascular parameters in identifying different CAD subtypes.

New Findings in Early-Stage Keratoconus: Lamina Cribrosa Curvature, Retinal Nerve Fiber Layer Thickness, and Vascular Perfusion.

PURPOSE: Our aim was to investigate the involvement of posterior pole structures in eyes affected by keratoconus (KC). Optical coherence tomography (OCT) and OCT angiography (OCTA) were used to determine the status of lamina cribrosa (LC), peripapillary retinal nerve fiber layer (RNFL), macular and peripapillary microvasculature. DESIGN: Observational, cross-sectional, case-control analysis. METHODS: Single-center investigation involving patients with KC and healthy control subjects. Enrolled subjects underwent anterior segment OCT combined with Placido-disk topography, macular and optic nerve head swept-source OCT and swept-source OCTA scans, and 3D wide glaucoma module for peripapillary RNFL thickness measurement. The LC curvature index was used to express the degree of LC posterior bowing. We calculated the vessel density and vessel length density at the macular superficial capillary plexus, deep capillary plexus, choriocapillaris, and nerve radial peripapillary capillary plexus. RESULTS: Overall, 32 eyes with KC and an equal number of age- and axial length-matched control eyes were included in the analysis. Almost all (97%) of eyes with KC were classified as early stage. KC displayed a reduction in peripapillary RNFL thickness (104.8 ± 11.9 µm vs 110.7 ± 10.5 µm; P = .039) and nerve radial peripapillary capillary plexus vessel density (46.31% ± 3% vs 43.82% ± 4%; P = .006) when compared with control subjects; these differences were more evident in the temporal sector and were associated with a higher LC curvature index (9.9% ± 2.6% vs 8.48% ± 1.7%; P = .012). Mean macular superficial capillary plexus vessel density was 3 percentage points lower in eyes with KC than in healthy controls (P < .001). CONCLUSION: Early-stage KC may be characterized by a posterior bowing of the LC along with a subtle peripapillary RNFL thinning and vascular impairment. These findings support the hypothesis that KC may be a corneal manifestation of a more generalized "eye collagen disease."

Evaluation of the Optic Nerve Head Using Optical Coherence Tomography Angiography in Systemic Sclerosis Patients.

PURPOSE: To quantify microvascular vessel density in the optic disc using optical coherence tomography angiography (OCTA) in patients with systemic sclerosis (SS); to determine whether there is a difference in values between patients and controls; and to correlate the OCTA measurements with disease activity, damage risk, and drug usage. METHODS: Patients aged 20 - 76 years who were followed up after a diagnosis of SS and age- and gender-matched controls. The patients underwent RTVue-XR AngioVue OCTA imaging in this cross-sectional observational study. RESULTS: A total of 61 eyes of 61 consecutive SS patients and 60 eyes of 60 controls were investigated. There was no statistically significant difference between the patients and control groups regarding the average RNFL (retinal fiber layer) and radial peripapillary capillary (RPC) vessel density (VD) measurements (p = 0.35, p = 0.25, respectively). As the antinuclear antibody (ANA) titer increased, RNFLsuperior (p = 0.01, r = - 0.327), RPCwhole (p = 0.029, r = 0.279), RPCperipapillary (p = 0.037, r = - 0.267), RPCsuperior (p = 0.003, r = - 0.371), and RPCinferior (p = 0.02, r = 0.297) values decreased with statistical significance. The RPCinside values were lower in anti-Scl-70-positive patients compared to patients negative for anti-Scl-70 (topoisomerase I) (p = 0.021). The RNFLnasal (p = 0.03, r = - 0.278) value decreased as the years of disease increased. The RPCinside value was higher in patients using hydroxychloroquine and calcium channel blockers than those who did not use them (p = 0.021 and p = 0.027, respectively). The RPCwhole, RPCperipapillary, and RPCnasal values were higher, with statistical significance in corticosteroid users than in those patients who did not use corticosteroids (p = 0.043, 0.030, and 0.033, respectively). CONCLUSION: There was no significant difference between the patients and control groups regarding the average RPC VD measurements. However, since this is the first study to analyze optic disc vessel density in SS patients, optic nerve blood flow changes in scleroderma with OCTA could be studied.

Effects of B12 Deficiency Anemia on Radial Peripapillary and Macular Vessel Density: An Optical Coherence Tomography Angiography (OCTA) Study.

BACKGROUND: To evaluate the macular and optic disc vascular changes in vitamin B12 deficiency anemia. METHODS: A total of 24 patients with vitamin B12 deficiency anemia and 24 healthy controls were involved in this study. All participants were evaluated for central macular thickness (CMT), peripapillary retina nerve fiber layer (RNFL) thickness, foveal avascular zone (FAZ) area, macular vessel density (VD) in superficial capillary plexus (SCP) and deep capillary plexus (DCP), choriocapillaris flow area, and optic disc radial peripapillary capillary (RPC) VD using optic coherence tomography (OCT) and optic coherence tomography angiography (OCTA). Metabolic parameters were also noted. RESULTS: Temporal RNFL thickness significantly decreased in the B12 deficiency anemia group (p = 0.04). Choriocapillaris flow area (p = 0.045) and macular vessel density in both SCP (p = 0.022) and DCP (p = 0.018) markedly declined in the study group. Optic disc RPC VD in the B12 deficiency anemia group was lower in all regions compared to that of the control group, but the difference was not statistically significant (p > 0.05). There were significant positive correlations between choriocapillaris flow area, macular VD, vitamin B12, and hemoglobin. CONCLUSION: Retinal vascular alterations were observed in B12 deficiency anemia, and OCTA may be beneficial in the diagnosis and follow-up of ocular complications in these cases.

Optical Coherence Tomography Angiography in Posner-Schlossman Syndrome - A Preliminary Study.

PURPOSE: To evaluate vessel density (VD) and structural features in Posner-Schlossman syndrome (PSS) patients' eyes using optical coherence tomography angiography (OCTA). METHODS: An observational study was conducted among 23 affected eyes (group A), 23 contralateral unaffected eyes (group B), and 23 control eyes (group C). RESULT: The macular superficial, macular deep, and optic nerve head (ONH) VD of group A were 45.26 ± 5.80, 46.78 ± 6.96, and 46.10 ± 4.22, respectively. The macular superficial VD, macular deep VD, and retinal thickness of group A were significantly lower than those of group C (all P < .05). The retinal nerve fiber layer thickness of group A decreased in the superior and inferior sections. The macular superficial VD had the highest diagnostic value (area under curve = 0.989) for PSS. CONCLUSION: OCTA can detect the fundus change in the macular and ONH regions of the PSS's affected eyes.

Evaluation of the optic nerve head and macular vessel density in keratoconus patients using optical coherence tomography angiography- a cross-sectional study.

PURPOSE: Our study evaluated macular and optic disc vascular density (VD) changes in patients diagnosed with keratoconus, as compared with gender and age-matched healthy controls, in relation to the keratoconus stage. METHODS: This comparative cross-sectional study included adult patients who received a diagnosis of keratoconus at the Cornea Clinic. All scans consisted of two 4.5 mm × 4.5 mm images of the optic disc area and 6 × 6 mm images of the macular area using optical coherence tomography angiography. RESULTS: The study included 67 patients (26 women (38.8%) and 41 men (61.2%)) and 74 controls (31 women (41.9%) and 43 men (58.1%)). The mean ages of the keratoconus group and the control group were 30.0 ± 8.0 and 31.1 ± 7.5, respectively. Macular VD (whole, superficial, and deep) and peripapillary VD (whole) values were decreased statistically significant compared with the control group (p < 0.01 and p = 0.015, respectively). The keratoconus stage was negatively correlated with both the macular VD (p = 0.048, r = -0.314) and whole-peripapillary VD values (p = 0.03, r = -0.34). CONCLUSION: Keratoconus might affect the posterior and anterior segments due to similar etiologies, including diminished collagen quality. Therefore, examination of the posterior segment should be performed thoroughly in keratoconus patients.

The effect of postmenopausal hormonal drop on optic nerve head and peripapillary perfusion using optical coherence tomography angiography (OCTA).

We studied the effect of menopause with subsequent estrogen drop on optic nerve head structure and peripapillary vasculature. This cross-sectional analytic study was carried out on 100 eyes of 100 patients; patients were divided into a premenopausal group (50 eyes) and a postmenopausal group (50 eyes). Optical coherence tomography was done to evaluate retinal nerve fiber layer thickness (RNFLT) and optical coherence tomography angiography (OCTA) to assess the peripapillary capillary vessel density. RNFLT as well as the peripapillary vessel density (VD) were significantly lower in the postmenopausal group (P value < 0.001) with increasing age, hormonal drop, and higher intraocular pressure (IOP), specifically in the inferior quadrant. However, the negative correlation between IOP and VD (r = - 0.541) was stronger than its negative correlation with RNFLT (r = - 0.318). Postmenopausal hormonal changes lead to a significant rise in IOP-although still not glaucomatous- and a decrease in the RNFLT and perfusion of the optic nerve. This confirms the relation between hormonal drop and glaucoma in postmenopausal women. Changes in peripapillary vascular density were more evident than RNFL in correlation with IOP and age changes. So, OCTA can be used to detect early optic nerve affection.

THE ROLE OF OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN PATIENTS WITH PREECLAMPSIA.

PURPOSE: To investigate the changes in the microvascular structure of the retina and optic disk by comparing the optical coherence tomography angiography findings in preeclamptic patients with those in healthy pregnant women and healthy nonpregnant women and also to evaluate the preeclamptic patients after delivery by showing whether the changes are permanent or not. METHODS: Fifty preeclamptic, 50 healthy pregnant, and 50 healthy nonpregnant women enrolled in three groups (preeclamptic pregnant women group, healthy pregnant women group, and nonpregnant women group; respectively). Patients in the preeclamptic pregnant women group were evaluated at three different time points including up to 3 hours before delivery (Group 1), 2, or 3 days after delivery (Group 2), and 6 weeks after delivery (Group 3), and compared with each other. All patients underwent a comprehensive ophthalmologic examination including optical coherence tomography angiography. RESULTS: Choriocapillaris blood flow area, deep foveal density, deep temporal density, deep nasal density, and radial peripapillary capillary inside disk density values were significantly lower in the preeclamptic pregnant women group than in the healthy pregnant women group. Deep foveal density and deep nasal density values were significantly higher in Group 3 than in Group 1 and 2, and deep temporal density was significantly higher in Group 3 than in Group 1. CONCLUSION: Optical coherence tomography angiography diagnosed decreased deep retinal capillary density values in the macula of patients with preeclampsia, but these results improved after delivery.

Investigation of the short-term effects of water drinking test on the eye using optical coherence tomography angiography in young healthy male subjects.

PURPOSE: To evaluate the acute effects of the water drinking test (WDT) on the eye using optical coherence tomography angiography (OCTA) on healthy young male subjects. METHODS: The study included 25 eyes of 25 male subjects. Selected parameters of the retinal vasculature were measured, including macular flow indices, foveal avascular zone, and vessel densities (VDs) of the macula using OCTA. The measurements were taken on the first day without drinking water at 0 min, 30 min and 60 min, then repeated on the second day before drinking water at 0 min, and after drinking water at 30 min and 60 min. The Paired Samples t-test and repeated measures One-way analysis of variance test were used in the statistical analyses. RESULTS: The repeated measures analysis of variance test using Bonferroni adjustment demonstrated a significant increase in superficial and deep foveal VD following WDT (p < 0.001 for both). Intraocular pressure, retinal nerve fibre layer thickness, foveal avascular zone, flow area of choriocapillaris, flow area of outer retina, foveal non-flow area of superficial layer, and retinal thickness measurements showed no significant changes following WDT. CONCLUSIONS: WDT is associated with temporary flow modifications in superficial and deep foveal vascular plexus in young male subjects.

Intraocular vascular analysis using optical coherence tomography angiography in patients with vascular paralytic strabismus.

PURPOSE: To investigate changes in peripapillary and macular vessel density (VD) in vascular paralytic strabismus using optical coherence tomography angiography (OCTA). METHODS: Medical records of patients who recovered from monocular vascular paralytic strabismus were retrospectively analyzed. Age, sex, presence of underlying diseases, strabismus type and severity, time to recovery, and visual acuity at diagnosis were evaluated. VD in the optic disc area and macular capillary plexus density were estimated using OCTA. The effect of paralytic strabismus on intraocular VD was investigated by comparing VD between the paralysis and contralateral eyes. To analyze hemodynamic changes, VD changes in the paralysis eye during the attack and recovery were compared. RESULTS: Thirty-one patients (mean age, 64.1±13.0 years; 21 males, 10 females) were included and mean recovery time was 3.0±1.6 months. The most common paralysis was sixth nerve palsy (54.8%). When comparing OCTA results between the paralysis and contralateral non-paralysis eyes, foveal VD in the superficial capillary plexus (SCP) was significantly lower in the paralysis eye (P = 0.034); however, VD in the optic disc area was not different. In the paralysis eye, foveal VD in the SCP significantly increased after paralysis recovery (P = 0.04). During attack, the maximal deviation angle and severity of duction limitation were significantly related to foveal VD in SCP. The greater the deviation angle and the more severe the eye movement restriction, the lower the foveal VD in SCP. CONCLUSIONS: Transient retinal ischemia of the paralysis eye was observed in a patient with paralytic strabismus, which corresponded to the degree of deviation angle and ocular motor restriction. Ischemic factors, which are the etiology of vascular paralytic strabismus, affect intraocular blood flow.

Using the dynamic forward scattering signal for optical coherence tomography based blood flow quantification.

To our knowledge, all existing optical coherence tomography approaches for quantifying blood flow, whether Doppler-based or decorrelation-based, analyze light that is back-scattered by moving red blood cells (RBCs). This work investigates the potential advantages of basing these measurements on light that is forward-scattered by RBCs, i.e., by looking at the signals back-scattered from below the vessel. We show experimentally that flowmetry based on forward-scattering is insensitive to vessel orientation for vessels that are approximately orthogonal to the imaging beam. We further provide proof-of-principle demonstrations of dynamic forward-scattering (DFS) flowmetry in human retinal and choroidal vessels.