Retinal venous pulsation: Expanding our understanding and use of this enigmatic phenomenon

Changes in vascular resistance with intraocular pressure and damage severity in experimental glaucoma

There is evidence of changes in retinal hemodynamics in both experimental glaucoma and human disease. A major potential confound is that intraocular pressure (IOP) may also be directly affecting vascular resistance and/or the vasodilatory capacity of vessels in the optic nerve head and retina. This is particularly problematic in experimental glaucoma, where chronic IOP elevation is maintained, without the IOP-reducing medications typically used by patients involved in human studies. However, those animal studies remain invaluable, due to the possibility of extensive baseline testing in the knowledge that no glaucomatous loss has commenced, and due to the degree of control that is possible over parameters such as medication regimens. In this study, we aim to assess the impact of chronic IOP elevation on vascular resistance parameters, and separate it from the impact of glaucomatous damage severity. Longitudinal measurements were made using laser speckle flowgraphy before and after unilateral IOP elevation in 31 non-human primates. The pulsatile waveform was extracted and used to calculate the pulsatility index (maximum minus minimum, as a proportion of the mean) and resistivity index (maximum flow minus minimum flow, as a proportion of the maximum), in both the major vessels and the other tissue within the optic nerve head, for an average of 18 time points per animal. The vascular resistance indices increased with IOP at both locations, both in the full dataset, and in the subset of data points restricted to the visit at which IOP first exceeded 30 mmHg until the resistance index reached its maximum for that eye (all p < 0.001). After adjusting for the influence of IOP using coefficients from linear mixed effects models, the resistance indices exhibited non-monotonic relations with damage severity, first increasing from baseline, but then decreasing back to or beyond the normal range in eyes with more severe damage. Further studies are needed to accurately characterize the location and timing of these changes during the course of glaucomatous damage, which would help identify the pathophysiologic processes that are underway at different stages of the disease.

Calculation of vessel pulse wave velocities in retinal vein segments within the optic disc centre

The carotid-femoral pulse wave velocity (PWV) method is used clinically to determine degrees of stiffness and other indices of disease. It is believed PWV measurement in retinal vessels may allow early detection of diseases. In this paper we present a new non-invasive method for estimating PWVs in retinal vein segments close to the optic disc centre, based on the measurement of blood column pulsation in retinal veins (reflective of vessel wall pulsation), using modified photoplethysmography (PPG). An optic disc (OD) PPG video is acquired spanning three cardiac cycles for a fixed ophthalmodynamometric force. The green colour channel frames are extracted, cropped and aligned. A harmonic regression model is fitted to each pixel intensity time series along the vein centreline from the centre to the periphery of the OD. The phase of the first harmonic is plotted against centreline distance. A least squares line is fitted between the first local maximum phase and first local minimum phase and its slope used to compute PWV. Five left eye inferior hemi-retinal veins from five healthy subjects were analysed. Velocities were calculated for several induced intraocular pressures ranging from a mean baseline of 14 mmHg (SD 5) to 56 mmHg in steps of approximately 5 mmHg. The median PWV over all pressure steps and subjects was 20.77 mm/s (IQR 29.27). The experimental results show that pulse wave propagation direction was opposite to flow in this initial venous segment.

Non-invasive assessment of intracranial pressure through the eyes: current developments, limitations, and future directions

Detecting and monitoring elevated intracranial pressure (ICP) is crucial in managing various neurologic and neuro-ophthalmic conditions, where early detection is essential to prevent complications such as seizures and stroke. Although traditional methods such as lumbar puncture, intraparenchymal and intraventricular cannulation, and external ventricular drainage are effective, they are invasive and carry risks of infection and brain hemorrhage. This has prompted the development of non-invasive techniques. Given that direct, non-invasive access to the brain is limited, a significant portion of research has focused on utilizing the eyes, which uniquely provide direct access to their internal structure and offer a cost-effective tool for non-invasive ICP assessment. This review explores the existing non-invasive ocular techniques for assessing chronically elevated ICP. Additionally, to provide a comprehensive perspective on the current landscape, invasive techniques are also examined. The discussion extends to the limitations inherent to each technique and the prospective pathways for future advancements in the field.

Retinal and cerebral hemodynamics redistribute to favor thermoregulation in response to passive environmental heating and heated exercise in humans

Core temperature (TC) changes, alongside exercise, affect hemodynamic responses across different conduit and microvascular beds. This study investigated impacts of ecologically valid environmental heat and exercise exposures on cerebral, skin and retinal vascular responses by combining physiological assessments alongside computational fluid dynamics (CFD) modeling. Young, healthy participants (n = 12) were exposed to environmental passive heating (PH), and heated exercise (HE) (ergometer cycling), in climate-controlled conditions (50 mins, 40°C, 50% relative humidity) while maintaining upright posture. Blood flow responses in the common carotid (CCA), internal carotid (ICA) and central retinal (CRA) arteries were assessed using Duplex ultrasound, while forearm skin microvascular blood flow responses were measured using optical coherence tomography angiography. Three-dimensional retinal hemodynamics (flow and pressure) were calculated via CFD simulation, enabling assessment of wall shear stress (WSS). TC rose following PH (+0.2°C, p = 0.004) and HE (+1.4°C, p < 0.001). PH increased skin microvascular blood flow (p < 0.001), whereas microvascular CRA flow decreased (p = 0.038), despite unchanged ICA flow. HE exacerbated these differences, with increased CCA flow (p = 0.007), unchanging ICA flow and decreased CRA flow (p < 0.001), and interactions between vascular (CCA vs. ICA p = 0.018; CCA vs. CRA p = 0.004) and microvascular (skin vs. retinal arteriolar p < 0.001) territories. Simulations revealed patterns of WSS and lumen pressure that uniformly decreased following HE. Under ecologically valid thermal challenge, different responses occur in distinct conduit and microvascular territories, with blood flow distribution favoring systemic thermoregulation, while flow may redistribute within the brain.

Precisional modulation of translaminar pressure gradients for ophthalmic diseases

The translaminar pressure gradient (TLPG) refers to two forces at the lamina cribosa of the optic nerve: the anteriorly acting intracranial pressure (ICP), and posteriorly-acting intraocular pressure (IOP). It has been proposed that controlling the translaminar pressure gradient at regular intervals may preserve the optic nerve and slow the course of glaucoma. The precisional modulation of this TLPG is a recently introduced concept that may play a role in the treatment of ophthalmic diseases such as glaucoma. In this manuscript, we review the applications of pressurized goggles on ophthalmic diseases. We also elaborate upon current investigations in modulation of the TLPG including goggles and the multi-pressure dial goggle. We discuss future research directions for ophthalmic diseases including spaceflight associated neuro-ocular syndrome (SANS), a large physiological barrier to future long-duration spaceflight.

Measurement of retinal blood flow precision in the human eye with multimodal adaptive optics imaging

Impaired retinal blood flow (RBF) autoregulation plays a key role in the development and progression of several ocular diseases, including glaucoma and diabetic retinopathy. Clinically, reproducible RBF quantitation could significantly improve early diagnosis and disease management. Several non-invasive techniques have been developed but are limited for retinal microvasculature flow measurements due to their low signal-to-noise ratio and poor lateral resolution. In this study, we demonstrate reproducible vessel caliber and retinal blood flow velocity measurements in healthy human volunteers using a high-resolution (spatial and temporal) multimodal adaptive optics system with scanning laser ophthalmoscopy and optical coherence tomography.

Synchronous functional magnetic resonance eye imaging, video ophthalmoscopy, and eye surface imaging reveal the human brain and eye pulsation mechanisms

The eye possesses a paravascular solute transport pathway that is driven by physiological pulsations, resembling the brain glymphatic pathway. We developed synchronous multimodal imaging tools aimed at measuring the driving pulsations of the human eye, using an eye-tracking functional eye camera (FEC) compatible with magnetic resonance imaging (MRI) for measuring eye surface pulsations. Special optics enabled integration of the FEC with MRI-compatible video ophthalmoscopy (MRcVO) for simultaneous retinal imaging along with functional eye MRI imaging (fMREye) of the BOLD (blood oxygen level dependent) contrast. Upon optimizing the fMREye parameters, we measured the power of the physiological (vasomotor, respiratory, and cardiac) eye and brain pulsations by fast Fourier transform (FFT) power analysis. The human eye pulsated in all three physiological pulse bands, most prominently in the respiratory band. The FFT power means of physiological pulsation for two adjacent slices was significantly higher than in one-slice scans (RESP1 vs. RESP2; df = 5, p = 0.045). FEC and MRcVO confirmed the respiratory pulsations at the eye surface and retina. We conclude that in addition to the known cardiovascular pulsation, the human eye also has respiratory and vasomotor pulsation mechanisms, which are now amenable to study using non-invasive multimodal imaging of eye fluidics.

Modelling large scale artery haemodynamics from the heart to the eye in response to simulated microgravity

We investigated variations in haemodynamics in response to simulated microgravity across a semi-subject-specific three-dimensional (3D) continuous arterial network connecting the heart to the eye using computational fluid dynamics (CFD) simulations. Using this model we simulated pulsatile blood flow in an upright Earth gravity case and a simulated microgravity case. Under simulated microgravity, regional time-averaged wall shear stress (TAWSS) increased and oscillatory shear index (OSI) decreased in upper body arteries, whilst the opposite was observed in the lower body. Between cases, uniform changes in TAWSS and OSI were found in the retina across diameters. This work demonstrates that 3D CFD simulations can be performed across continuously connected networks of small and large arteries. Simulated results exhibited similarities to low dimensional spaceflight simulations and measured data-specifically that blood flow and shear stress decrease towards the lower limbs and increase towards the cerebrovasculature and eyes in response to simulated microgravity, relative to an upright position in Earth gravity.

NLRP3-Induced NETosis: A Potential Therapeutic Target for Ischemic Thrombotic Diseases?

Ischemic thrombotic disease, characterized by the formation of obstructive blood clots within arteries or veins, is a condition associated with life-threatening events, such as stroke, myocardial infarction, deep vein thrombosis, and pulmonary embolism. The conventional therapeutic strategy relies on treatments with anticoagulants that unfortunately pose an inherent risk of bleeding complications. These anticoagulants primarily target clotting factors, often overlooking upstream events, including the release of neutrophil extracellular traps (NETs). Neutrophils are integral components of the innate immune system, traditionally known for their role in combating pathogens through NET formation. Emerging evidence has now revealed that NETs contribute to a prothrombotic milieu by promoting platelet activation, increasing thrombin generation, and providing a scaffold for clot formation. Additionally, NET components enhance clot stability and resistance to fibrinolysis. Clinical and preclinical studies have underscored the mechanistic involvement of NETs in the pathogenesis of thrombotic complications, since the clots obtained from patients and experimental models consistently exhibit the presence of NETs. Given these insights, the inhibition of NETs or NET formation is emerging as a promising therapeutic approach for ischemic thrombotic diseases. Recent investigations also implicate a role for the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome as a mediator of NETosis and thrombosis, suggesting that NLRP3 inhibition may also hold potential for mitigating thrombotic events. Therefore, future preclinical and clinical studies aimed at identifying and validating NLRP3 inhibition as a novel therapeutic intervention for thrombotic disorders are imperative.

Endpoints for clinical trials in ophthalmology

With the identification of novel targets, the number of interventional clinical trials in ophthalmology has increased. Visual acuity has for a long time been considered the gold standard endpoint for clinical trials, but in the recent years it became evident that other endpoints are required for many indications including geographic atrophy and inherited retinal disease. In glaucoma the currently available drugs were approved based on their IOP lowering capacity. Some recent findings do, however, indicate that at the same level of IOP reduction, not all drugs have the same effect on visual field progression. For neuroprotection trials in glaucoma, novel surrogate endpoints are required, which may either include functional or structural parameters or a combination of both. A number of potential surrogate endpoints for ophthalmology clinical trials have been identified, but their validation is complicated and requires solid scientific evidence. In this article we summarize candidates for clinical endpoints in ophthalmology with a focus on retinal disease and glaucoma. Functional and structural biomarkers, as well as quality of life measures are discussed, and their potential to serve as endpoints in pivotal trials is critically evaluated.

A retinal imaging system for combined measurement of optic nerve head vascular pulsation and stimulated vasodilation in humans

Vascular pulsation at the optic nerve head (ONH) reflects vessel properties. Reduction in the stimulated retinal vasodilatory capacity has been reported in diabetes, but its relation with vascular pulsation is unknown. Here we report a new retinal imaging system for correlative assessment of ONH vascular pulsation and stimulated retinal vasodilation. Retinal reflectance images were acquired before and during light flicker stimulation to quantify arterial and venous vasodilation (DAR, DVR) in subjects with and without diabetic retinopathy (N = 25). ONH vascular pulsation amplitude and frequency (PA, PF), were quantified by curve fitting of periodic intensity waveforms acquired in retinal vasculature (RV) and ONH tissue (ONHT) regions. The relationships between pulsation metrics, heart rate (HR), intraocular pressure (IOP), and vasodilatory responses were evaluated. Pulsation metrics were not significantly different between regions (p ≥ 0.70). In RV, inter-image variabilities of PA and PF were 10% and 6%, whereas inter-observer variabilities were 7% and 2% respectively. In both regions, PF was correlated with HR (p ≤ 0.001). PA was associated with DAR in both regions (p ≤ 0.03), but only with DVR in RV (p ≤ 0.05). Overall, ONH vascular pulsation was associated with stimulated retinal vasodilation, suggesting diabetes may have concomitant effects on retinal vasculature compliance and neurovascular coupling.

Autonomous Stabilization of Retinal Videos for Streamlining Assessment of Spontaneous Venous Pulsations

Spontaneous retinal Venous Pulsations (SVP) are rhythmic changes in the caliber of the central retinal vein and are observed in the optic disc region (ODR) of the retina. Its absence is a critical indicator of various ocular or neurological abnormalities. Recent advances in imaging technology have enabled the development of portable smartphone-based devices for observing the retina and assessment of SVPs. However, the quality of smartphone-based retinal videos is often poor due to noise and image jitting, which in return, can severely obstruct the observation of SVPs. In this work, we developed a fully automated retinal video stabilization method that enables the examination of SVPs captured by various mobile devices. Specifically, we first propose an ODR Spatio-Temporal Localization (ODR-STL) module to localize visible ODR and remove noisy and jittering frames. Then, we introduce a Noise-Aware Template Matching (NATM) module to stabilize high-quality video segments at a fixed position in the field of view. After the processing, the SVPs can be easily observed in the stabilized videos, significantly facilitating user observations. Furthermore, our method is cost-effective and has been tested in both subjective and objective evaluations. Both of the evaluations support its effectiveness in facilitating the observation of SVPs. This can improve the timely diagnosis and treatment of associated diseases, making it a valuable tool for eye health professionals.

Assessment of retinal vein pulsation through video-ophthalmoscopy and simultaneous biosignals acquisition

The phenomenon of retinal vein pulsation is still not a deeply understood topic in retinal hemodynamics. In this paper, we present a novel hardware solution for recording retinal video sequences and physiological signals using synchronized acquisition, we apply the photoplethysmographic principle for the semi-automatic processing of retinal video sequences and we analyse the timing of the vein collapse within the cardiac cycle using of an electrocardiographic signal (ECG). We measured the left eyes of healthy subjects and determined the phases of vein collapse within the cardiac cycle using a principle of photoplethysmography and a semi-automatic image processing approach. We found that the time to vein collapse (T_vc) is between 60 ms and 220 ms after the R-wave of the ECG signal, which corresponds to 6% to 28% of the cardiac cycle. We found no correlation between T_vc and the duration of the cardiac cycle and only a weak correlation between T_vc and age (0.37, p = 0.20), and T_vc and systolic blood pressure (-0.33, p = 0.25). The Tvc values are comparable to those of previously published papers and can contribute to the studies that analyze vein pulsations.

Retinal Vessel Pulsatile Characteristics Associated With Vascular Stiffness Can Predict the Rate of Functional Progression in Glaucoma Suspects

Purpose

Tissue stiffening and alterations in retinal blood flow have both been suggested as causative mechanisms of glaucomatous damage. We tested the hypothesis that retinal blood vessels also stiffen, using laser speckle flowgraphy (LSFG) to characterize vascular resistance.

Methods

In the longitudinal Portland Progression Project, 231 eyes of 124 subjects received LSFG scans of the optic nerve head (ONH) and automated perimetry every 6 months for six visits. Eyes were classified as either "glaucoma suspect" or "glaucoma" eyes based on the presence of functional loss on the first visit. Vascular resistance was quantified using the mean values of several instrument-defined parameterizations of the pulsatile waveform measured by LSFG, either in major vessels within the ONH (serving the retina) or in capillaries within ONH tissue, and age-adjusted using a separate group of 127 healthy eyes of 63 individuals. Parameters were compared against the severity and rate of change of functional loss using mean deviation (MD) over the six visits, within the two groups.

Results

Among 118 "glaucoma suspect" eyes (average MD, -0.4 dB; rate, -0.45 dB/y), higher vascular resistance was related to faster functional loss, but not current severity of loss. Parameters measured in major vessels were stronger predictors of rate than parameters measured in tissue. Among 113 "glaucoma" eyes (average MD, -4.3 dB; rate, -0.53 dB/y), higher vascular resistance was related to more severe current loss but not rate of loss.

Conclusions

Higher retinal vascular resistance and, by likely implication, stiffer retinal vessels were associated with more rapid functional loss in eyes without significant existing loss at baseline.

Empirical retinal venous pulse wave velocity using modified photoplethysmography

OBJECTIVE

Using the novel imaging method of high-speed modified photoplethysmography we measured the retinal venous pulse wave velocity in a single case.

RESULTS

A healthy 30-year-old subject underwent high-speed modified photoplethysmography (120 frames per second) with simultaneous ophthalmodynamometry at 26 Meditron units. A video of the optic nerve was analyzed using custom software. A harmonic regression model was fitted to each pixel in the time series and used to quantify the retinal vascular pulse wave parameters. Retinal venous pulsation at the optic disc was observed as a complex dynamic wall motion, whereas contraction commenced at a point in the vein at the center of the optic disc, and progressed centrifugally. The empirically estimated retinal venous pulse wave velocity at this segment was approximately 22.24694 mm/s. This measurement provides an estimate for future studies in the field.

Smartphone Ocular Fundal Photography in the Diagnosis of Raised Intracranial Pressure: A Novel Adaptation to Neurosurgical Practice

Background Consistently raised intracranial pressure (ICP) is a common final pathway to morbidity/mortality in many neurosurgical conditions. This underscores the need for early diagnosis and prompt management of raised ICP. This study aims to determine whether smartphone fundal photography features of raised ICP can accurately predict the computed tomography (CT) findings suggestive of elevated ICP in neurosurgery patients. Methods Dilated ocular fundal photography examinations using an ophthalmoscope adapter mounted on a smartphone were done on 82 patients with clinical suspicion of raised ICP. Fundal photography findings were recorded as pictures/videos for disc analysis. Patients subsequently had neuroimaging with results analyzed for radiological features of raised ICP. These were correlated with fundal photography findings. Results A total of 82 adult patients participated in this study. Chi-square analysis showed a relationship between radiological signs of raised ICP and the absence of spontaneous retinal venous pulsation (SRVP) (p=0.001). There was no relationship observed between papilledema and radiological signs of raised ICP. However, when the fundal photography signs were aggregated, there was a significant relationship between the fundal signs of raised ICP and radiological signs of raised ICP (p=0.004). The sensitivity and specificity of smartphone-fundoscopy-detected papilledema in predicting radiological signs of raised ICP were 43.2% and 100%, respectively, while those of absent SRVP were 100% and 92.6%, respectively. Conclusion Smartphone ophthalmoscopy is a reliable screening tool for evaluating ICP in neurosurgical patients. It should be introduced into the neurosurgeon's tools for prompt evaluation of raised ICP, especially in developing/resource-poor settings where CT or magnetic resonance imaging is not readily available.

Correlation between retinal vein pulse amplitude, estimated intracranial pressure, and postural change

Spaceflight associated neuro-ocular syndrome (SANS) is common amongst astronauts on long duration space missions and is associated with signs consistent with elevated cerebrospinal fluid (CSF) pressure. Additionally, CSF pressure has been found to be elevated in a significant proportion of astronauts in whom lumbar puncture was performed after successful mission completion. We have developed a retinal photoplethysmographic technique to measure retinal vein pulsation amplitudes. This technique has enabled the development of a non-invasive CSF pressure measurement apparatus. We tested the system on healthy volunteers in the sitting and supine posture to mimic the range of tilt table extremes and estimated the induced CSF pressure change using measurements from the CSF hydrostatic indifferent point. We found a significant relationship between pulsation amplitude change and estimated CSF pressure change (p < 0.0001) across a range from 2.7 to 7.1 mmHg. The increase in pulse amplitude was highest in the sitting posture with greater estimated CSF pressure increase (p < 0.0001), in keeping with physiologically predicted CSF pressure response. This technique may be useful for non-invasive measurement of CSF pressure fluctuations during long-term space voyages.

Non-Invasive Intracranial Pressure Monitoring

(1) Background: Intracranial pressure (ICP) monitoring plays a key role in the treatment of patients in intensive care units, as well as during long-term surgeries and interventions. The gold standard is invasive measurement and monitoring via ventricular drainage or a parenchymal probe. In recent decades, numerous methods for non-invasive measurement have been evaluated but none have become established in routine clinical practice. The aim of this study was to reflect on the current state of research and shed light on relevant techniques for future clinical application. (2) Methods: We performed a PubMed search for “non-invasive AND ICP AND (measurement OR monitoring)” and identified 306 results. On the basis of these search results, we conducted an in-depth source analysis to identify additional methods. Studies were analyzed for design, patient type (e.g., infants, adults, and shunt patients), statistical evaluation (correlation, accuracy, and reliability), number of included measurements, and statistical assessment of accuracy and reliability. (3) Results: MRI-ICP and two-depth Doppler showed the most potential (and were the most complex methods). Tympanic membrane temperature, diffuse correlation spectroscopy, natural resonance frequency, and retinal vein approaches were also promising. (4) Conclusions: To date, no convincing evidence supports the use of a particular method for non-invasive intracranial pressure measurement. However, many new approaches are under development.

Vessel Pulse Amplitude Mapping in Eyes With Central and Hemi Retinal Venous Occlusion

Purpose

The purpose of this study was to describe vessel pulse amplitude characteristics in eyes with central retinal vein occlusion (CRVO), hemiretinal vein occlusion (HVO), normal eyes (N1 N1), and the unaffected contralateral eyes of CRVO and HVO eyes (N1 CRVO and N1 HVO), as well as the unaffected hemivessels of HVO eyes (N2 HVO).

Methods

Ophthalmodynamometry estimates of blood column pulse amplitudes with modified photoplethysmography were timed against cardiac cycles. Harmonic analysis was performed on the vessel reflectance within 0.25 to 1 mm from the disc center to construct pulse amplitude maps. Linear mixed modeling was used to examine variable effects upon the log harmonic pulse amplitude.

Results

One hundred seven eyes were examined. Normal eyes had the highest mean venous pulse amplitude (2.08 ± 0.48 log u). CRVO had the lowest (0.99 ± 0.45 log u, P < 0.0001), followed by HVO (1.23 ± 0.46 log u, P = 0.0002) and N2 HVO (1.30 ± 0.59 log u, P = 0.0005). N1 CRVO (1.76 ± 0.34 log u, P = 0.52) and N1 HVO (1.33 ± 0.37 log u, P = 0.0101) had no significantly different mean amplitudes compared to N1 N1. Arterial amplitudes were lower than venous (P < 0.01) and reduced with venous occlusion (P < 0.01). Pulse amplitude versus amplitude over distance decreased along the N1 N1 vessels, with increasing slopes observed with CRVO (P < 0.01).

Conclusions

Pulse amplitude reduction and attenuation characteristics of arteries and veins in venous occlusion can be measured and are consistent with reduced vessel wall compliance and pulse wave transmission.

Translational Relevance

Retinal vascular pulse amplitudes can be measured, revealing occlusion induced changes, suggesting a role in evaluating the severity and progression of venous occlusion.

MSGANet-RAV: A multiscale guided attention network for artery-vein segmentation and classification from optic disc and retinal images

BACKGROUND

Retinal and optic disc images are used to assess changes in the retinal vasculature. These can be changes associated with diseases such as diabetic retinopathy and glaucoma or induced using ophthalmodynamometry to measure arterial and venous pressure. Key steps toward automating the assessment of these changes are the segmentation and classification of the veins and arteries. However, such segmentation and classification are still required to be manually labelled by experts. Such automated labelling is challenging because of the complex morphology, anatomical variations, alterations due to disease and scarcity of labelled data for algorithm development. We present a deep machine learning solution called the multiscale guided attention network for retinal artery and vein segmentation and classification (MSGANet-RAV).

METHODS

MSGANet-RAV was developed and tested on 383 colour clinical optic disc images from LEI-CENTRAL, constructed in-house and 40 colour fundus images from the AV-DRIVE public dataset. The datasets have a mean optic disc occupancy per image of 60.6% and 2.18%, respectively. MSGANet-RAV is a U-shaped encoder-decoder network, where the encoder extracts multiscale features, and the decoder includes a sequence of self-attention modules. The self-attention modules explore, guide and incorporate vessel-specific structural and contextual feature information to segment and classify central optic disc and retinal vessel pixels.

RESULTS

MSGANet-RAV achieved a pixel classification accuracy of 93.15%, sensitivity of 92.19%, and specificity of 94.13% on LEI-CENTRAL, outperforming several reference models. It similarly performed highly on AV-DRIVE with an accuracy, sensitivity and specificity of 95.48%, 93.59% and 97.27%, respectively.

CONCLUSION

The results show the efficacy of MSGANet-RAV for identifying central optic disc and retinal arteries and veins. The method can be used in automated systems designed to assess vascular changes in retinal and optic disc images quantitatively.

A machine learning approach in the non-invasive prediction of intracranial pressure using Modified Photoplethysmography

The ideal Intracranial pressure (ICP) estimation method should be accurate, reliable, cost-effective, compact, and associated with minimal morbidity/mortality. To this end several described non-invasive methods in ICP estimation have yielded promising results, however the reliability of these techniques have yet to supersede invasive methods of ICP measurement. Over several publications, we described a novel imaging method of Modified Photoplethysmography in the evaluation of the retinal vascular pulse parameters decomposed in the Fourier domain, which enables computationally efficient information filtering of the retinal vascular pulse wave. We applied this method in a population of 21 subjects undergoing lumbar puncture manometry. A regression model was derived by applying an Extreme Gradient Boost (XGB) machine learning algorithm using retinal vascular pulse harmonic regression waveform amplitude (HRWa), first and second harmonic cosine and sine coefficients (an1,2, bn1,2) among other features. Gain and SHapley Additive exPlanation (SHAP) values ranked feature importance in the model. Agreement between the predicted ICP mean, median and peak density with measured ICP was assessed using Bland-Altman bias±standard error. Feature gain of intraocular pressure (IOPi) (arterial = 0.6092, venous = 0.5476), and of the Fourier coefficients, an1 (arterial = 0.1000, venous = 0.1024) ranked highest in the XGB model for both vascular systems. The arterial model SHAP values demonstrated the importance of the laterality of the tested eye (1.2477), which was less prominent in the venous model (0.8710). External validation was achieved using seven hold-out test cases, where the median venous predicted ICP showed better agreement with measured ICP. Although the Bland-Altman bias from the venous model (0.034±1.8013 cm water (p<0.99)) was lower compared to that of the arterial model (0.139±1.6545 cm water (p<0.94)), the arterial model provided a potential avenue for internal validation of the prediction. This approach can potentially be integrated into a neurological clinical decision algorithm to evaluate the indication for lumbar puncture.

Near infra-red reflectance videography in the evaluation of retinal artery macroaneurysm pulsatility

Purpose

To describe pulsations of the retinal arteries detected in the course of evaluation of an exudative non-pulsatile retinal arterial macroaneurysm using near infra-red reflectance videography.

Observations

A 68-year-old patient underwent slit lamp examination, color retinal imaging, optical coherence tomography, fluorescein videography, short wave-length and near infrared fundus autofluorescence of the left, and near infrared reflectance videography of both eyes. A 1309.3 × 955.1 μm exudative lesion with intraretinal hemorrhage and retinal edema secondary to a retinal arterial macroaneurysm was observed along the superior temporal arcade between the retinal artery and vein. Bilateral serpentine and expansile spontaneous retinal artery pulsations were detected along the retinal vascular tree and imaged using near infrared reflectance videography. Fluorescein video-angiography showed an irregular filling defect of the lesion with minimal angiographic leakage. Whereas pulsations of the retinal arteries were visualized, no pulsations of the retinal arterial macroaneurysm were detected with either dynamic imaging modality, therefore observation was recommended. Significant spontaneous lesion regression was observed at one month follow-up.

Conclusionand Importance

Detection of spontaneous retinal artery pulsation and the assessment of exudative maculopathy due to an underlying retinal arterial macroaneurysm could be facilitated by near infrared reflectance videography. This imaging modality can aid in clinical decision-making where a non-pulsatile macroaneurysm would favor conservative management.

A review of risk factors for retinal vein occlusions

INTRODUCTION

Risk factors for retinal vein occlusion have been extensively studied, with varying population sizes. Smaller populations result in less certain measures of associations. The present review included studies with a relevant population size to identify clinically relevant risk factors for retinal vein occlusion. Understanding the risk factors of retinal vein occlusion is important for the management of these patients.

AREAS COVERED

A comprehensive literature review was conducted through a systematic literature search in PubMed and Embase. Additional studies were selected from cross references in the assessed studies. Weighted effect measures were calculated for all included risk factors.Risk factors associated with retinal vein occlusion included cardiovascular diseases, eye diseases, systemic diseases, medical interventions, and sociodemographic factors.

EXPERT OPINION

This review provided an extensive overview of a wide variety of risk factors increasing the risk of developing retinal vein occlusion. The severity of the identified risk factors indicated that these patients have been in contact with the health care system before their retinal vein occlusion event. Therefore, the clinical course for patients with retinal vein occlusion may benefit from a multidisciplinary collaboration between ophthalmologists and especially cardiologists.

A Review of the Methods of Non-Invasive Assessment of Intracranial Pressure through Ocular Measurement

The monitoring of intracranial pressure (ICP) is essential for the detection and treatment of most craniocerebral diseases. Invasive methods are the most accurate approach to measure ICP; however, these methods are prone to complications and have a limited range of applications. Therefore, non-invasive ICP measurement is preferable in a range of scenarios. The current non-invasive ICP measurement methods comprise fluid dynamics, and ophthalmic, otic, electrophysiological, and other methods. This article reviews eight methods of non-invasive estimation of ICP from ocular measurements, namely optic nerve sheath diameter, flash visual evoked potentials, two-depth transorbital Doppler ultrasonography, central retinal venous pressure, optical coherence tomography, pupillometry, intraocular pressure measurement, and retinal arteriole and venule diameter ratio. We evaluated and presented the indications and main advantages and disadvantages of these methods. Although these methods cannot completely replace invasive measurement, for some specific situations and patients, non-invasive measurement of ICP still has great potential.

Linear interactions between intraocular, intracranial pressure, and retinal vascular pulse amplitude in the fourier domain

Purpose

To compare the retinal vascular pulsatile characteristics in subjects with normal (ICP_n) and high (ICP_h) intracranial pressure and quantify the interactions between intraocular pressure, intracranial pressure, and retinal vascular pulse amplitude in the Fourier domain.

Materials and methods

Twenty-one subjects were examined using modified photoplethysmography with simultaneous ophthalmodynamometry. A harmonic regression model was fitted to each pixel in the time-series, and used to quantify the retinal vascular pulse wave parameters including the harmonic regression wave amplitude (HRW_a). The pulse wave attenuation was measured under different ranges of induced intraocular pressure (IOP_i), as a function of distance along the vessel (V_Dist). Intracranial pressure (ICP) was measured using lumbar puncture. A linear mixed-effects model was used to estimate the correlations between the Yeo-Johnson transformed harmonic regression wave amplitude (HRW_a-YJt) with the predictors (IOP_i, V_Dist and ICP). A comparison of the model coefficients was done by calculating the weighted Beta (β_x) coefficients.

Results

The median HRW_a in the ICP_n group was higher in the retinal veins (4.563, interquartile range (IQR) = 3.656) compared to the retinal arteries (3.475, IQR = 2.458), p<0.0001. In contrast, the ICP_h group demonstrated a reduction in the median venous HRW_a (3.655, IQR = 3.223) and an elevation in the median arterial HRW_a (3.616, IQR = 2.715), p<0.0001. Interactions of the pulsation amplitude with ICP showed a significant disordinal interaction and the loss of a main effect of the Fourier sine coefficient (b_n1) in the ICP_h group, suggesting that this coefficient reflects the retinal vascular response to ICP wave. The linear mixed-effects model (LME) showed the decay in the venous (HRW_a-YJt) was almost twice that in the retinal arteries (−0.067±0.002 compared to −0.028±0.0021 respectively, p<0.00001). The overall interaction models had a total explanatory power of (conditional R²) 38.7%, and 42% of which the fixed effects explained 8.8%, and 5.8% of the variance (marginal R²) for the venous and arterial models respectively. A comparison of the damping effect of V_Dist and ICP showed that ICP had less influence on pulse decay than distance in the retinal arteries (β_ICP = -0.21, se = ±0.017 compared to βVDist=-0.26, se = ±0.019), whereas the mean value was equal for the retinal veins (venous βVDist=-0.42, se = ±0.015, β_ICP = -0.42, se = ±0.019).

Conclusion

The retinal vascular pulsation characteristics in the ICP_h group showed high retinal arterial and low venous pulsation amplitudes. Interactions between retinal vascular pulsation amplitude and ICP suggest that the Fourier sine coefficient b_n1 reflects the retinal vascular response to the ICP wave. Although a matrix of regression lines showed high linear characteristics, the low model explanatory power precludes its use as a predictor of ICP. These results may guide future predictive modelling in non-invasive estimation of ICP using modified photoplethysmography.

Zero retinal vein pulsation amplitude extrapolated model in non-invasive intracranial pressure estimation

Intracranial pressure (ICP) includes the brain, optic nerve, and spinal cord pressures; it influences blood flow to those structures. Pathological elevation in ICP results in structural damage through various mechanisms, which adversely affects outcomes in traumatic brain injury and stroke. Currently, invasive procedures which tap directly into the cerebrospinal fluid are required to measure this pressure. Recent fluidic engineering modelling analogous to the ocular vascular flow suggests that retinal venous pulse amplitudes are predictably influenced by downstream pressures, suggesting that ICP could be estimated by analysing this pulse signal. We used this modelling theory and our photoplethysmographic (PPG) retinal venous pulse amplitude measurement system to measure amplitudes in 30 subjects undergoing invasive ICP measurements by lumbar puncture (LP) or external ventricular drain (EVD). We estimated ICP from these amplitudes using this modelling and found it to be accurate with a mean absolute error of 3.0 mmHg and a slope of 1.00 (r = 0.91). Ninety-four percent of differences between the PPG and invasive method were between − 5.5 and + 4.0 mmHg, which compares favourably to comparisons between LP and EVD. This type of modelling may be useful for understanding retinal vessel pulsatile fluid dynamics and may provide a method for non-invasive ICP measurement.

Modulation of Human Intraocular Pressure Using a Pneumatic System

Purpose

To technically validate a novel pneumatically based system and method for modulation of intraocular pressure (IOP) and to test its application in the human eye. Special attention was paid to the applicability of the pneumatically driven balloon, which realizes the modulation of the IOP through its contact with the conjunctiva.

Methods

A force sensor as key component of a customized measurement setup was used to check the applied pressure through the balloon. The IOP of 10 healthy subjects (4 female, 6 male, aged 28.8 ± 6.64 years) was modulated and increased linearly to at least 40 mmHg. At this point, the pressure inside the balloon was kept constant for 2 minutes, with IOP measurements taken every 40 seconds using a rebound tonometer.

Results

The technical setup led to an IOP decrease of 0.71 mmHg within 2 minutes at an operating point of 40 mmHg. For all subjects, the IOP could be increased up to 42.8 ± 3.6 mmHg, whereby a mean pressure decrease of 2.4 mmHg/min was determined, which seems to be caused mainly by physiological processes.

Conclusions

With the new pneumatically based setup, a targeted modulation in terms of level and constancy of the IOP can be realized.

Translational Relevance

Additional and, compared with the technique according to Löw, a more precise and more constant methodology for the modulation of the IOP, can significantly simplify the determination of retinal vessel pressures for clinical application. It is suitable for practical questions concerning an enhanced retinal venous pressure.

Retinal Vein Changes as a Biomarker to Guide Diagnosis and Management of Elevated Intracranial Pressure

Retinal vein changes, which can be observed on clinical exam or ophthalmic imaging, are promising non-invasive biomarkers for elevated intracranial pressure (ICP) as a complement to other markers of high ICP including optic nerve head swelling. Animal and human studies have demonstrated increase in retinal vein pressure associated with elevated ICP mediated by increase in cerebral venous pressure, compression of venous outflow by elevated cerebral spinal fluid pressure in the optic nerve sheath, and compression of venous outflow by optic nerve head swelling. Retinal vein pressure can be estimated using ophthalmodynamometry. Correlates of retinal vein pressure include spontaneous retinal venous pulsations, retinal vein diameter, and retinal vein tortuosity. All of these have potential for clinical use to diagnose and monitor elevated ICP. Challenges include diagnostic prediction based on single clinical measurements and accurate assessment of retinal vein parameters in cases where optic nerve head swelling limits visualization of the retinal veins.

Retinal arterial pulsation as an indicator of raised intraocular pressure

Ophthalmic emergencies are invariably challenging for the non-specialist to identify and evaluate, and may be complicated by occult but vision threatening raised intraocular pressure. We present a case of hypertensive uveitis accompanied by the finding of retinal arterial pulsation, which when visualised by direct ophthalmoscopy allows the non-specialist to identify significantly raised intraocular pressure requiring urgent evaluation by an ophthalmologist.

Measurement of the retinal venous pressure with a new instrument in healthy subjects

Background

The retinal venous pressure (RVP) is a determining factor for the blood supply of the retina as well as the optic nerve head and until recently has been measured by contact lens dynamometry (CLD). A new method has been developed, potentially offering better acceptance. The applicability and the results of both methods were compared.

Methods

The type of this study is cross sectional. The subjects were 36 healthy volunteers, age 26 ± 5 years (mean ± s). Tonometry: rebound tonometer (RT) (iCare). The measurements were performed during an increase in airway pressure of 20 mmHg (Valsalva manoeuvre). Principle of RVP measurement: the central retinal vein (CRV) is observed during an increase of intraocular pressure (IOP) and at the start of pulsation, which corresponds with the RVP. Two different instruments for the IOP enhancement where used: contact lens dynamometry and the new instrument, IOPstim. Principle: a deflated balloon of 8 mm diameter—placed on the sclera laterally of the cornea—is filled with air. As soon as a venous pulsation occurs, filling is stopped and the IOP is measured, equalling the RVP. Examination procedure: randomization of the sequence: CLD or IOPstim, IOP, mydriasis, IOP three single measurements (SM) of the IOP with RT or of the pressure increase with CLD at an airway pressure of 20 mmHg, 5 min break, IOP, and three SM using the second method at equal pressure (20 mmHg).

Results

Spontaneous pulsation of the CRV was present in all 36 subjects. Pressures are given in mmHg. IOP in mydriasis 15.6 ± 3.3 (m ± s). Median RVP (MRVP)) of the three SM: CLD/IOPstim, 37.7 ± 5.2/24.7 ± 4.8 (t test: p < 0.001). Range of SM: 3.2 ± 1.8/2.9 ± 1.3 (t test: p = 0.36). Intraclass correlation coefficient (ICC) of SM: 0.88/0.83. ANOVA in SM: p = 0.48/0.08. MRVP CLD minus MRVP IOPstim: 13.0 ± 5.6. Ratio MRVP CLD/MRVP IOPstim: 1.56 ± 3.1. Cooperation and agreeability were slightly better with the IOPstim.

Conclusion

This first study with the IOPstim in humans was deliberately performed in healthy volunteers using Valsalva conditions. As demonstrated by ICC and ANOVA, reproducible SM can be obtained by both methods and the range of the SM does not differ greatly. The higher MRVP in CLD could be explained by the different directions of the force vectors.

Ophthalmic Artery and Superior Ophthalmic Vein Blood Flow Dynamics in Glaucoma Investigated by Phase Contrast Magnetic Resonance Imaging

PRECIS

Ophthalmic artery (OA) and superior ophthalmic vein (SOV) blood flow were quantified by phase contrast magnetic resonance imaging (PC MRI) and seemed lower in glaucoma. Venous flow dynamics was different in glaucoma patients with a significantly decreased pulsatility.

INTRODUCTION

Studies using color Doppler imaging and optical coherence tomography flowmetry strongly suggested that vascular changes are involved in the pathophysiology of glaucoma, but the venous outflow has been little studied beyond the episcleral veins. This study measured the OA and the SOV flow by PC MRI in glaucoma patients compared with controls.

METHODS

Eleven primary open-angle glaucoma patients, with a mean±SD visual field deficit of -2.3±2.7 dB and retinal nerve fiber layer thickness of 92±13 µ, and 10 controls of similar age, were examined by PC MRI. The mean, maximal and minimal flow over cardiac cycle were measured. The variation of flow (ΔQ) was calculated.

RESULTS

The OA mean±SD mean flow was 13.21±6.79 in patients and 15.09±7.62 mL/min in controls (P=0.35) and the OA maximal flow was 25.70±12.08 mL/min in patients, and 28.45±10.64 mL/min in controls (P=0.22). In the SOV the mean±SD mean flow was 6.46±5.50 mL/min in patients and 7.21±6.04 mL/min in controls (P=0.81) and the maximal flow was 9.06±6.67 in patients versus 11.96±9.29 mL/min in controls (P=0.47). The ΔQ in the SOV was significantly lower in patients (5.45±2.54 mL/min) than in controls (9.09±5.74 mL/min) (P=0.04).

DISCUSSION

Although no significant difference was found, the mean and maximal flow in the OA and SOV seemed lower in glaucoma patients than in controls. The SOV flow waveform might be affected in glaucoma, corroborating the hypothesis of an impairment of venous outflow in those patients.

The association between circulating neutrophil extracellular trap related biomarkers and retinal vein occlusion incidence: A case-control pilot study

Retinal vein occlusion (RVO) is the second most common retinal vascular disorders and causes visual damage in a large population. Neutrophil extracellular traps (NETs) formation (NETosis) is an important cause of vascular diseases, however, the association between NETs related biomarkers and RVO development remained unclear. In this pilot study, a total of 77 RVO cases and 48 controls were included between Jan 2020 and July 2020. Besides, the circulating levels of three NETs related markers, cell-free DNA (cfDNA), myeloperoxidase (MPO)-DNA and citrullinated histone H3 (H3Cit), were detected in all the participants and thus the association between NETosis and RVO incidence was analyzed. Advanced assays were conducted to investigate the inflammation and thrombosis related biomarkers in RVO cases with higher or lower NETs biomarkers. When the results were considered, it was found that NETs biomarkers, including cfDNA, MPO-DNA and H3Cit, were increased in the RVO cases comparing with the controls (P < 0.05). Through the receiver operating characteristic (ROC) analyses, we found that circulating NETs related biomarkers demonstrated potential diagnostic effects for RVO and the AUCs of plasma cfDNA, MPO-DNA and H3Cit were 0.859, 0.871 and 0.928, respectively (P < 0.001). Through analyzing the correlations between circulating NETs markers and RVO stages and durations, inflammatory markers as well as thrombotic indexes, it was found that NETs were related with the RVO subtypes, inflammatory status and thrombus formation. In conclusion, the plasma NETs remnants are significantly increased in RVO cases. Besides, advanced studies demonstrate that inflammation as well as thrombus formation might be involved in this association.

Aqueous outflow regulation - 21st century concepts

We propose an integrated model of aqueous outflow control that employs a pump-conduit system in this article. Our model exploits accepted physiologic regulatory mechanisms such as those of the arterial, venous, and lymphatic systems. Here, we also provide a framework for developing novel diagnostic and therapeutic strategies to improve glaucoma patient care. In the model, the trabecular meshwork distends and recoils in response to continuous physiologic IOP transients like the ocular pulse, blinking, and eye movement. The elasticity of the trabecular meshwork determines cyclic volume changes in Schlemm's canal (SC). Tube-like SC inlet valves provide aqueous entry into the canal, and outlet valve leaflets at collector channels control aqueous exit from SC. Connections between the pressure-sensing trabecular meshwork and the outlet valve leaflets dynamically control flow from SC. Normal function requires regulation of the trabecular meshwork properties that determine distention and recoil. The aqueous pump-conduit provides short-term pressure control by varying stroke volume in response to pressure changes. Modulating TM constituents that regulate stroke volume provides long-term control. The aqueous outflow pump fails in glaucoma due to the loss of trabecular tissue elastance, as well as alterations in ciliary body tension. These processes lead to SC wall apposition and loss of motion. Visible evidence of pump failure includes a lack of pulsatile aqueous discharge into aqueous veins and reduced ability to reflux blood into SC. These alterations in the functional properties are challenging to monitor clinically. Phase-sensitive OCT now permits noninvasive, quantitative measurement of pulse-dependent TM motion in humans. This proposed conceptual model and related techniques offer a novel framework for understanding mechanisms, improving management, and development of therapeutic options for glaucoma.

Association of Intracranial Pressure and Spontaneous Retinal Venous Pulsation

Importance

A convenient and reliable method for noninvasive intracranial pressure assessments is desirable to reduce the need for invasive procedures (eg, intracranial pressure monitoring and lumbar punctures) and allow clinicians to identify and treat patients with intracranial hypertension in a timely manner.

Objective

To determine whether infrared video assessment of spontaneous retinal venous pulsation is associated with intracranial pressure and is a valid tool to indicate the presence or absence of raised intracranial pressure in patients without papilledema.

Design, Setting, and Participants

A single-center prospective study was conducted at a tertiary referral center between January 2017 and May 2018. Patients consecutively admitted for clinically indicated elective 24-hour invasive intracranial pressure monitoring had ophthalmic review including infrared video recording of their spontaneous venous pulsation. Two neuro-ophthalmologists, who were masked to the intracranial pressure monitoring results, independently graded the spontaneous venous pulsation (grade 0 to 3). Analysis began in June 2018.

Main Outcomes and Measures

The association between simultaneously recorded intracranial pressure and spontaneous venous pulsation (binary variable: present/absent) assessed through retinal infrared video recordings was evaluated using a multiple linear regression model.

Results

Of 105 patients, the mean (SD) age was 39 (14) years, and 79 (75%) were women. The mean (SD) simultaneous intracranial pressure was 1 (5) mm Hg for 91 patients (86.7%) with spontaneous venous pulsations and 13 (14) mm Hg for 14 patients (13.3%) without spontaneous venous pulsations. A multiple linear regression model adjusted for 7 potential confounders confirmed a statistically significant association between intracranial pressure and spontaneous venous pulsation (β = -9.1; 95% CI, -13.7 to -4.6; P < .001; adjusted R2 = 0.42).

Conclusions and Relevance

The absence of spontaneous venous pulsation on retinal infrared video recordings is significantly associated with higher levels of intracranial pressure and should raise the suspicion of intracranial hypertension.

A combined convolutional and recurrent neural network for enhanced glaucoma detection

Glaucoma, a leading cause of blindness, is a multifaceted disease with several patho-physiological features manifesting in single fundus images (e.g., optic nerve cupping) as well as fundus videos (e.g., vascular pulsatility index). Current convolutional neural networks (CNNs) developed to detect glaucoma are all based on spatial features embedded in an image. We developed a combined CNN and recurrent neural network (RNN) that not only extracts the spatial features in a fundus image but also the temporal features embedded in a fundus video (i.e., sequential images). A total of 1810 fundus images and 295 fundus videos were used to train a CNN and a combined CNN and Long Short-Term Memory RNN. The combined CNN/RNN model reached an average F-measure of 96.2% in separating glaucoma from healthy eyes. In contrast, the base CNN model reached an average F-measure of only 79.2%. This proof-of-concept study demonstrates that extracting spatial and temporal features from fundus videos using a combined CNN and RNN, can markedly enhance the accuracy of glaucoma detection.

Retinal venous pressure is decreased after anti-VEGF therapy in patients with retinal vein occlusion-related macular edema

Purpose

The pathomechanism leading to retinal vein occlusion (RVO) is unclear. Mechanical compression, thrombosis, and functional contractions of veins are discussed as the reasons for the increased resistance of venous outflow. We evaluated changes in the retinal venous pressure (RVP) following intravitreal injection of anti-vascular endothelial growth factor (VEGF) agent to determine the effect on RVO-related macular edema.

Methods

Twenty-six patients with RVO-related macular edema (16 branch RVOs [BRVOs] and 10 central RVOs [CRVOs], age 72.5 ± 8.8 years) who visited our hospital were included in this prospective study. Visual acuity (VA), intraocular pressure (IOP), central retinal thickness (CRT) determined by macular optical coherence tomography, and RVP measured using an ophthalmodynamometer were obtained before intravitreal injection of ranibizumab (IVR) and 1 month later.

Results

Comparison of the BRVOs and CRVOs showed that VA was significantly improved by a single injection in BRVOs (P < 0.0001; P = 0.1087 for CRVOs), but CRT and RVP were significantly decreased without significant difference in IOP after the treatment in both groups (P < 0.0001).

Conclusion

The anti-VEGF treatment resulted in a significant decrease in the RVP, but the RVP remained significantly higher than the IOP. An increased RVP plays a decisive role in the formation of macula edema, and reducing it is desirable.

The Distribution of Retinal Venous Pressure and Intraocular Pressure Differs Significantly in Patients with Primary Open-Angle Glaucoma

INTRODUCTION

Until now, venous pressure within the eye has widely been equated with intraocular pressure (IOP). Measurements with dynamometers calibrated in instrument units or in force showed that the retinal venous pressure (RVP) may be higher than the IOP in glaucoma patients. In this study, the RVP was measured with a contact lens dynamometer calibrated in mmHg.

METHODS

Study type: cross-sectional.

SUBJECTS

Fifty consecutive patients with primary open-angle glaucoma (POAG) who underwent diurnal curve measurement under medication. Age: 69 ± 8 years. Measurement of RVP: contact lens dynamometry. IOP measurement: dynamic contour tonometry.

RESULTS

Pressures are given in mmHg. In all 50 patients, the IOP was 15.9 (13.6; 17.1) [median (Q1; Q3)], and the RVP was 17.4 (14.8; 27.2). The distribution of the IOP was normal and that of the RVP was right skewed. In the subgroup of 34 patients with spontaneous pulsation of the central retinal vein (SVP), the IOP and therefore, by definition, the RVP was 16.5 (13.7; 17.4). In the subgroup of 16 patients without SVP, the IOP was 14.8 (13.3; 16.4), and the RVP was 31.3 (26.2; 38.8) (p ≤ 0.001). In systemic treatment, the prescribed drugs were (the number of patients is given in parentheses): ACE inhibitors (20), β-blockers (17), angiotensin II-receptor blockers (13), calcium channel blockers (12), diuretics (7). No difference in RVP was observed between patients receiving these drugs and not receiving them, except in the β-blocker group. Here, the 17 patients with systemic β-blockers had a median RVP of 15.6 mmHg and without 20.2 mmHg (p = 0.003). In the 16 patients with a higher RVP than IOP, only one patient received a systemic β-blocker. The median IOP was 15.7 mmHg with systemic β-blockers and 16.1 mmHg without (p = 0.85).

CONCLUSION

In a subgroup of 16 of the 50 patients studied, the RVP was greater than the IOP by a highly statistically and clinically significant degree. According to the widely accepted thinking on the pathophysiology of retinal and optic nerve head circulation, the blood flow in these tissues may be much more compromised in this group of patients than has been assumed. They may be identified by a missing SVP. Topical and systemic medications showed no statistically significant influence on the RVP, except for the systemic β-blockers, in which the RVP was lower by 4.6 mmHg than for the patients who did not receive these drugs (p = 0.003).

Effect of Changing Heart Rate on the Ocular Pulse and Dynamic Biomechanical Behavior of the Optic Nerve Head

Purpose

To study the effect of changing heart rate on the ocular pulse and the dynamic biomechanical behavior of the optic nerve head (ONH) using a comprehensive mathematical model.

Methods

In a finite element model of a healthy eye, a biphasic choroid consisted of a solid phase with connective tissues and a fluid phase with blood, and the lamina cribrosa (LC) was viscoelastic as characterized by a stress-relaxation test. We applied arterial pressures at 18 ocular entry sites (posterior ciliary arteries), and venous pressures at four exit sites (vortex veins). In the model, the heart rate was varied from 60 to 120 bpm (increment: 20 bpm). We assessed the ocular pulse amplitude (OPA), pulse volume, ONH deformations, and the dynamic modulus of the LC at different heart rates.

Results

With an increasing heart rate, the OPA decreased by 0.04 mm Hg for every 10 bpm increase in heart rate. The ocular pulse volume decreased linearly by 0.13 µL for every 10 bpm increase in heart rate. The storage modulus and the loss modulus of the LC increased by 0.014 and 0.04 MPa, respectively, for every 10 bpm increase in heart rate.

Conclusions

In our model, the OPA, pulse volume, and ONH deformations decreased with an increasing heart rate, whereas the LC became stiffer. The effects of blood pressure/heart rate changes on ONH stiffening may be of interest for glaucoma pathology.

Morphometric, Hemodynamic, and Biomechanical Factors Influencing Blood Flow and Oxygen Concentration in the Human Lamina Cribrosa

Purpose

We developed a combined biomechanical and hemodynamic model of the human eye to estimate blood flow and oxygen concentration within the lamina cribrosa (LC) and rank the factors that influence LC oxygen concentration.

Methods

We generated 5000 finite-element eye models with detailed microcapillary networks of the LC and computed the oxygen concentration of the lamina retinal ganglion cell axons. For each model, we varied the intraocular pressure (IOP) from 10 mm Hg to 55 mm Hg in 5-mm Hg increments, the cerebrospinal fluid pressure (13 ± 2 mm Hg), cup depth (0.2 ± 0.1 mm), scleral stiffness (±20% of the mean values), LC stiffness (0.41 ± 0.2 MPa), LC radius (1.2 ± 0.12 mm), average LC pore size (5400 ± 2400 µm²), the microcapillary arrangement (radial, isotropic, or circumferential), and perfusion pressure (50 ± 9 mm Hg). Blood flow was assumed to originate from the LC periphery and drain via the central retinal vein. Finally, we performed linear regressions to rank the influence of each factor on the LC tissue oxygen concentration.

Results

LC radius and perfusion pressure were the most important factors in influencing the oxygen concentration of the LC. IOP was another important parameter, and eyes with higher IOP had higher compressive strain and slightly lower oxygen concentration. In general, superior–inferior regions of the LC had significantly lower oxygen concentration than the nasal–temporal regions, resulting in an hourglass pattern of oxygen deficiency.

Conclusions

To the best of our knowledge, this study is the first to implement a comprehensive hemodynamical model of the eye that accounts for the biomechanical forces and morphological parameters of the LC. The results provide further insight into the possible relationship of biomechanical and vascular pathways leading to ischemia-induced optic neuropathy.

Spontaneous Venous Pulsations Detected With Infrared Videography

BACKGROUND

Assessment of spontaneous venous pulsation (SVP) is commonly undertaken to help determine whether intracranial pressure (ICP) is elevated. Previous studies using direct ophthalmoscopy or slit-lamp assessments have found that SVP is not observed in 67%-81% of subjects with normal ICP, and that interobserver agreement when grading SVP is poor.

METHODS

Patients (n = 105) undergoing clinically indicated retinal OCT scans, who were all believed to have normal ICP, had 10-second infrared video recordings performed with the Heidelberg Spectralis OCT system (Heidelberg Engineering GmbH, Heidelberg, Germany). The presence and amplitude of SVP in each video was independently graded by 2 neuro-ophthalmologists.

RESULTS

The 2 observers found SVP present in 97% and 98% of right eyes and in one or both eyes in 99% and 100% of subjects. Interobserver agreement was high (Cohen's kappa 0.82 for right eyes). Optic discs with a smaller cup had a significantly lower SVP amplitude (Spearman's rho = 0.22, P = 0.02).

CONCLUSIONS

Infrared video is widely available in eye clinics by the use of OCT imaging systems and is substantially more sensitive in detecting SVP than traditional assessments using ophthalmoscopy. SVP is absent in as few as 1% of people with presumed normal ICP.

Measurement of normal retinal vascular pulse wave attenuation using modified photoplethysmography

Pulse wave attenuation characteristics reflect compliance and resistance properties of the vessel wall as well as initial pulse generation factors. Recently, it has become possible to measure and map the retinal vessel wall pulse wave amplitudes. Predictable pulse wave amplitude distribution may allow inferences to be made concerning vascular compliance and resistance. Twenty-eight eyes from sixteen subjects (8 male and 8 female) were examined using modified retinal photoplethysmography with simultaneous ophthalmodynamometry. This allowed the assessment of vessel wall pulsation amplitudes under a dynamic range of intraocular pressures. Pulse amplitudes were calculated using harmonic regression analysis. The pulse wave attenuation was measured under different ranges of ophthalmodynamometric force (ODF) as a function of distance along the vessel (VDist), which in turn was calculated in disc diameters (DD) from the center of the optic disc. A linear mixed-effects model with randomized slopes and intercepts was used to estimate the correlations between the logarithmically transformed harmonic regression wave amplitude (HRWa) and the Fourier trigonometric coefficients with the predictors (VDist and ODF). The retinal venous harmonic regression wave attenuation (coefficient value±standard error) -0.40±0.065/DD, (p-value < 0.00001, 95% confidence interval (CI) -0.53 to -0.27), which was approximately twice that of the arterial -0.17±0.048/DD, (p-value < 0.0004, 95% CI = -0.27 to -0.08). There was a positive correlation between attenuation of the harmonic regression wave and ophthalmodynamometric force in both vascular systems. The attenuation of all but the sine coefficient of the second Fourier harmonic (bn2) achieved statistical significance in the correlation with VDist. The cosine coefficient of the first Fourier harmonic an1 was the only coefficient to achieve statistical significance in the correlation with the predictors VDist and ODF in both vascular systems. The an1 coefficient value in the correlation with VDist was -3.79±0.78 and -1.269±0.37 (p < 0.0006), while this coefficient value in the correlation with ODF was 0.026±0.0099 and 0.009±0.04 (p < 0.01) in both the retinal veins and arteries respectively. The predictable attenuation characteristics in normal subjects suggest that this technique may allow the non-invasive quantification of retinal vascular compliance and other hemodynamic parameters.

The Detection of Spontaneous Venous Pulsation with Smartphone Video Ophthalmoscopy

Purpose

Spontaneous venous pulsation (SVP) has a high negative predictive value for raised intracranial pressure and is a useful sign when assessing patients with headache. The objective was to determine if smartphone-based video ophthalmoscopy can detect SVP.

Patients and Methods

In total 233 patients and 291 eyes were recruited from the Dunedin Hospital eye clinic from July to November 2018. Patients were examined by a clinician and graded for SVP with a slit lamp and 78 Dioptre lens. Videos were taken with a smartphone ophthalmoscope and graded by two separate clinicians blinded to the slit lamp findings.

Results

Only 272 eyes of 215 patients were included, as others failed in the inclusion criteria for overall video quality. Sensitivity was calculated as how likely the presence of SVP on video was indicative of the presence of SVP on slit lamp. Sensitivity was 84.77% for Observer 1, with 128 videos graded as positive for SVP on video ophthalmoscopy of the 151 identified as positive on slit lamp examination. Sensitivity was 76.82% for Observer 2 with 116 videos correctly identified. The false positive rate was calculated as the number of videos graded positive for SVP that had been graded as negative on slit lamp examination. This was 10.74% for observer 1 and 31.40% for observer 2.

Conclusion

This study demonstrates that SVP is detected by video ophthalmoscopy. This may be a useful triage, telemedicine and referral tool to be used for patients with headache in a primary care setting.

Ocular blood flow as a clinical observation: Value, limitations and data analysis

Alterations in ocular blood flow have been identified as important risk factors for the onset and progression of numerous diseases of the eye. In particular, several population-based and longitudinal-based studies have provided compelling evidence of hemodynamic biomarkers as independent risk factors for ocular disease throughout several different geographic regions. Despite this evidence, the relative contribution of blood flow to ocular physiology and pathology in synergy with other risk factors and comorbidities (e.g., age, gender, race, diabetes and hypertension) remains uncertain. There is currently no gold standard for assessing all relevant vascular beds in the eye, and the heterogeneous vascular biomarkers derived from multiple ocular imaging technologies are non-interchangeable and difficult to interpret as a whole. As a result of these disease complexities and imaging limitations, standard statistical methods often yield inconsistent results across studies and are unable to quantify or explain a patient's overall risk for ocular disease. Combining mathematical modeling with artificial intelligence holds great promise for advancing data analysis in ophthalmology and enabling individualized risk assessment from diverse, multi-input clinical and demographic biomarkers. Mechanism-driven mathematical modeling makes virtual laboratories available to investigate pathogenic mechanisms, advance diagnostic ability and improve disease management. Artificial intelligence provides a novel method for utilizing a vast amount of data from a wide range of patient types to diagnose and monitor ocular disease. This article reviews the state of the art and major unanswered questions related to ocular vascular anatomy and physiology, ocular imaging techniques, clinical findings in glaucoma and other eye diseases, and mechanistic modeling predictions, while laying a path for integrating clinical observations with mathematical models and artificial intelligence. Viable alternatives for integrated data analysis are proposed that aim to overcome the limitations of standard statistical approaches and enable individually tailored precision medicine in ophthalmology.

Waveform analysis of human retinal and choroidal blood flow with laser Doppler holography

Laser Doppler holography was introduced as a full-field imaging technique to measure blood flow in the retina and choroid with an as yet unrivaled temporal resolution. We here investigate separating the different contributions to the power Doppler signal in order to isolate the flow waveforms of vessels in the posterior pole of the human eye. Distinct flow behaviors are found in retinal arteries and veins with seemingly interrelated waveforms. We demonstrate a full field mapping of the local resistivity index, and the possibility to perform unambiguous identification of retinal arteries and veins on the basis of their systolodiastolic variations. Finally we investigate the arterial flow waveforms in the retina and choroid and find synchronous and similar waveforms, although with a lower pulsatility in choroidal arteries. This work demonstrates the potential held by laser Doppler holography to study ocular hemodynamics in healthy and diseased eyes.

Detection and characterization of tree shrew retinal venous pulsations: An animal model to study human retinal venous pulsations

Spontaneous retinal venous pulsations (SRVPs), pulsations of branches of the central retinal vein, are affected by intraocular pressure (IOP) and intracranial pressure (ICP) and thus convey potentially-useful information about ICP. However, the exact relationship between SRVPs, IOP, and ICP is unknown. It is not easily feasible to study this relationship in humans, necessitating the use of an animal model. We here propose tree shrews as a suitable animal model to study the complex relationship between SRVPs, IOP, and ICP. Tree shrew SRVP incidence was determined in a population of animals. Following validation of a modified IOP control system to accurately and quickly control IOP, IOP and/or ICP were manipulated in two tree shrews with SRVPs and the effects on SRVP properties were quantified. SRVPs were present in 75% of tree shrews at physiologic IOP and ICP. Altering IOP or ICP produced changes in tree shrew SRVP properties; specifically, increasing IOP caused SRVP amplitude to increase, while increasing ICP caused SRVP amplitude to decrease. In addition, a higher IOP was necessary to generate SRVPs at a higher ICP than at a lower ICP. SRVPs occur with a similar incidence in tree shrews as in humans, and tree shrew SRVPs are affected by changes in IOP and ICP in a manner qualitatively similar to that reported in humans. In view of anatomic similarities, tree shrews are a promising animal model system to further study the complex relationship between SRVPs, IOP, and ICP.

Estimation of Time Delay Between Artery and Vein Pulsation using Experimental Video-Ophthalmoscope

The fundus observation by ophthalmoscope is a non-invasive approach for diagnosis of various retinal diseases. The vein and artery pulsation are usually clearly apparent on fundus and might be also important for medical practice. Thus our method focuses on these changes and analyzes the time delay between the pulsation signal detected in the vein and the artery region. Data acquired by an experimental video-ophthalmoscope from five subjects with no eye diseases are analyzed. The analysis is based on the selection of artery and vein regions of interest and computation of averaged brightness within these regions for each frame. These extracted signals are filtered, interpolated and the trend is eliminated. Finally, the delays between artery and vein pulsation signals are determined using phase spectra. The measured delays are in the range of 15 to 95 ms, which is comparable with other published results.

Regulation of Choroidal Blood Flow During Isometric Exercise at Different Levels of Intraocular Pressure

Purpose

There is evidence that choroidal blood flow (ChBF) is regulated in a complex way during changes in ocular perfusion pressure (OPP). We hypothesized that ChBF regulates better in response to changes in mean arterial pressure (MAP) than in intraocular pressure (IOP).

Methods

Eighteen volunteers (mean age, 26 years) were recruited for a randomized, three-way crossover design. MAP was varied via isometric exercise. IOP was either kept normal or elevated by 10 or 20 mm Hg by using a suction cup. Subfoveal ChBF was measured continuously for 8 minutes with laser Doppler flowmetry and OPP was calculated as 2/3*MAP-IOP. For data analysis, values from all subjects were pooled according to either IOP or MAP values, and correlation analyses were done.

Results

When data were grouped according to IOP, no correlation was observed between ChBF and MAP, but ChBF was lower the higher the IOP (P < 0.001). When data were grouped according to MAP, a significant correlation was found between ChBF and IOP (P < 0.001). When data were pooled according to IOP, the correlation between ChBF and OPP was weaker (P < 0.05). The OPP at which ChBF significantly increased from baseline was 61.3% ± 4.9% without suction cup, 65.2% ± 3.5% when IOP was increased by 10 mm Hg, and slightly lower when IOP was increased by 20 mm Hg (56.3% ± 4.8%, P = 0.07), but this effect did not reach the level of significance.

Conclusions

The present study provides further evidence that the regulation of ChBF during changes in OPP is controlled by complex mechanisms in humans and has less capacity to adapt to IOP elevation than to MAP increase.

Investigating spontaneous retinal venous pulsation using Doppler optical coherence tomography

We demonstrate the advantages of optical coherence tomography (OCT) imaging for investigation of spontaneous retinal venous pulsation (SRVP). The pulsatile changes in venous vessel caliber are analyzed qualitatively and quantitatively using conventional intensity-based OCT as well as the functional extension Doppler OCT (DOCT). Single-channel and double-channel line scanning protocols of our multi-channel OCT prototype are employed to investigate venous pulsatile caliber oscillations as well as venous flow pulsatility in the eyes of healthy volunteers. A comparison to recordings of scanning laser ophthalmoscopy (SLO) – a standard en-face imaging modality for evaluation of SRVP – is provided, emphasizing the advantages of tomographic image acquisition. To the best of our knowledge, this is the first quantitative time-resolved investigation of SRVP and associated retinal perfusion characteristics using OCT.