Retinal Imaging for Neurological Diseases: "A Window into the Brain"

Computational single fundus image restoration techniques: a review

Fundus cameras are widely used by ophthalmologists for monitoring and diagnosing retinal pathologies. Unfortunately, no optical system is perfect, and the visibility of retinal images can be greatly degraded due to the presence of problematic illumination, intraocular scattering, or blurriness caused by sudden movements. To improve image quality, different retinal image restoration/enhancement techniques have been developed, which play an important role in improving the performance of various clinical and computer-assisted applications. This paper gives a comprehensive review of these restoration/enhancement techniques, discusses their underlying mathematical models, and shows how they may be effectively applied in real-life practice to increase the visual quality of retinal images for potential clinical applications including diagnosis and retinal structure recognition. All three main topics of retinal image restoration/enhancement techniques, i.e., illumination correction, dehazing, and deblurring, are addressed. Finally, some considerations about challenges and the future scope of retinal image restoration/enhancement techniques will be discussed.

The Eye as the Window to the Heart: Optical Coherence Tomography Angiography Biomarkers as Indicators of Cardiovascular Disease

Alterations in microvasculature represent some of the earliest pathological processes across a wide variety of human diseases. In many organs, however, inaccessibility and difficulty in directly imaging tissues prevent the assessment of microvascular changes, thereby significantly limiting their translation into improved patient care. The eye provides a unique solution by allowing for the non-invasive and direct visualization and quantification of many aspects of the human microvasculature, including biomarkers for structure, function, hemodynamics, and metabolism. Optical coherence tomography angiography (OCTA) studies have specifically identified reduced capillary densities at the level of the retina in several eye diseases including glaucoma. This narrative review examines the published data related to OCTA-assessed microvasculature biomarkers and major systemic cardiovascular disease. While loss of capillaries is being established in various ocular disease, pilot data suggest that changes in the retinal microvasculature, especially within the macula, may also reflect small vessel damage occurring in other organs resulting from cardiovascular disease. Current evidence suggests retinal microvascular biomarkers as potential indicators of major systemic cardiovascular diseases, including systemic arterial hypertension, atherosclerotic disease, and congestive heart failure.

Optical coherence tomography angiography measurements in Parkinson's disease: A systematic review and meta-analysis

Optical coherence tomography angiography (OCT-A) is an ocular imaging technology that has emerged as a non-invasive tool to evaluate retinal microvascular changes in neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease. While several studies have reported on the presence of pathologic retinal microvascular alterations in PD, the utility of OCT-A as a biomarker for PD evaluation is still unclear. A systematic review and meta-analysis were performed to explore the current evidence for the role of OCT-A in PD published up until June 2022. PubMed, Scopus, and Web of Science databases were used to systematically identify relevant papers and a meta-analysis was conducted using Stata16 software according to the level of heterogeneity applying a random- or fixed-effect model. Thirteen studies of 925 eyes in the PD group and 1501 eyes in the control group assessing OCT-A findings in PD patients were included. The meta-analyses revealed that the foveal region of PD patients had a significantly lower vessel density in the superficial capillary plexus (SCP) compared to healthy controls but that there were no significant differences in the foveal avascular zone, the SCP in whole, parafoveal, and perifoveal regions, and deep capillary plexus. OCT-A metrics may act as a potential biomarker for a more accurate and early PD diagnosis. Still, the OCT-A algorithms and interchangeability between OCT-A devices require further standardization to draw clinical conclusions regarding their utility.

MUTE: A multilevel-stimulated denoising strategy for single cataractous retinal image dehazing

In this research, we studied the duality between cataractous retinal image dehazing and image denoising and proposed that the dehazing task for cataractous retinal images can be achieved with the combination of image denoising and sigmoid function. To do so, we introduce the double-pass fundus reflection model in the YPbPr color space and developed a multilevel stimulated denoising strategy termed MUTE. The transmission matrix of the cataract layer is expressed as the superposition of denoised raw images of different levels weighted by pixel-wise sigmoid functions. We further designed an intensity-based cost function that can guide the updating of the model parameters. They are updated by gradient descent with adaptive momentum estimation, which gives us the final refined transmission matrix of the cataract layer. We tested our methods on cataract retinal images from both public and proprietary databases, and we compared the performance of our method with other state-of-the-art enhancement methods. Both visual assessments and objective assessments show the superiority of the proposed method. We further demonstrated three potential applications including blood vessel segmentation, retinal image registrations, and diagnosing with enhanced images that may largely benefit from our proposed methods.

Systemic Adverse Events Among Patients With Diabetes Treated With Intravitreal Anti-Vascular Endothelial Growth Factor Injections

Importance

Anti-vascular endothelial growth factor (VEGF) agents are currently the mainstay of treatment for diabetic retinopathy (DR). Although effective, data on their systemic safety remains inconclusive, particularly in high-risk patient groups.

Objective

To explore the systemic safety of intravitreal anti-VEGF agents among patients with diabetes.

Design, Setting, and Participants

This was a retrospective, longitudinal population-based analysis of the Corporate Data Warehouse, a large-scale database of patients within the US Veteran Health Affairs. All patients 18 years and older with type 2 diabetes who were seen at any Veterans Affairs health care facility in the US between January 1, 2011, and December 31, 2012, were identified. Data were then extracted on incident systemic adverse events among this patient cohort from January 1, 2013, to December 31, 2017. All individuals with diabetes who did and did not receive anti-VEGF injections were included. Patients with a history of prior systemic adverse events and those who received an intravitreal injection between January 1, 2011, and December 31, 2012, were excluded. Data were analyzed from October 2019 to March 2023.

Exposure

Anti-VEGF injection.

Main Outcomes and Measures

Proportion of patients with any incident systemic adverse event, acute myocardial infarction, cardiovascular disease, or kidney disease at 1-, 3-, and 5-year follow-up.

Results

A total of 1 731 782 patients (mean [SD] age, 63.8 [12.3] years; 1 656 589 [95.7%] male) with type 2 diabetes were included. DR was present in 476 013 (27.5%), and 14 022 (0.8%) received anti-VEGF injections. Of the total number of patients with type 2 diabetes, 321 940 (18.6%) developed systemic adverse events between 2013 and 2017. The 5-year cumulative incidence of any systemic adverse event was 37.0% (5187/14 022) in the injection group vs 18.4% (316 753/1 717 760) in the noninjection group (P < .001). Anti-VEGF injections were independently associated with a higher likelihood of developing any systemic adverse event (odds ratio, 1.8; 95% CI, 1.7-1.9) when controlling for age, race, sex, ethnicity, tobacco use, severity of DR, Deyo-Charlson Comorbidity Index score, mean hemoglobin A1c, total number of injections, and statin use.

Conclusion and Relevance

In this study, intravitreal anti-VEGF injections were independently associated with a higher likelihood of systemic adverse events among patients with diabetes.

A systematic survey of advances in retinal imaging modalities for Alzheimer's disease diagnosis

Recent advances in retinal imaging pathophysiology have shown a new function for biomarkers in Alzheimer's disease diagnosis and prognosis. The significant improvements in Optical coherence tomography (OCT) retinal imaging have led to significant clinical translation, particularly in Alzheimer's disease detection. This systematic review will provide a comprehensive overview of retinal imaging in clinical applications, with a special focus on biomarker analysis for use in Alzheimer's disease detection. Articles on OCT retinal imaging in Alzheimer's disease diagnosis were identified in PubMed, Google Scholar, IEEE Xplore, and Research Gate databases until March 2021. Those studies using simultaneous retinal imaging acquisition were chosen, while those using sequential techniques were rejected. "Alzheimer's disease" and "Dementia" were searched alone and in combination with "OCT" and "retinal imaging". Approximately 1000 publications were searched, and after deleting duplicate articles, 145 relevant studies focused on the diagnosis of Alzheimer's disease utilizing retinal imaging were chosen for study. OCT has recently been demonstrated to be a valuable technique in clinical practice as according to this survey, 57% of the researchers employed optical coherence tomography, 19% used ocular fundus imaging, 13% used scanning laser ophthalmoscopy, and 11% have used multimodal imaging to diagnose Alzheimer disease. Retinal imaging has become an important diagnostic technique for Alzheimer's disease. Given the scarcity of available literature, it is clear that future prospective trials involving larger and more homogeneous groups are necessary, and the work can be expanded by evaluating its significance utilizing a machine-learning platform rather than simply using statistical methodologies.

Towards Stroke Biomarkers on Fundus Retinal Imaging: A Comparison Between Vasculature Embeddings and General Purpose Convolutional Neural Networks

Fundus Retinal imaging is an easy-to-acquire modality typically used for monitoring eye health. Current evidence indicates that the retina, and its vasculature in particular, is associated with other disease processes making it an ideal candidate for biomarker discovery. The development of these biomarkers has typically relied on predefined measurements, which makes the development process slow. Recently, representation learning algorithms such as general purpose convolutional neural networks or vasculature embeddings have been proposed as an approach to learn imaging biomarkers directly from the data, hence greatly speeding up their discovery. In this work, we compare and contrast different state-of-the-art retina biomarker discovery methods to identify signs of past stroke in the retinas of a curated patient cohort of 2,472 subjects from the UK Biobank dataset. We investigate two convolutional neural networks previously used in retina biomarker discovery and directly trained on the stroke outcome, and an extension of the vasculature embedding approach which infers its feature representation from the vasculature and combines the information of retinal images from both eyes.In our experiments, we show that the pipeline based on vasculature embeddings has comparable or better performance than other methods with a much more compact feature representation and ease of training.Clinical Relevance-This study compares and contrasts three retinal biomarker discovery strategies, using a curated dataset of subject evidence, for the analysis of the retina as a proxy in the assessment of clinical outcomes, such as stroke risk.

Current and novel multi-imaging modalities to assess retinal oxygenation and blood flow

Retinal ischemia characterizes the underlying pathology in a multitude of retinal diseases that can ultimately lead to vision loss. A variety of novel imaging modalities have been developed to characterize retinal ischemia by measuring retinal oxygenation and blood flow in-vivo. These technologies offer valuable insight into the earliest pathophysiologic changes within the retina and provide physicians and researchers with new diagnostic and monitoring capabilities. Future retinal imaging technologies with the capability to provide affordable, noninvasive, and comprehensive data on oxygen saturation, vasculature, and blood flow mechanics are needed. This review will highlight current and future trends in multimodal imaging to assess retinal blood flow and oxygenation.

Heart, Eye, and Artificial Intelligence: A Review

Heart disease continues to be the leading cause of death in the USA. Deep learning-based artificial intelligence (AI) methods have become increasingly common in studying the various factors involved in cardiovascular disease. The usage of retinal scanning techniques to diagnose retinal diseases, such as diabetic retinopathy, age-related macular degeneration, glaucoma and others, using fundus photographs and optical coherence tomography angiography (OCTA) has been extensively documented. Researchers are now looking to combine the power of AI with the non-invasive ease of retinal scanning to examine the workings of the heart and predict changes in the macrovasculature based on microvascular features and function. In this review, we summarize the current state of the field in using retinal imaging to diagnose cardiovascular issues and other diseases.

Use of XyCAM RI for Noninvasive Visualization and Analysis of Retinal Blood Flow Dynamics During Clinical Investigations

INTRODUCTION

Ocular blood flow plays a critical role in eye health by nourishing the retinal and ocular tissues with oxygen and nutrients and removal of ocular metabolic waste. Imaging of retinal and optic blood flow may provide insights for early and more specific diagnoses of ocular vascular disorder and facilitate eye-based biomarkers applicable to neurological health assessment and research.

AREAS COVERED

The ability of the XyCAM RI (Vasoptic Medical Inc., MD, USA) to visualize and to analyze ocular blood flow dynamics XyCAM RI using laser speckle contrast imaging is reviewed and compared with concurrent clinical ophthalmic imaging technologies like optical coherence tomography - angiography (OCT-A), fundus imaging, fluorescein angiography (FA), indocyanine green angiography (ICGA), laser Doppler flowmetry (LDF), and laser speckle flowgraphy (LSFG).

EXPERT OPINION

XyCAM RI, with its unprecedented imaging capabilities to assess blood flow dynamics provides a powerful tool to ophthalmic researchers and doctors to obtain greater clinical insights into the physiological status of the posterior segment and treatment approaches for various diseases in a very patient-friendly, noninvasive manner, unlike dye-based angiographic techniques such as FA or ICG. XyCAM RI is well suited as a modality that could close the gap between current screening and comprehensive eye exams.

Multimodal Retinal Imaging for Detection of Ischemic Stroke

Background: This study aims to evaluate ocular changes in patients with ischemic stroke using multimodal imaging and explore the predictive value of ocular abnormalities for ischemic stroke.

Methods: A total of 203 patients (ischemic stroke group, 62; control group, 141) were enrolled in this study. Basic data from patients, including age; gender; height; weight; history of hypertension, hyperlipidemia, diabetes, alcohol use, and coronary heart disease; and smoking status, were collected. Consequently, Doppler color ultrasound, color fundus photography, and optical coherence tomography (OCT) examinations were conducted. Differences in traditional risk factors and ocular parameters between the two groups were compared, and binary logistic regression was used for multivariate analysis.

Results: The central retinal artery equivalent (CRAE) in the ischemic stroke group was 150.72 ± 20.15 μm and that in the control group was 159.68 ± 20.05 μm. The difference was statistically significant (P = 0.004). Moreover, the subfoveal choroidal thickness (SFChT) in the ischemic stroke group was 199.90 ± 69.27 μm and that in the control group was 227.40 ± 62.20 μm. The difference was statistically significant (P = 0.006). Logistic regression results showed that smoking [odds ratio (OR) = 2.823; 95% confidence interval (95% CI) = 1.477–5.395], CRAE (OR = 0.980; 95% CI = 0.965–0.996), and SFChT (OR = 0.994; 95% CI = 0.989–0.999) are associated with increased risk of ischemic stroke when ocular parameters were combined with traditional risk factors. The area under the receiver operating characteristic (ROC) curve was 0.726, which shows good diagnostic accuracy.

Conclusion: SFChT may be a diagnostic marker for early detection and monitoring of ischemic stroke. Combined with traditional risks, retinal artery diameter, and choroidal thickness, the prediction model can improve ischemic stroke prediction.