A Systematic Review on Retinal Biomarkers to Diagnose Dementia from OCT/OCTA Images

Retinal microvascular density and inner thickness in Alzheimer's disease and mild cognitive impairment

Background

Alzheimer's disease (AD) is a major healthcare challenge, with existing diagnostics being costly/infeasible. This study explores retinal biomarkers from optical coherence tomography (OCT) and OCT angiography (OCTA) as a cost-effective and non-invasive solution to differentiate AD, mild cognitive impairment (MCI), and healthy controls (HCs).

Methods

Participants from the CALLIOPE Research Program were classified as "Dem" (AD and early AD), "MCI," and "HCs" using neuropsychological tests and clinical diagnosis by a neurologist. OCT/OCTA examinations were conducted using the RTVue XR 100 Avanti SD-OCT system (VISIONIX), with retinal parameters extracted. Statistical analysis included normality and homogeneity of variance (HOV) tests to select ANOVA methods. Post-hoc analyses utilized Mann-Whitney U, Dunnett, or Tukey-HSD tests based on parameters' normality and HOV. Correlations with age were assessed via Pearson or Spearman tests. A generalized linear model (GLM) using Tweedie regression modeled the relationship between OCT/OCTA parameters and MMSE scores, correcting for age. Another ordinal logistic GLM (OL-GLM) modeled OCT/OCTA parameters against classes, adjusting for multiple confounders.

Results

We analyzed 357 participants: 44 Dem, 139 MCI, and 174 HCs. Significant microvascular density (VD) reductions around the fovea were linked with MCI and Dem compared to HCs. Age-related analysis associated thickness parameters with HCs' old age. Our OL-GLM demonstrated significant thickness/volume reductions in Inner_Retina and Full_Retina layers. Foveal avascular zone (FAZ) area and perimeter were initially not correlated with cognitive decline; however, OL-GLM significantly associated FAZ perimeter enlargement with Dem and MCI groups. Significant average and inferior peripapillary RNFL thinning were linked to Dem and MCI groups.

Conclusion

This is the first study to examine VD changes in G grid sections among Dem, MCI, and HCs. We found a significant association between various VD parameters and cognitive decline. Most macular thickness/volume changes did not correlate with cognitive decline initially; however, our OL-GLM succeeded, highlighting the importance of the confounders' corrections. Our analysis excluded individual retinal layer parameters due to limitations; however, the literature suggests their value. Our study confirmed existing biomarkers' efficacy and uncovered novel retinal parameters for cognitive decline, requiring further validation.

Retinal assessment in 143 patients with white matter lesions: the potential of OCTA as an evaluation tool

Background

The retina is a simple window to reflect the changes of brain nerves. The aim of this study was to investigate the association between retinal status and white matter lesions (WMLs) in 143 patients aged 50-80 years, utilizing Optical Coherence Tomography Angiography (OCTA) and the Fazekas Visual Scale for assessment.

Methods

A total of 143 subjects underwent MRI scanning to assess the degree of WMLs using the Fazekas scale. Retinal imaging was conducted utilizing OCTA. Multivariate logistic regression analysis was employed to determine the odds ratios and 95% confidence intervals associated with the Fazekas score for each factor. The relationship between cognitive function and various OCTA parameters was assessed using quadratic and cubic simulation curve models. Data following a normal distribution are presented as means, while non-normally distributed data are reported as medians. Qualitative data are expressed as percentages.

Results

As Fazekas grades increased, ILM-IPL thickness (OR = 3.267, OR = 8.436), vessel density in the parafoveal region of the macula, retinal vessel densities (OR = 2.058, OR = 2.363), and RNFL thickness significantly reduced (p < 0.05). With increasing Fazekas scores, the bilateral foveal avascular zone showed a significant increase (OR = 0.362, OR = 0.458) (p < 0.05). Retinal thickness and vascular density were negatively correlated with WMLs, and positively correlated with cognitive function (p < 0.05).

Conclusion

The severity of WMLs increases as retinal thickness and vascular density decrease. OCTA examination has a degree of role in screening for WMLs caused by cerebral microvascular disease. Its effectiveness in screening early asymptomatic individuals or those with mild cognitive impairment is somewhat limited.

Non-Invasive Retinal Biomarkers for Early Diagnosis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the brain associated with ageing and is the most prevalent form of dementia, affecting an estimated 55 million people worldwide, with projections suggesting this number will exceed 150 million by 2050. With its increasing prevalence, AD represents a significant global health challenge with potentially serious social and economic consequences. Diagnosing AD is particularly challenging as it requires timely recognition. Currently, there is no effective therapy for AD; however, certain medications may help slow its progression. Existing diagnostic methods such as magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), and biomarker analysis in cerebrospinal fluid tend to be expensive and invasive, making them impractical for widespread use. Consequently, research into non-invasive biomarkers that enable early detection and screening for AD is a crucial area of contemporary clinical investigation. One promising approach for the early diagnosis of AD may be retinal imaging. As an extension of the central nervous system, the retina offers a distinctive opportunity for non-invasive brain structure and function assessment. Considering their shared embryological origins and the vascular and immunological similarities between the eye and brain, alterations in the retina may indicate pathological changes in the brain, including those specifically related to AD. Studies suggest that structural and vascular changes in the retina, particularly within the neuronal network and blood vessels, may act as markers of cerebral changes caused by AD. These retinal alterations have the potential to act as biomarkers for early diagnosis. Since AD is typically diagnosed only after a significant neuronal loss has occurred, identifying early diagnostic markers could enable timely intervention and help prevent disease progression. Non-invasive retinal imaging techniques, such as optical coherence tomography (OCT) and OCT angiography, provide accessible methods for the early detection of changes linked to AD. This review article focuses on the potential of retinal imaging as a non-invasive biomarker for early diagnosis of AD. Investigating the ageing of the retina and its connections to neurodegenerative processes could significantly enhance the diagnosis, monitoring, and treatment of AD, paving the way for new diagnostic and therapeutic approaches.

Circadian Disruption in Glaucoma: Causes, Consequences, and Countermeasures

This review explores the intricate relationship between glaucoma and circadian rhythm disturbances. As a principal organ for photic signal reception and transduction, the eye plays a pivotal role in coordinating the body's circadian rhythms through specialized retinal ganglion cells (RGCs), particularly intrinsically photosensitive RGCs (ipRGCs). These cells are critical in transmitting light signals to the suprachiasmatic nucleus (SCN), the central circadian clock that synchronizes physiological processes to the 24-hour light-dark cycle. The review delves into the central circadian body clock, highlighting the importance of the retino-hypothalamic tract in conveying light information from the eyes to the SCN. It underscores the role of melanopsin in ipRGCs in absorbing light and initiating biochemical reactions that culminate in the synchronization of the SCN's firing patterns with the external environment. Furthermore, the review discusses local circadian rhythms within the eye, such as those affecting photoreceptor sensitivity, corneal thickness, and intraocular fluid outflow. It emphasizes the potential of optical coherence tomography (OCT) in studying structural losses of RGCs in glaucoma and the associated circadian rhythm disruption. Glaucomatous retinal damage is identified as a cause of circadian disruption, with mechanisms including oxidative stress, neuroinflammation, and direct damage to RGCs. The consequences of such disruption are complex, affecting systemic and local circadian rhythms, sleep patterns, mood, and metabolism. Countermeasures, with implications for glaucoma management, are proposed that focus on strategies to improve circadian health through balanced melatonin timing, daylight exposure, and potential chronotherapeutic approaches. The review calls for further research to elucidate the mechanisms linking glaucoma and circadian disruption and to develop effective interventions to address this critical aspect of the disease.

Blue light reflectance imaging in non-perfusion areas detection: insights from multimodal analysis

DESIGN

A retrospective, cross-sectional image analysis using a convenience sample.

SUBJECTS

Five cases selected based on the availability of comprehensive imaging data.

METHODS

This study involved a retrospective review of images from five cases, focusing on the use of retinal monochromatic blue light reflectance (BLR) imaging to detect non-perfusion areas. Two cases of sickle-cell retinopathy demonstrated peripheral retinal non-perfusion identified through widefield fluorescein angiography. Three other cases-one with branch retinal vein occlusion, one with branch retinal artery occlusion, and one presenting paracentral acute middle maculopathy showed focal macular non-perfusion detected by structural OCT and OCTA. The areas of nonperfused retinal tissue, confirmed by fluorescein angiography, OCT, and OCTA, were then correlated with findings from the BLR image. This correlation aimed to identify any potential associations between these imaging modalities.

MAIN OUTCOME MEASURES

Enhance understanding of the utilization of retinal monochromatic BLR images as a non-perfusion biomarker.

RESULTS

The perfusion defects identified through fluorescein angiography were qualitatively correlated with hypo-reflective regions observed in the BLR images. A notable correlation was also observed between the OCTA deep capillary plexus findings and the BLR images. Additionally, areas of retinal thinning identified on structural OCT thickness maps corresponded with the hypo-reflective regions in the BLR images. This indicates the potential of BLR in identifying non-perfused retinal areas.

CONCLUSIONS

This study reinforces the evidence, through OCT, OCTA, and angiographic correlation, that the BLR can effectively identify areas of retinal non-perfusion in a non-invasive manner. Further research is warranted to assess the method's sensitivity, specificity, and limitations. While the interaction of blue light with the retina, leading to specular reflections and scattering, is established, this research represents a pioneering effort in suggesting which specific retinal structures may be implicated in this phenomenon. This novel insight opens avenues for deeper exploration into the underlying mechanisms and potential clinical applications of utilizing the BLR imaging technique for assessing retinal vascular abnormalities.

Recent advances in neuro-ophthalmology

This review article represents a collaborative effort across continents, bringing together the latest developments in neuro-ophthalmology with a focus on innovative diagnostic and therapeutic modalities that are shaping the future of the field. Among the most significant advancements is the rise of optical coherence tomography (OCT), now recognized as an indispensable tool in neuro-ophthalmological research, providing unparalleled insights into optic nerve and central nervous system pathologies. Gene therapy, particularly for conditions such as Leber's hereditary optic neuropathy, marks a new frontier in personalized medicine, offering hope for previously untreatable conditions. The article also examines the transformative role of telemedicine and artificial intelligence (AI) in clinical practice, which are revolutionizing patient care and enhancing diagnostic precision. Furthermore, it highlights the impact of novel serological biomarkers on the understanding and management of immune-mediated optic neuritis, and discusses the introduction of new therapeutic agents like Tocilizumab and Teprotumumab, which are redefining treatment paradigms. Collectively, these advancements reflect the profound influence of modern medicine on neuro-ophthalmology, paving the way for improved patient outcomes and fostering new avenues for research and clinical practice.

Alzheimer's disease pathophysiology in the Retina

The retina is an emerging CNS target for potential noninvasive diagnosis and tracking of Alzheimer's disease (AD). Studies have identified the pathological hallmarks of AD, including amyloid β-protein (Aβ) deposits and abnormal tau protein isoforms, in the retinas of AD patients and animal models. Moreover, structural and functional vascular abnormalities such as reduced blood flow, vascular Aβ deposition, and blood-retinal barrier damage, along with inflammation and neurodegeneration, have been described in retinas of patients with mild cognitive impairment and AD dementia. Histological, biochemical, and clinical studies have demonstrated that the nature and severity of AD pathologies in the retina and brain correspond. Proteomics analysis revealed a similar pattern of dysregulated proteins and biological pathways in the retina and brain of AD patients, with enhanced inflammatory and neurodegenerative processes, impaired oxidative-phosphorylation, and mitochondrial dysfunction. Notably, investigational imaging technologies can now detect AD-specific amyloid deposits, as well as vasculopathy and neurodegeneration in the retina of living AD patients, suggesting alterations at different disease stages and links to brain pathology. Current and exploratory ophthalmic imaging modalities, such as optical coherence tomography (OCT), OCT-angiography, confocal scanning laser ophthalmoscopy, and hyperspectral imaging, may offer promise in the clinical assessment of AD. However, further research is needed to deepen our understanding of AD's impact on the retina and its progression. To advance this field, future studies require replication in larger and diverse cohorts with confirmed AD biomarkers and standardized retinal imaging techniques. This will validate potential retinal biomarkers for AD, aiding in early screening and monitoring.

Quantitative assessment of retinal vasculature changes in systemic lupus erythematosus using wide-field OCTA and the correlation with disease activity

Purpose

To assess the retinal vasculature changes quantitatively using wide-field optical coherence tomography angiography (OCTA) in systemic lupus erythematosus (SLE), and explore its correlation with systemic clinical features.

Design

Prospective, cross-sectional, observational study.

Participants and controls

Patients with SLE who presented to the Ophthalmology Department of Peking Union Medical College Hospital from November 2022 to April 2023 were collected. The subjects were divided into retinopathy and without retinopathy groups. Age and gender-matched healthy subjects were selected as controls.

Methods

Patients with SLE and control subjects were imaged with 24×20 mm OCTA scans centered on the fovea and 6×6 mm OCTA scans centered on the optic disc. The sub-layers of OCTA images were stratified by the built-in software of the device and then the retinal thickness and vessel density were measured automatically. The characteristics of retinal OCTA parameters of SLE and its correlation with systemic clinical indicators of patients without retinopathy were analyzed.

Main outcome measures

OCTA parameters, visual acuity, intraocular pressure, and systemic clinical indicators of patients such as disease activity index, autoimmune antibodies, and inflammatory marker levels were collected.

Results

A total of 102 SLE patients were included, 24 of which had retinopathy, and 78 had unaffected retina. Wide-field OCTA could effectively detect retinal vascular obstruction, non-perfusion area, and morphological abnormalities in patients with lupus retinopathy. SLE patients without retinopathy had significantly higher retinal superficial vessel density (SVD) in foveal (P=0.02), para-foveal temporal (P=0.01), nasal (P=0.01), peripheral foveal temporal (P=0.02), and inferior areas (P=0.02), as well as subregion temporal (P=0.01) and inferior areas (P=0.03) when compared with healthy controls (n=65 eyes from 65 participants). The area under curve (AUC) value of subregion inferior SVD combined parafoveal temporal SVD was up to 0.70. There was a significantly positive correlation between SVD and disease activity in SLE without retinopathy group. Patients with severe activity had the most significant increase in SVD.

Conclusion

Wide-field OCTA can provide a relatively comprehensive assessment of the retinal vasculature in SLE. In the absence of pathological changes of the retina, the SVD was significantly increased and was positively correlated with the disease activity of SLE.