CHARACTERIZATION BY FRACTAL DIMENSION ANALYSIS OF THE RETINAL CAPILLARY NETWORK IN PARKINSON DISEASE

Neuroretinal and microvascular retinal features in dementia with Lewy body assessed by optical coherence tomography angiography

OBJECTIVE

To explore retinal changes in patients with Dementia with Lewy Bodies (DLB) using Spectral Domain-Optical Coherence Tomography (SD-OCT) and Optical Coherence Tomography Angiography (OCTA), aiming to identify potential biomarkers for diagnosis and monitoring.

METHODS

A cross-sectional study analyzed 15 DLB patients and 18 matched controls. Participants underwent physical, neurological, neuropsychological, and ophthalmological evaluations, including SD-OCT and OCTA. Logistic regression, adjusted for age, sex, and inter-eye correlation, was employed to identify retinal alterations in patients affected by DLB.

RESULTS

OCTA revealed that DLB is associated with reduced superficial and deep vessel densities (SVD and DVD) in the macula (p < 0.01), as well as decreased peripapillary vessel density (ppVD, p < 0.01). SD-OCT parameters showed correlations with DLB, including reduced central macular thickness (CMT, p < 0.001) and thinning of the ganglion cell layer-inner plexiform layer (GCL-IPL, p < 0.01). Logistic regression (R²=0.26) identified reduced ppVD as a significant predictor of DLB (p = 0.030).

CONCLUSIONS

Impairments in retinal capillaries, especially lower ppVD, might mirror cerebral hypoperfusion in DLB, potentially due to reduced Vascular Endothelial Growth Factor (VEGF) levels and increased α-synuclein. Further investigations are warranted to confirm the causal relationship between these observations, disease severity, and progression, as well as their potential role as biomarkers for DLB.

Interocular asymmetry of retinal change in Parkinson's disease

PURPOSE

To investigate interocular asymmetry (IA) of retinal structure and vessel density in patients with Parkinson's disease (PD) and normal controls (NC).

METHODS

Seventy-eight subjects including 40 PD patients and 38 NC had completed optical coherence tomography angiography (OCTA) and neurological examinations for three rating scales (UPDRS-III, MMSE and MoCA). The IA was calculated by the absolute value of difference in right and left eyes. The IA of thickness in macular ganglion cell inner-plexiform layer (GCIPL), peripapillary retinal nerve fiber layer (pRNFL), and vessel density of superficial capillary plexus (SCP), deep capillary plexus (DCP), radial peripapillary capillary (RPC) were obtained from OCTA.

RESULTS

The motor-symptom-onset side of eyes showed lower vessel density in parafovea of SCP (51.09 ± 3.46 vs 49.81 ± 4.16, P = 0.03) and superior hemi of perifovea DCP (49.55 ± 5.81 vs 47.33 ± 5.71, = 0.04). The PD patients showed larger IA in thickness of superior half of pRNFL (5.27 [2.67, 10.87] vs 3.08 [1.62, 5.61], P = 0.02) and parafovea GCIPL (2.40[1.25, 6.35] vs 1.40[0.50, 2.45], P = 0.02). No significant interocular asymmetry was found in vessel density between PD and NC. A higher UPDRS-III scale was associated with larger IA in GCIPL (β = 0.093, P = 0.001) and smaller IA in DCP (β = -0.065, P = 0.037).

CONCLUSION

The motor-symptom-onset side of eyes showed more severe loss of macular vessel density than the other side of eyes. The PD patients showed asymmetrical structural change in GCIPL and pRNFL, which showed the potential as the diagnostic biomarker for PD.

CF-Loss: Clinically-relevant feature optimised loss function for retinal multi-class vessel segmentation and vascular feature measurement

Characterising clinically-relevant vascular features, such as vessel density and fractal dimension, can benefit biomarker discovery and disease diagnosis for both ophthalmic and systemic diseases. In this work, we explicitly encode vascular features into an end-to-end loss function for multi-class vessel segmentation, categorising pixels into artery, vein, uncertain pixels, and background. This clinically-relevant feature optimised loss function (CF-Loss) regulates networks to segment accurate multi-class vessel maps that produce precise vascular features. Our experiments first verify that CF-Loss significantly improves both multi-class vessel segmentation and vascular feature estimation, with two standard segmentation networks, on three publicly available datasets. We reveal that pixel-based segmentation performance is not always positively correlated with accuracy of vascular features, thus highlighting the importance of optimising vascular features directly via CF-Loss. Finally, we show that improved vascular features from CF-Loss, as biomarkers, can yield quantitative improvements in the prediction of ischaemic stroke, a real-world clinical downstream task. The code is available at https://github.com/rmaphoh/feature-loss.

Recent advances in the use of optical coherence tomography in neuro-ophthalmology: A review

Optical coherence tomography (OCT) is an in vivo imaging modality that provides non-invasive, high resolution and fast cross-sectional images of the optic nerve head, retina and choroid. OCT angiography (OCTA) is an emerging tool. It is a non-invasive, dye-free imaging approach of visualising the microvasculature of the retina and choroid by employing motion contrast imaging for blood flow detection and is gradually receiving attention for its potential roles in various neuro-ophthalmic and retinal conditions. We will review the clinical utility of the OCT in the management of various common neuro-ophthalmic and neurological disorders. We also review some of the OCTA research findings in these conditions. Finally, we will discuss the limitations of OCT as well as introduce other emerging technologies.

Deep Learning and Machine Learning Algorithms for Retinal Image Analysis in Neurodegenerative Disease: Systematic Review of Datasets and Models

Purpose

Retinal images contain rich biomarker information for neurodegenerative disease. Recently, deep learning models have been used for automated neurodegenerative disease diagnosis and risk prediction using retinal images with good results.

Methods

In this review, we systematically report studies with datasets of retinal images from patients with neurodegenerative diseases, including Alzheimer's disease, Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, and others. We also review and characterize the models in the current literature which have been used for classification, regression, or segmentation problems using retinal images in patients with neurodegenerative diseases.

Results

Our review found several existing datasets and models with various imaging modalities primarily in patients with Alzheimer's disease, with most datasets on the order of tens to a few hundred images. We found limited data available for the other neurodegenerative diseases. Although cross-sectional imaging data for Alzheimer's disease is becoming more abundant, datasets with longitudinal imaging of any disease are lacking.

Conclusions

The use of bilateral and multimodal imaging together with metadata seems to improve model performance, thus multimodal bilateral image datasets with patient metadata are needed. We identified several deep learning tools that have been useful in this context including feature extraction algorithms specifically for retinal images, retinal image preprocessing techniques, transfer learning, feature fusion, and attention mapping. Importantly, we also consider the limitations common to these models in real-world clinical applications.

Translational Relevance

This systematic review evaluates the deep learning models and retinal features relevant in the evaluation of retinal images of patients with neurodegenerative disease.

Optical Coherence Tomography Angiography: Revolutionizing Clinical Diagnostics and Treatment in Central Nervous System Disease

Optical coherence tomography angiography (OCTA), as a new generation of non-invasive and efficient fundus imaging technology, can provide non-invasive assessment of vascular lesions in the retina and choroid. In terms of anatomy and development, the retina is referred to as an extension of the central nervous system (CNS). CNS diseases are closely related to changes in fundus structure and blood vessels, and direct visualization of fundus structure and blood vessels provides an effective "window" for CNS research. This has important practical significance for identifying the characteristic changes of various CNS diseases on OCTA in the future, and plays a key role in promoting early screening, diagnosis, and monitoring of disease progression in CNS diseases. This article reviews relevant fundus studies by comparing and summarizing the unique advantages and existing limitations of OCTA in various CNS disease patients, in order to demonstrate the clinical significance of OCTA in the diagnosis and treatment of CNS diseases.

Ultra-Widefield Imaging of the Retinal Macrovasculature in Parkinson Disease Versus Controls With Normal Cognition Using Alpha-Shapes Analysis

Purpose

To investigate retinal vascular characteristics using ultra-widefield (UWF) scanning laser ophthalmoscopy in Parkinson disease (PD).

Methods

Individuals with an expert-confirmed clinical diagnosis of PD and controls with normal cognition without PD underwent Optos California UWF imaging. Patients with diabetes, uncontrolled hypertension, glaucoma, dementia, other movement disorders, or known retinal or optic nerve pathology were excluded. Images were analyzed using Vasculature Assessment and Measurement Platform for Images of the Retina (VAMPIRE-UWF) software, which describes retinal vessel width gradient and tortuosity, provides vascular network fractal dimensions, and conducts alpha-shape analysis to further characterize vascular morphology (complexity, Opαmin; spread, OpA).

Results

In the PD cohort, 53 eyes of 38 subjects were assessed; in the control cohort, 51 eyes of 33 subjects were assessed. Eyes with PD had more tortuous retinal arteries in the superotemporal quadrant (P = 0.043). In eyes with PD, alpha-shape analysis revealed decreased OpA, indicating less retinal vasculature spread compared to controls (P = 0.032). Opαmin was decreased in PD (P = 0.044), suggesting increased vascular network complexity. No differences were observed in fractal dimension in any region of interest.

Conclusions

This pilot study suggests that retinal vasculature assessment on UWF images using alpha-shape analysis reveals differences in retinal vascular network spread and complexity in PD and may be a more sensitive metric compared to fractal dimension.

Translational Relevance

Retinal vasculature assessment using these novel methods may be useful in understanding ocular manifestations of PD and the development of retinal biomarkers.

Innovative Macula Capillaries Plexuses Visualization with OCTA B-Scan Graph Representation: Transforming OCTA B-Scan into OCTA Graph Representation

Purpose

The aim of this study is to transform optical coherence tomography angiography (OCTA) scans into innovative OCTA graphs, serving as novel biomarkers representing the macular vasculature.

Patients and Methods

The study included 90 healthy subjects and 39 subjects with various abnormalities (29 with diabetic retinopathy, 5 with age-related macular degeneration, and 5 with choroid neovascularization). OCTA 5µm macular coronal views (MCVs) were generated for each subject, followed by blood vessel segmentation and skeleton processing. Subsequently, the blood vessel density index, blood vessel skeleton index, and blood vessel tortuosity index were computed. The graphs of each metric were plotted against the axial axes of the OCTA B-scan, representing the integrity of vasculature at successive 5µm macular depths.

Results

The results revealed two significant findings. First, the B-scans from OCTA can be transformed into OCTA graphs, yielding three specific OCTA graphs in this study. These graphs provide new biomarkers for assessing the integrity of deep vascular complex (DVC) and superficial vascular complex (SVC) within the macula. Second, a statistically significant difference was observed between normal (n=90) and abnormal (n=39) subjects, with a t-test p-value significantly lower than 0.001. The Mann-Whitney u-test also yielded significant difference but only between the 90 normal and 29 DR subjects.

Conclusion

The novel OCTA graphs offer a unique representation of the macula's SVC and DVC, suggesting their potential in aiding physicians in the diagnosis of eye health within OCTA clinics. Further research is warranted to finalize the shape of these newly derived OCTA graphs and establish their clinical relevance and utility.

Central retina thickness measured with spectral-domain optical coherence tomography in Parkinson disease: A meta-analysis

BACKGROUND

Optical coherence tomography (OCT) can detect visual alterations associated with Parkinson disease, such as damage to the retinal nerve fiber layer or changes in retinal vasculature. Macula thinning in association with Parkinson disease (PD) remains controversial. Therefore, we conducted a meta-analysis to investigate the central retina thickness in PD measured using spectral-domain OCT (SD-OCT).

METHODS

We searched PubMed and the Excerpta Medica database to identify studies that compared macular thickness between patients with PD and healthy controls published before July 31, 2021. A random-effects model was used to examine PD-associated changes in macular thickness. Meta-regression analysis was performed by assessing heterogeneity, publication bias, and study quality.

RESULTS

Thirty-two studies with a cross-sectional design were selected, including 2118 patients with PD and 2338 controls. We identified significant differences in the thickness of the ganglion cell-inner plexiform layer (standardized mean difference [SMD], -0.41; 95% confidence interval [CI], -0.66 to -0.16; I2 = 80%), ganglion cell complex (SMD, -0.33; 95% CI, -0.50 to -0.17; I2 = 0%), and of all inner and outer sectors of the macula (SMD range, -0.21 to -0.56; all P < .05) between patients with PD and controls.

DISCUSSION

These results corroborate the increased prevalence of changes in OCT measures in individuals with PD, highlighting the efficacy of SD-OCT-determined macular thickness as a biomarker for PD. Our findings may provide helpful guidelines for clinicians in rapidly evolving areas of PD diagnosis.

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.

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

BACKGROUND

To examine the association between optical coherence tomography angiography (OCTA) retinal measurements and Parkinson's disease (PD).

METHODS

We searched MEDLINE and EMBASE from inception up to November 5th, 2021 for studies examining the differences between OCTA retinal measurements in PD patients and healthy controls. We used the Hartung-Knapp-Sidik-Jonkman random-effects method to combine study-specific standardized mean differences (SMD) in pooled effect estimates and a meta-analytic extension of the E-value metric to quantify the confounding bias capable of nullifying the pooled estimates.

RESULTS

Nine eligible studies for our systematic review were identified through our search strategy. The pooled SMD between the retinal vessel density of PD patients and healthy participants in the whole superficial vascular plexus (SVP), foveal SVP, parafoveal SVP and foveal avascular zone (FAZ) was -0.68 (95% CI: -1.18 to -0.17, p value = 0.02, n = 7 studies), -0.14 (95% CI: -0.88 to 0.59, p value = 0.62, n = 5 studies), -0.59 (95% CI: -1.41 to 0.23, p value = 0.12, n = 5 studies) and -0.20 (95% CI: -0.79 to 0.38, p value = 0.39, n = 5 studies), respectively. An unmeasured confounder would need to be associated with a 3.01-fold, 1.54-fold, 2.81-fold and 1.70-fold increase in the risk of PD and OCTA retinal measurements, in order for the pooled SMD estimate of vessel density in whole SVP, parafoveal SVP and FAZ, respectively, to be nullified.

CONCLUSIONS

Our results provide evidence on an inverse association between whole SVP vessel density and PD.

Retinal Vessel Density and Retinal Nerve Fiber Layer Thickness: A Prospective Study of One-Year Follow-Up of Patients with Parkinson's Disease

Objective

This study aims to compare the superficial vascular density from the macular region and the retinal nerve fiber layer (RNFL) thickness from the optic disc region between Parkinson's disease (PD) patients and controls.

Methods

We enrolled 56 idiopathic PD patients, totaling 86 eyes (PD group), and 45 sex- and age-matched healthy individuals, amounting to 90 eyes (control group). All subjects underwent examination using Zeiss wide-field vascular optical coherence tomography (OCT) (Cirrus HD-OCT 5000 Carl Zeiss, Germany), with a scanning range of 3 mm × 3 mm. We divided the images into two concentric circles with diameters of 1 mm and 3 mm at the macular fovea's center. Patients with PD were evaluated during their "off" phase using the Unified Parkinson's Disease Rating Scale III (UPDRS-III) and the Hoehn-Yahr scale (H-Y scale) to assess disease severity.

Results

The PD group exhibited significantly lower RNFL thickness (106.13±12.36 μm) compared to the control group (115.95±11.37 μm, P < 0.05). Similarly, the superficial retinal vessel length density was significantly lower in the PD group (20.7 [19.62, 22.17] mm-1) than in the control group (21.79±1.16 mm-1, P < 0.05). Correlation analysis revealed a negative correlation between RNFL thickness and UPDRS III score (rs=-0.036, P=0.037), and RNFL thickness tended to decrease with increasing severity of movement disorders. However, during the 6 and 12-month follow-up of some PD patients, we observed no progressive thinning of the RNFL or decreased superficial vascular density.

Conclusion

PD patients show retinal structural damage characterized by RNFL thinning and reduced retinal vessel length density. However, RNFL thickness did not correlate with vascular density nor did it decrease with the disease's progression.

Clinical Observation of Macular Superficial Capillary Plexus and Ganglion Cell Complex in Patients with Parkinson's Disease

INTRODUCTION

We investigated macular superficial capillary plexus (SCP) density and the thicknesses of the ganglion cell complex (GCC) in patients with Parkinson's disease (PD) and correlated them. We also observed the correlations between SCP density and clinical parameters of PD patients. The retina might be a novel biomarker of PD and will be useful in the future for the early diagnosis of PD and detecting disease progression.

METHODS

Seventy-four participants (38 patients with PD and 36 healthy controls) were recruited at the Affiliated Hospital of Xuzhou Medical University between January 2022 and June 2022 in this study. The macular SCP densities was measured by optical coherence tomography angiography (OCTA), and the GCC thickness was measured by optical coherence tomography (OCT). The parameters were compared between PD patients and healthy controls. The correlation between SCP and clinical parameters was tested.

RESULTS

Compared with the control group, PD patients showed reduced SCP densities in all areas of the macular region (parafovea-temporal: t = 3.053, p = 0.003; parafovea-superior: t = 3.680, p = 0.001; parafovea-nasal: t = 4.643, p < 0.001; parafovea-inferior: t = 2.254, p = 0.027; perifovea-temporal: t = 3.798, p < 0.001; perifovea-superior: t = 3.014, p = 0.004; perifovea-nasal: t = 2.948, p = 0.004; perifovea-inferior: t = 3.337, p = 0.021). The average GCC thickness in the PD patients was significantly reduced (t = 2.365, p = 0.021). There were positive correlations between the average GCC thickness and the SCP densities in most of the areas of the macular regions in PD patients (parafovea-temporal: r = 0.325, p = 0.005; parafovea-superior: r = 0.295, p = 0.011; parafovea-nasal: r = 0.335, p = 0.003; perifovea-superior: r = 0.362, p = 0.002; perifovea-nasal: r = 0.290, p = 0.012; perifovea-inferior: r = 0.333, p = 0.004). We found significant correlations between SCP densities and Hoehn and Yahr (H and Y) scales, UPDRS III scores, and MMSE scores. No significant correlation was observed between SCP density and PD disease duration (all p > 0.05).

CONCLUSIONS

We demonstrated that the macular SCP density was decreased, and the average GCC thickness was reduced in PD patients. The correlation between SCP density damage and GCC thinning also suggested that the retinal microvascular damage may be associated with retinal structural degeneration in PD patients. OCTA and OCT may be considered objective biomarkers for detecting microvascular impairment and neuronal damage in the early stages of PD in the future.

Multimodal Retinal Imaging in Patients with Diabetes Mellitus and Association with Cerebrovascular Disease

INTRODUCTION

This study aimed to evaluate the association between macular optical coherence tomography angiography (OCT-A) metrics, characteristics of ultrawide field (UWF) imaging, and cerebrovascular disease in patients with diabetes mellitus (DM) with different stages of diabetic retinopathy (DR).

METHODS

516 eyes of 258 DM patients were enrolled in two centers (Milan and Belfast). UWF color fundus photos (CFPs) were obtained with Optos California (Optos, PLC) and graded for both DR severity and predominantly peripheral lesions presence (>50% of CFP lesions) by two independent graders. OCT-A (3 × 3 mm), available in 252 eyes of 136 patients, was used to determine perimeter, area, and circularity index of the foveal avascular zone and vessel density (VD); perfusion density (PD); fractal dimension on superficial, intermediate (ICP), and deep capillary plexuses; flow voids (FVs) in the choriocapillaris.

RESULTS

Out of 516 eyes, 108 eyes (20.9%) had no DR, and 6 eyes were not gradable. The remaining 402 eyes were as follows: 10.3% (53) had mild nonproliferative DR (NPDR), 38.2% (197) had moderate NPDR, 11.8% (61) had severe NPDR, and 17.6% (91) had proliferative DR. A worse DR stage was associated with a history of stroke (p = 0.044). Logistic regression analysis after taking into account sex, type of DM, age, DM duration, and OCT-A variables found that PD and VD on ICP were significantly associated with presence of stroke and DR severity.

CONCLUSION

OCT-A metrics show an association with the presence of cerebrovascular complications, providing potentially useful parameters to estimate vascular risk in patients with DM.

Central retinal microvasculature damage is associated with orthostatic hypotension in Parkinson's disease

Orthostatic hypotension (OH) is a common non-motor symptom in Parkinson's disease (PD). OH can cause cerebral and retinal hypoperfusion and is associated with microvascular damage in PD. Optical coherence tomography angiography (OCTA) is a non-invasive technology that can be used to visualize the retinal microvasculature and detect microvascular damage in PD. In the present study, 51 PD patients (OH+, n = 20, 37 eyes; OH-, n = 32, 61 eyes) and 51 healthy controls (100 eyes) were evaluated. The Unified Parkinson's Disease Rating Scale III, Hoehn and Yahr scale, Montreal Cognitive Assessment, levodopa equivalent daily dose, and vascular risk factors, including hypertension, diabetes, and dyslipidemia, were investigated. PD patients underwent a head-up tilt (HUT) test. The PD patients had a lower superficial retinal capillary plexus (SRCP) density in the central region than control patients. The PDOH+ group had lower vessel density in the SRCP of the central region compared with the control group and lower vessel density in the DRCP of the central region than the PDOH- and control groups. The changes in systolic and diastolic blood pressure during the HUT test in PD patients showed a negative correlation with the vessel density in the DRCP central region. The presence of OH was a critical factor associated with central microvasculature damage in PD. These findings indicate that OCTA can be a useful and non-invasive tool for detecting microvasculature damage in PD patients.

Inner retinal layers' alterations of the microvasculature in early stages of Parkinson's disease: a cross sectional study

PURPOSE

To investigate microcirculation characteristics of the inner retinal layers at the macula and the peripapillary area using Optical Coherence Tomography Angiography (OCT-A) of patients in early stages of Parkinson's disease (PD).

METHODS

32 PD patients and 46 age- and gender-matched healthy controls were included in this cross sectional study. OCT-A imaging was performed to analyze microcirculation characteristics at each separate macular region (fovea, parafovea, and perifovea) and the peripapillary area of the inner retinal layers.

RESULTS

Individuals with PD had significantly lower parafoveal, perifoveal and total vessel density (VD) in the superficial capillary plexus (SCP) than controls (all p < 0.001), while foveal VD was higher in PD eyes than that of controls, though not statistically significant. Similarly, individuals with PD had significantly lower parafoveal, perifoveal and total perfusion in the SCP than control eyes (all p < 0.001), while foveal perfusion was significantly higher in PD eyes than that of controls (p = 0.008). PD eyes had significantly smaller FAZ area and perimeter accompanied by decreased circularity at the SCP as compared to controls (all p < 0.001). Concerning the peripapillary area, individuals with PD had significantly lower radial peripapillary capillary perfusion density and flux index at the SCP than controls (all p < 0.001). All p values remained statistically significant even after using the Bonferroni correction for multiple comparisons, except for that of foveal perfusion.

CONCLUSIONS

Our study indicates alterations of the inner retinal layers at the macula and the peripapillary area at the preliminary stages of PD. OCT-A parameters could potentially comprise imaging biomarkers for PD screening and improve the diagnostic algorithms.

Evaluation of retina and microvascular changes in the patient with Parkinson's disease: A systematic review and meta-analysis

Background

Parkinson's disease (PD) is a multifaceted neurodegenerative disease. The optic nerve, as a window into the central nervous system (CNS), is known to be an important part of the CNS and can be detected non-invasively. With the widespread availability of optical coherence tomography (OCT) devices, an increasing number of studies have paid attention to the neuropathological disorders in the retina of PD patients in recent years. However, it is still controversial whether OCT can be used as a complementary tool for PD diagnosis.

Methods

This review is registered with PROSPERO, number CRD42022301258. The Embase, PUBMED, and The Cochrane Library databases were independently retrieved by 2 investigators to identify relevant papers published from 1 January 2017 to 24 January 2022. These studies used OCT or OCTA to evaluate the difference in the retinal nerve fiber layer (RNFL) thickness, ganglion cell layer(GCL) thickness, macula thickness, Cup and disk area superficial retinal capillary plexus (SCP), and deep retinal capillary plexus(DCP). The standard mean difference (SMD) with the 95% confidence interval (CI) was pooled for continuous outcomes.

Results

In total, 26 studies had been enrolled in this meta-analysis with a total number of 2,790 eyes, including 1,343 eyes from the PD group along with 1,447 eyes from the HC group. The results revealed that the RNFL thickness (SMD: -0.53; 95%CI, -0.71∼-0.35; P < 0.00001), GCL thickness (SMD: -0.43; 95%CI, -0.66 to -0.19; P = 0.0003), macula thickness (SMD: -0.22; 95%CI, -0.22 to -0.11; P < 0.0001) were significantly thinner in patients with PD. The SCP (SMD: -0.61; 95%CI, -1.31to -0.10; P = 0.02) was significantly lower in PD patients. The DCP (SMD: -0.48; 95%CI, -1.02 to -0.06; P = 0.08) is lower in PD patients, but the difference was statistically insignificant.

Conclusion

Retinal nerve fiber layer thickness, GCL thickness, macular thickness, and SVD of PD patients are lower than those of healthy control. OCT and OCTA could detect morphological retinal changes in PD and might be objective and reproducible auxiliary tools to assist clinician diagnosis.

Systematic review registration

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42022301258].

Repeatability and Reproducibility of Retinal Fractal Dimension Measured with Swept-Source Optical Coherence Tomography Angiography in Healthy Eyes: A Proof-of-Concept Study

The retinal vascular network fractal dimension (FD) could be a promising imaging biomarker. Our objective was to evaluate its repeatability and reproducibility in healthy eyes. A cross-sectional study was undertaken with young, healthy volunteers who had no reported cardiac risk factors or ocular disease history. For each participant, three SS-OCTA images (12 × 12 mm) were acquired using the Plex Elite 9000 (Carl Zeiss Meditec AG, Jena, Germany) by two ophthalmologists. Automated segmentation was obtained from both the superficial and deep capillary plexuses. FD was estimated by box counting. The intraclass correlation coefficients (ICC) were used as measures for repeatability and reproducibility. A total of 43 eyes of healthy volunteers were included. The mean ± standard deviation (SD) age was 30 ± 6.2 years. The results show good repeatability. The ICC was 0.722 (95% CI, 0.541–0.839) in the superficial capillary plexus and 0.828 (95% CI, 0.705–0.903) in the deep capillary plexus. For reproducibility, the ICC was 0.651 (95% CI, 0.439–0.795) and 0.363 (95% CI, 0.073–0.596) at the superficial and deep capillary plexus, respectively. In this study, the FD of the vascular network measured via SS-OCTA showed good repeatability and reproducibility in healthy participants.

Ocular Factors of Fractal Dimension and Blood Vessel Tortuosity Derived From OCTA in a Healthy Chinese Population

Purpose

To identify the ocular factors of microvascular fractal dimension (FD) and blood vessel tortuosity (BVT) of macula measured with optical coherence tomography angiography (OCTA) in a healthy Chinese population.

Methods

Healthy subjects without ocular disorders were recruited at Zhongshan Ophthalmic Center. The FD and BVT in the superficial capillary plexus (SCP) and deep capillary plexus (DCP) at the macula were obtained from OCTA images. The FD was calculated using the box-counting method, and the BVT was defined as the ratio of the actual distance between two points to the straight distance on the skeletonized image. Univariate and stepwise multivariate linear regression analyses were performed to identify the ocular factors of FD and BVT, and the results are presented as coefficients and 95% confidence intervals (CIs). Only the right eye of each subject was included.

Results

A total of 2189 healthy individuals (2189 eyes) were included with a mean age of 49.9 ± 13.2 years; 54.4% were female. In the multivariate model, the FD in the SCP was significantly associated with higher intraocular pressure (IOP) (β = 0.204; 95% CI, 0.073-0.335; P < 0.001), axial length (AL) (β = -0.875; 95% CI, -1.197 to -0.552; P < 0.001; R2 = 0.26; root mean square error [RMSE] = 7.78). The FD in the DCP was significantly associated with best-corrected visual acuity (β = -6.170; 95% CI, -10.175 to -2.166; P = 0.003) and anterior chamber depth (β = -0.348; 95% CI, -0.673 to -0.023; P = 0.036; R2 = 0.10; RMSE = 2.58). Superficial BVT was independently associated with IOP (β = -0.044; 95% CI, -0.079 to -0.009; P = 0.012) and AL (β = 0.097; 95% CI, 0.014-0.181; P = 0.022; R2 = 0.15; RMSE = 2.02). Deep BVT was independently associated with IOP (β = -0.004; 95% CI, -0.009 to -0.0005; P = 0.028) and lens thickness (β = 0.036, 95% CI, 0.003-0.060; P = 0.028; R2 = 0.07, RMSE = 0.25).

Conclusions

The IOP and AL were dependent ocular parameters variables of FD and BVT in the SCP in this healthy population. The FD in the DCP was also influenced by visual acuity and anterior chamber depth. These factors should be considered when microvascular geometrics are used in the future studies.

Translational Relevance

This work discovered the influence factors of OCTA geometrics parameters for further establishment of diagnostic model or method for glaucoma and other microvasculature-related ocular diseases.

Elevated α-synuclein and NfL levels in tear fluids and decreased retinal microvascular densities in patients with Parkinson's disease

The pathognomonic hallmark of Parkinson's disease (PD), α-synuclein, has been observed in the retina of PD patients. We investigated whether biomarkers in the tears and retinal microvascular changes associate with PD risk and progression. This prospective study enrolled 49 PD patients and 45 age-matched healthy controls. The α-synuclein and neurofilament light chain (NfL) levels were measured using an electrochemiluminescence immunoassay. Retinal vessel density was assessed using optical coherence tomography angiography (OCT-A). The Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and Mini-Mental State Examination score were used to assess motor and cognitive progression. The α-synuclein and NfL levels in the tears were higher in PD patients than in controls (α-synuclein: 55.49 ± 8.12 pg/mL vs. 31.71 ± 3.25 pg/mL, P = 0.009; NfL: 2.89 ± 0.52 pg/mL vs. 1.47 ± 0.23 pg/mL, P = 0.02). The vessel densities in the deep plexus of central macula and the radial peripapillary capillary layer of disc region were lower in PD patients with moderate-stage compared with early-stage PD (P < 0.05). The accuracy of predicting PD occurrence using age and sex alone (area under the curve [AUC] 0.612) was significantly improved by adding α-synuclein and NfL levels and retinal vascular densities (AUC 0.752, P = 0.001). After a mean follow-up of 1.5 ± 0.3 years, the accuracy of predicting motor or cognitive progression using age, sex, and baseline motor severity as a basic model was increased by incorporating retinal microvascular and biofluid markers as a full model (P = 0.001). Our results showed that retinal microvascular densities combined with α-synuclein and NfL levels in tears are associated with risk and progression of PD.

Retinal age gap as a predictive biomarker of future risk of Parkinson's disease

Introduction

retinal age derived from fundus images using deep learning has been verified as a novel biomarker of ageing. We aim to investigate the association between retinal age gap (retinal age–chronological age) and incident Parkinson’s disease (PD).

Methods

a deep learning (DL) model trained on 19,200 fundus images of 11,052 chronic disease-free participants was used to predict retinal age. Retinal age gap was generated by the trained DL model for the remaining 35,834 participants free of PD at the baseline assessment. Cox proportional hazards regression models were utilised to investigate the association between retinal age gap and incident PD. Multivariable logistic model was applied for prediction of 5-year PD risk and area under the receiver operator characteristic curves (AUC) was used to estimate the predictive value.

Results

a total of 35,834 participants (56.7 ± 8.04 years, 55.7% female) free of PD at baseline were included in the present analysis. After adjustment of confounding factors, 1-year increase in retinal age gap was associated with a 10% increase in risk of PD (hazard ratio [HR] = 1.10, 95% confidence interval [CI]: 1.01–1.20, P = 0.023). Compared with the lowest quartile of the retinal age gap, the risk of PD was significantly increased in the third and fourth quartiles (HR = 2.66, 95% CI: 1.13–6.22, P = 0.024; HR = 4.86, 95% CI: 1.59–14.8, P = 0.005, respectively). The predictive value of retinal age and established risk factors for 5-year PD risk were comparable (AUC = 0.708 and 0.717, P = 0.821).

Conclusion

retinal age gap demonstrated a potential for identifying individuals at a high risk of developing future PD.

Retinal Microvascular Density Was Associated With the Clinical Progression of Parkinson’s Disease

Background

Retinal microvascular density has been studied in neurodegenerative diseases, whereas patients with Parkinson’s disease (PD) at different clinical stages have been rarely investigated. The present study aimed to evaluate the microvascular variations in superficial retinal capillary plexus (SCP) in patients with PD on different Hoehn-Yahr (H-Y) stages by optical coherence tomography angiography (OCTA), as well as determine their relationships with clinical parameters.

Methods

In total, 115 patients with PD and 67 healthy controls (HCs) were recruited. The PD group was divided into three groups based on the H-Y stage. The OCTA examination was performed in all participants, and the macular vessel density (m-VD), peripapillary vessel density (p-VD), and foveal avascular zone (FAZ) area were measured.

Results

The m-VD in all regions, p-VD in center [6.1 (4.8, 6.95) mm^–1 in healthy eyes vs. 5.1 (3.7, 6.4) mm^–1 in patients], nasal inner (NI) [18.5 (17.8, 19.3) mm^–1 in healthy eyes vs. 17.9 (17.1, 18.7) mm^–1 in patients], temporal outer (TO) [19.6 (18.9, 20.2) mm^–1 in healthy eyes vs. 19.3 (18.5, 19.7) mm^–1 in patients] regions and FAZ area [0.36 (0.32, 0.39) mm² in healthy eyes vs. 0.29 (0.26, 0.33) mm² in patients] noticeably decreased in PD groups compared with HC (p < 0.05). Moreover, the FAZ area was suggested to decline significantly in patients with PD with H-Y I stage (p < 0.05), while it was more serious in the H-Y III stage in patients. Furthermore, we found that m-VD exhibited a significant negative correlation with age, disease duration, UPDRS scores, NMSS scores, and H-Y stage.

Conclusion

OCTA has the potential to non-invasively detect the microvascular changes in patients with PD with different clinical stages in vivo, and it may be a valuable tool to monitor the PD progression.

Retinal Degeneration: A Window to Understand the Origin and Progression of Parkinson’s Disease?

Parkinson’s disease (PD), the second most prevalent neurodegenerative disorder, manifests with motor and non-motor symptoms associated with two main pathological hallmarks, including the deterioration of dopaminergic cells and aggregation of alpha-synuclein. Yet, PD is a neurodegenerative process whose origin is uncertain and progression difficult to monitor and predict. Currently, a possibility is that PD may be secondary to long lasting peripheral affectations. In this regard, it has been shown that retinal degeneration is present in PD patients. Although it is unknown if retinal degeneration precedes PD motor symptoms, the possibility exists since degeneration of peripheral organs (e.g., olfaction, gut) have already been proven to antedate PD motor symptoms. In this paper, we explore this possibility by introducing the anatomical and functional relationship of retina and brain and providing an overview of the physiopathological changes of retinal structure and visual function in PD. On the basis of the current status of visual deficits in individuals with PD, we discuss the modalities and pathological mechanism of visual function or morphological changes in the retina and focus on the correlation between visual impairment and some representative structural features with clinical significance. To consider retinal degeneration as a contributor to PD origin and progress is important because PD evolution may be monitored and predicted by retinal studies through state-of-the-art techniques of the retina. It is significant to integrally understand the role of retinal morphological and functional changes in the neurodegenerative process for the diagnosis and therapeutic strategies of PD.

Association of Serum Uric Acid With Retinal Capillary Plexus

BACKGROUND

To determine the association between serum uric acid (SUA) and the retinal capillary plexus (RCP) using optical coherence tomography angiography (OCTA).

METHODS

This cross-sectional study evaluated data from August 2019 to January 2020 from participants recruited from the Jidong community (Tangshan, Hebei, China). All participants completed detailed anthropometrical measurements, laboratory tests and comprehensive ophthalmic examinations. We assessed the vessel density in RCP using OCTA. We used multivariable analysis to evaluate the sex-specific association between SUA and RCP after adjusting for confounders.

RESULTS

A total of 2730 participants were included in this study. The mean age of the participants was 44.0 ± 11.6 years, and 1463 (53.6%) were women. The multivariable βs and 95% confidence intervals (CIs) of superficial RCP vessel density in the second through fourth SUA quartiles compared with the lowest SUA quartiles were -0.27 (-0.56 - 0.03), -0.30 (-0.60 - 0.01), and -0.46 (-0.78 - -0.14) (P for trend = 0.007) in men.

CONCLUSIONS

Higher SUA levels were significantly associated with lower RCP vessel density in men. Our findings provide evidence for the detrimental effect of high SUA levels on the retinal microvasculature and imply the importance of modulating SUA to prevent the microvascular alternation especially for men.

Dopaminergic Basis of Spatial Deficits in Early Parkinson's Disease

Dopaminergic mechanisms regulating cognitive and motor control were evaluated comparing visuoperceptual and perceptuomotor functions in Parkinson's disease (PD). The performance of PD patients (n = 40) was contrasted with healthy controls (n = 42) across two separate visits (on and off dopaminergic medications) on computerized tasks of perception and aiming to a target at variable stimulus lengths (4, 8, 12 cm). Novel visuoperceptual tasks of length equivalence and width interval estimations without motor demands were compared with tasks estimating spatial deviation in movement termination. The findings support the presence of spatial deficits in early PD, more pronounced with increased discrimination difficulty, and with shorter stimulus lengths of 4 cm for both visuoperceptual and perceptumotor functions. Dopaminergic medication had an adverse impact on visuoperceptual accuracy in particular for length equivalence estimations, in contrast with dopaminergic modulation of perceptuomotor functions that reduced angular displacements toward the target. The differential outcomes for spatial accuracy in perception versus movement termination in PD are consistent with involvement of the direct pathway and models of progressive loss of dopamine through corticostriatal loops. Future research should develop validated and sensitive standardized tests of perception and explore dopaminergic selective deficits in PD to optimize medication titration for motor and cognitive symptoms of the disease.

Macular microcirculation characteristics in Parkinson's disease evaluated by OCT-Angiography: a literature review

PURPOSE

Given the fact that retina may provide a window into the central nervous system, there has been interest in identifying retinal biomarkers as predicting factors of pathological processes in neurodegenerative disorders. Emerging evidence has suggested that macular microcirculation changes in Parkinson disease (PD) may indicate the alterations of cerebral microvasculature. The use of Optical Coherence Tomography Angiography (OCT-A) has attracted significant attention in recent years as this technique offers a detailed analysis of the existence of changes at the macular capillary plexus.

METHODS

A detailed review of the literature was performed in PubMed until June 2021. We identified all papers referring to the alterations of the macular capillary plexus in PD using OCT-A.

RESULTS

A comprehensive update indicates that microvasculature alterations of the macular capillary plexus utilizing OCT-A may comprise useful biomarkers regarding the cerebral vasculature in PD. Since the available evidence is limited, additional studies are warranted to establish the OCT-A parameters as predicting factors in clinical practice.

CONCLUSIONS

A review of the existing literature sheds light on the microvasculature changes of the macular capillary plexus as seen on OCT-A in PD patients. The current article discusses notable aspects of key publications on the topic, highlights the importance of the potential long-term effectiveness of OCT-A biomarkers in PD and proposes the need for further future research.

Visual Impairments Are Associated With Retinal Microvascular Density in Patients With Parkinson's Disease

Objective

This study aimed to evaluate retinal microvascular density in patients with Parkinson’s disease (PD) and its correlation with visual impairment.

Methods

This cross-sectional study included 24 eyes of 24 patients with PD and 23 eyes of 23 healthy controls. All participants underwent ophthalmic examination, visual evoked potential (VEP) test, 25-item National Eye Institute Visual Function Questionnaire (NEI VFQ-25), and optical coherence tomography angiography (OCTA) examination. The correlation between retinal microvascular density and visual parameter was evaluated using Spearman correlation analysis, and the area under receiver operating characteristic curve (AUROC) was calculated.

Results

Parkinson’s disease patients had prolonged P100 latency (P = 0.041), worse vision-related quality of life (composite score and 3 of 12 subscales in NEI VFQ-25), and decreased vessel density (VD) in all sectors of 3-mm-diameter region (all P < 0.05) compared with healthy controls. There were no statistical differences in the ganglion cell-inner plexiform layer (GCIPL) thickness and retinal nerve fiber layer (RNFL) thickness between the two groups. A negative correlation was found between P100 latency and nasal and superior sectors of macular VD in a 3-mm-diameter region (r = −0.328, P = 0.030; r = −0.302, and P = 0.047, respectively). Macular VD in a 3-mm-diameter region showed diagnostic capacities to distinguish PD patients from healthy controls (AUROCs, ranging from 0.655 to 0.723).

Conclusion

This study demonstrated that decreased retinal microvascular density was correlated with visual impairment in PD patients. Retinal microvasculature change may occur earlier than visual decline and retinal structure change and has the potential to be a promising diagnostic marker for early PD.

Retinal Flow Density Changes in Early-stage Parkinson's Disease Investigated by Swept-Source Optical Coherence Tomography Angiography

Background: Parkinson's Disease (PD) is the second-most common neurodegenerative disease affecting the elderly population. The eye has been referred to as a window to the brain due to its inseparable relationship with the central nervous system. The development of Swept-Source Optical Coherence Tomography (SS-OCT) and Optical Coherence Tomography Angiography (OCTA) technologies has offered us a better imaging modality to study the impact of PD on the retina.Method: Seventy-five eyes of 42 early-stage PD patients and 150 eyes of 75 matched healthy controls were enrolled in the current study. We performed SS-OCT and SS-OCTA to assess retinal nerve fiber layer (RNFL), ganglion cell layer (GCL) + inner plexiform layer (IPL), internal nuclear layer (INL) thickness, and retinal flow density and flow ratio.Results: Our study indicates decreasing superficial and deep flow density in most regions of the retina. Superficial and deep flow parameters were also associated with RNFL, GCL+IPL, and INL thickness. ROC analysis reveals superficial flow density demonstrated an Area Under Curve (AUC) of 0.688, which is greater than deep flow density and retinal thickness measurements.Conclusion: To the best of our knowledge, we are the first study using SS-OCT and SS-OCTA to study superficial and deep retinal flow changes in early-stage PD patients. Our study suggests decreasing retinal flow density provides greater diagnostic power than retinal thickness measurements in the early stage of PD. SS-OCTA parameters could potentially serve as imaging biomarkers in PD diagnosis and staging.

Foveal Remodeling of Retinal Microvasculature in Parkinson's Disease

Background

Retinal microvascular alterations have been previously described in Parkinson’s disease (PD) patients using optical coherence tomography angiography (OCT-A). However, an extensive description of retinal vascular morphological features, their association with PD-related clinical variables and their potential use as diagnostic biomarkers has not been explored.

Methods

We performed a cross-sectional study including 49 PD patients (87 eyes) and 40 controls (73 eyes). Retinal microvasculature was evaluated with Spectralis OCT-A and cognitive status with Montreal Cognitive Assessment. Unified PD Rating Scale and disease duration were recorded in patients. We extracted microvascular parameters from superficial and deep vascular plexuses of the macula, including the area and circularity of foveal avascular zone (FAZ), skeleton density, perfusion density, vessel perimeter index, vessel mean diameter, fractal dimension (FD) and lacunarity using Python and MATLAB. We compared the microvascular parameters between groups and explored their association with thickness of macular layers and clinical outcomes. Data were analyzed with General Estimating Equations (GEE) and adjusted for age, sex, and hypertension. Logistic regression GEE models were fitted to predict diagnosis of PD versus controls from microvascular, demographic, and clinical data. The discrimination ability of models was tested with receiver operating characteristic curves.

Results

FAZ area was significantly smaller in patients compared to controls in superficial and deep plexuses, whereas perfusion density, skeleton density, FD and lacunarity of capillaries were increased in the foveal zone of PD. In the parafovea, microvascular parameters of superficial plexus were associated with ganglion cell-inner plexiform layer thickness, but this was mainly driven by PD with mild cognitive impairment. No such associations were observed in controls. FAZ area was negatively associated with cognition in PD (non-adjusted models). Foveal lacunarity, combined with demographic and clinical confounding factors, yielded an outstanding diagnostic accuracy for discriminating PD patients from controls.

Conclusion

Parkinson’s disease patients displayed foveal microvascular alterations causing an enlargement of the vascular bed surrounding FAZ. Parafoveal microvascular alterations were less pronounced but were related to inner retinal layer thinning. Retinal microvascular abnormalities helped discriminating PD from controls. All this supports OCT-A as a potential non-invasive biomarker to reveal vascular pathophysiology and improve diagnostic accuracy in PD.

Ocular biomarkers and their role in the early diagnosis of neurocognitive disorders

Given the fact that different types of dementia can be diagnosed only postmortem or when the disease has progressed enough to cause irreversible damage to certain brain areas, there has been an increasing need for the development of sensitive and reliable methods that can detect early preclinical forms of dementia, before the symptoms have even appeared. Ideally, such a method would have the following characteristics: to be inexpensive, sensitive and specific, Non-invasive, fast and easily accessible. The ophthalmologic examination and especially the study of the retina, has caught the attention of many researchers, as it can provide a lot of information about the CNS and it fulfills many of the aforementioned criteria. Since the introduction of the non-invasive optical coherence tomography (OCT) and the newly developed modality OCT-angiography (OCT-A) that can demonstrate the structure and the microvasculature of the retina and choroid, respectively, there have been promising results regarding the value of the ophthalmologic examination in the early diagnosis of Alzheimer's disease. In this review paper, we summarize and discuss the ocular findings in patients with cognitive impairment disorders and we highlight the importance of the ophthalmologic examination to the diagnosis of these disorders.

Characterization of Retinal Microvascular and Choroidal Structural Changes in Parkinson Disease

Importance

Noninvasive retinal imaging may detect structural changes associated with Parkinson disease (PD) and may represent a novel biomarker for disease detection.

Objective

To characterize alterations in the structure and microvasculature of the retina and choroid in eyes of individuals with PD and compare them with eyes of age- and sex-matched cognitively healthy control individuals using optical coherence tomography (OCT) and OCT angiography (OCTA).

Design, Setting, and Participants

This cross-sectional study was conducted at the Duke Neurological Disorders Clinic in Durham, North Carolina. Individuals aged 50 years or older with a diagnosis of PD were eligible for inclusion and underwent an evaluation and diagnosis confirmation before enrollment. Control individuals aged 50 years or older and without subjective cognitive dysfunction, a history of tremor, or evidence of motor dysfunction consistent with parkinsonism were solicited from the clinic or the Duke Alzheimer's Disease Prevention Registry. Individuals with diabetes, glaucoma, retinal pathology, other dementias, and corrected Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity worse than 20/40 Snellen were excluded. Data were analyzed between January 1, 2020, and March 30, 2020.

Exposures

All participants underwent OCT and OCTA imaging.

Main Outcomes and Measures

Generalized estimating equation analysis was used to characterize the association between imaging parameters and PD diagnosis. Superficial capillary plexus vessel density (VD) and perfusion density (PFD) were assessed within the ETDRS 6 × 6-mm circle, 6 × 6-mm inner ring, and 6 × 6-mm outer ring, as was the foveal avascular zone area. Peripapillary retinal nerve fiber layer thickness, macular ganglion cell-inner plexiform layer thickness, central subfield thickness, subfoveal choroidal thickness, total choroidal area, luminal area, and choroidal vascularity index (CVI) were measured.

Results

A total of 124 eyes of 69 participants with PD (39 men [56.5%]; mean [SD] age, 71.7 [7.0] years) and 248 eyes of 137 control participants (77 men [56.2%]; mean [SD] age, 70.9 [6.7] years) were analyzed. In the 6 × 6-mm ETDRS circle, VD (β coefficient = 0.37; 95% CI, 0.04-0.71; P = .03) and PFD (β coefficient = 0.009; 95% CI, 0.0003-0.018; P = .04) were lower in eyes of participants with PD. In the inner ring of the 6 × 6-mm ETDRS circle, VD (β coefficient = 0.61; 95% CI, 0.20-1.02; P = .003) and PFD (β coefficient = 0.015; 95% CI, 0.005-0.026; P = .004) were lower in eyes of participants with PD. Total choroidal area (β coefficient = -1.74 units2; 95% CI, -3.12 to -0.37 units2; P = .01) and luminal area (β coefficient = -1.02 units2; 95% CI, -1.86 to -0.18 units2; P = .02) were greater, but CVI was lower (β coefficient = 0.5%; 95% CI, 0.2%-0.8%; P < .001) in eyes of individuals with PD.

Conclusions and Relevance

This study found that individuals with PD had decreased retinal VD and PFD as well as choroidal structural changes compared with age- and sex-matched control participants. Given the observed population differences in these noninvasive retinal biomarkers, further research into their clinical utility in PD is needed.

Identifying Peripapillary Radial Capillary Plexus Alterations in Parkinson's Disease Using OCT Angiography

PURPOSE

To compare radial peripapillary capillary (RPC) plexus vascular parameters and retinal nerve fiber layer (RNFL) thickness between those with Parkinson's disease (PD) and controls.

DESIGN

Prospective, cross-sectional study.

PARTICIPANTS

A total of 151 eyes of 81 PD participants and 514 eyes of 266 controls.

METHODS

Participants underwent OCT angiography (OCTA) imaging using the Zeiss Cirrus HD-5000 AngioPlex (Carl Zeiss AG). Capillary perfusion density (CPD) and capillary flux index (CFI) were assessed using a 4.5 × 4.5-mm peripapillary scan, and RNFL thickness was assessed using a 200 × 200-μm optic nerve cube OCT scan. Hoehn and Yahr clinical staging for PD was determined by an experienced movement disorders specialist. Generalized estimating equations adjusted for age and sex were used for analysis.

MAIN OUTCOME MEASURES

Differences in RNFL thickness, CPD, and CFI as assessed using multivariable generalized estimating equations between individuals with PD and controls.

RESULTS

After adjustment for age and sex, average CPD (0.446% ± 0.018% vs. 0.439% ± 0.017%, P < 0.001) and CFI (0.434 ± 0.031 vs. 0.426 ± 0.036, P = 0.008) were significantly higher in PD eyes. Average RNFL thickness was similar between groups (PD 89.71 ± 10.45 μm vs. control 88.20 ± 10.33 μm, P = 0.19). Significant correlations between Hoehn and Yahr stage and OCTA parameters were not observed. The OCTA parameters were not significantly different between eyes of the same patient.

CONCLUSIONS

Increased peripapillary microvascular density and flux were detected in a large cohort of individuals with PD compared with controls after adjusting for age and sex; however, RNFL thickness was similar between groups. Peripapillary OCTA parameters may not correlate with the severity of PD. OCTA may serve as a noninvasive method to identify novel biomarkers for the early diagnosis of PD; as such, this methodology deserves further investigation.

Advances in retina imaging as potential biomarkers for early diagnosis of Alzheimer's disease

As the most common form of dementia, Alzheimer’s disease (AD) is characterized by progressive cognitive impairments and constitutes a major social burden. Currently, the invasiveness and high costs of tests have limited the early detection and intervention of the disease. As a unique window of the brain, retinal changes can reflect the pathology of the brain. In this review, we summarize current understanding of retinal structures in AD, mild cognitive impairment (MCI) and preclinical AD, focusing on neurodegeneration and microvascular changes measured using optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) technologies. The literature suggests that the impairment of retinal microvascular network and neural microstructure exists in AD, MCI and even preclinical AD. These findings provide valuable insights into a better understanding of disease pathogenesis and demonstrate that retinal changes are potential biomarkers for early diagnosis of AD and monitoring of disease progression.

Central retina changes in Parkinson's disease: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Central retina imaging is important for early Parkinson's disease (PD) recognition. We aimed to investigate central retina changes using spectral domain-optical coherence tomography (SD-OCT) in PD patients.

METHODS

We systematically searched PubMed and EMBASE to identify studies comparing the whole or individual layer thickness of central retina between PD patients and health controls using SD-OCT from inception to April 25, 2020. Data were extracted at eye level. We pooled the mean difference with random effects model. Subgroup analysis and mete-regression were done to detect possible source of heterogeneity.

RESULTS

We included 27 studies (28 sets of data) enrolling 1470 PD patients (2288 eyes) and 1552 health controls (2524 eyes) in our meta-analysis. Compared with control eyes, the whole thickness of central retina decreased significantly at fovea center by mean difference - 2.70 μm (95% CI [- 4.87, - 0.53], p = 0.01) and in all quadrants in PD eyes. The combination of ganglion cell layer and inner plexiform layer thinned by an average mean difference of - 3.17 μm (95% CI [- 5.07, - 1.26], p = 0.001). The nerve fiber layer thinned by an average mean difference - 0.66 μm (95% CI [- 1.09 to - 0.23], p = 0.003). There was no significant difference in the thickness of inner nuclear layer, outer plexiform layer and outer nuclear layer between eyes of PD and controls. The results of subgroup analysis and mete-regression were consistent.

CONCLUSION

The whole thickness, the thickness of the combination of ganglion cell layer and inner plexiform layer, and nerve fiber layer of central retina decreased significantly in PD patients.

Retinal Thickness Predicts the Risk of Cognitive Decline in Parkinson Disease

Objective

This study was undertaken to analyze longitudinal changes of retinal thickness and their predictive value as biomarkers of disease progression in idiopathic Parkinson's disease (iPD).

Methods

Patients with Lewy body diseases were enrolled and prospectively evaluated at 3 years, including patients with iPD (n = 42), dementia with Lewy bodies (n = 4), E46K‐SNCA mutation carriers (n = 4), and controls (n = 17). All participants underwent Spectralis retinal optical coherence tomography and Montreal Cognitive Assessment, and Unified Parkinson's Disease Rating Scale score was obtained in patients. Macular ganglion cell–inner plexiform layer complex (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thickness reduction rates were estimated with linear mixed models. Risk ratios were calculated to evaluate the association between baseline GCIPL and pRNFL thicknesses and the risk of subsequent cognitive and motor worsening, using clinically meaningful cutoffs.

Results

GCIPL thickness in the parafoveal region (1‐ to 3‐mm ring) presented the largest reduction rate. The annualized atrophy rate was 0.63μm in iPD patients and 0.23μm in controls (p < 0.0001). iPD patients with lower parafoveal GCIPL and pRNFL thickness at baseline presented an increased risk of cognitive decline at 3 years (relative risk [RR] = 3.49, 95% confidence interval [CI] = 1.10–11.1, p = 0.03 and RR = 3.28, 95% CI = 1.03–10.45, p = 0.045, respectively). We did not identify significant associations between retinal thickness and motor deterioration.

Interpretation

Our results provide evidence of the potential use of optical coherence tomography–measured parafoveal GCIPL thickness to monitor neurodegeneration and to predict the risk of cognitive worsening over time in iPD. ANN NEUROL 2021;89:165–176

Optical coherence tomography angiography in neuro-ophthalmology: Current clinical role and future perspectives

Optical coherence tomography angiography (OCTA) is a noninvasive, depth-resolved imaging tool for the appraisement of retinal vascular changes. Since its introduction, the understanding of diabetic retinopathy, age-related macular degeneration, central serous retinopathy, and other diseases has been enriched on many fronts. Its dyeless imaging property maps retinal as well as deeper choroidal vasculature in quick succession with good reproducibility. Hence, it can play an important role in the diagnosis and management of optic nerve-related diseases as well. A detailed literature review for its role in nonarteritic anterior ischemic optic neuropathy, papilledema, optic disc drusen, papillitis, hereditary optic neuropathies, central nervous system diseases, and others highlights its role. The whole spectrum of neuro-ophthalmological diseases shows consistent peripapillary and macular capillary changes with structural and functional correlation. The superficial and deeper retinal and choroidal vasculatures are affected depending on the nature of the disease process. Hence, OCTA positions itself as a useful, noninvasive tool in the armamentarium of a neuro-ophthalmologist in future; however, there are several limitations of the OCTA with respect to its technical abilities in challenging neuro-ophthalmic cases. Therefore, future research should be directed to enhance the technical capabilities of OCTA and to determine the more precise role of it in the prognosis of neuro-ophthalmic diseases.

Optical coherence tomography angiography characteristics of optic disc melanocytoma

Background

Optic disc melanocytoma (ODMC) was a benign pigmented intraocular tumor with the rare potential malignant transformation. This study was designed to evaluate tumor vasculature with optical coherence tomography angiography (OCTA) in ODMC.

Methods

Eyes of healthy individuals in a control group and of patients with ODMC were imaged by OCTA systems operating at 840 nm wavelengths and examined. The main outcome measures were OCTA images, qualitative evaluation of optic disc and tumor vasculature, quantitative vascular density (VD) and perfusion density (PD).

Results

One eye of ten normal volunteers and ten patients with ODMC were imaged. Eyes affected by ODMC as compared to the eyes of the control group (all P < 0.05). The healthy optic disc had radially-oriented vessels within the retina on OCTA. Optic disc melanocytoma was characterized by globular, demonstrated tortuous blood vessels, uneven thickness, and relatively disorganized intratumoral vasculature. The VD and PD within ODMC were significantly higher (12.360% ± 4.175, 0.316% ± 0.119%, P < 0.0001) than in normal optic discs (4.160% ± 2.290, 0.102% ± 0.0, 56%, P < 0.0001). No significant differences were established of the VD and PD in each single measurement zone (P > 0.05) between the ODMC and the control eyes. At 840 nm, OCTA could provide sufficient visualization of the tumor vasculature and better penetration through thicker tumors. The full thickness was visualized even in thicker tumors and highly pigmented lesions (> 2 mm). Interpretable OCTA images were obtained in 96% of the participants in whom imaging was attempted.

Conclusions

OCTA may provide a noninvasive, safe, and efficient technique for evaluating a variety of neoplasms including the growth and vascularity in ODMC. OCTA could facilitate the evaluation of the vascular abnormalities of tumors and the effect of melanin on the penetration of the OCTA beam was not significant.

Combination of optical coherence tomography (OCT) and OCT angiography increases diagnostic efficacy of Parkinson's disease

Background

To assess the diagnostic efficacy of optical coherence tomography (OCT) and OCT angiography (OCTA) in Parkinson's disease (PD).

Methods

OCT was used to obtain macular parameters and peripapillary retinal nerve fiber layer (RNFL) thickness. The macular superficial retinal vessel and foveal avascular zone (FAZ) were quantified with OCTA. The area under the receiver operating characteristic curve (AUC) indicated the diagnostic efficacy of the parameters.

Results

Thirty-five eyes from 35 PD patients and 35 eyes from 35 age-matched healthy subjects who served as controls were evaluated. The mean RNFL thickness overall and the thicknesses of the other three quadrants were similar in PD patients compared with controls (P≥0.358). The RNFL thickness at the temporal quadrant, total macular volume (TMV), macular retinal thickness (MRT), and ganglion cell-inner plexiform layer complex (GCL-IPL) thickness were reduced in the eyes of PD patients (P≤0.046). There was no difference between the CMT of PD patients compared with control subjects (P=0.163). The vessel length density (VLD) in the central, inner and full regions; vessel perfusion density (VPD) in all regions; and the FAZ circularity index in PD patients were significantly lower than in controls (P≤0.049). The AUC of the VLD in PD in the central, inner and full regions were 0.712, 0.728, and 0.650, respectively; The VPD in the central, inner and full region were 0.711, 0.756, and 0.682, respectively. The mean RNFL thickness in the temporal quadrant, TMV and MRT revealed an AUC of 0.718, 0.693 and 0.699, respectively. The VPD in the outer region, FAZ circularity and GCL-IPL thickness did not have diagnostic ability in distinguishing PD from normal eyes (P≥0.05). The AUCs of a combination of the VLD in the inner region and TMV, the VLD in the inner region and MRT, the VPD in the inner region and TMV, and the VPD in the inner region and MRT, were 0.843, 0.849, 0.849, and 0.848, respectively (P≤0.001).

Conclusions

Decreased OCT and OCTA parameters were detected in the eyes of PD patients. Combined non-invasive measurements of OCT and OCTA had better diagnostic ability than either alone, and may provide an additional biomarker for PD progression.

Optical Coherence Tomography Angiography in Neurodegenerative Disorders

Retinal microcirculation shares similar features with cerebral small blood vessels. Thus, the retina may be considered an accessible 'window' to detect the microvascular damage occurring in the setting of neurodegenerative disorders. Optical coherence tomography angiography (OCT-A) is a non-invasive imaging modality providing depth resolved images of blood flow in the retina, choroid, and optic nerve. In this review, we summarize the current literature on the application of OCT-A in glaucoma and central nervous system conditions such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Future directions aiming at evaluating whether OCT-A can be an additional biomarker for the early diagnosis and monitoring of neurodegenerative disorders are also discussed.

Systematic Review on Fractal Dimension of the Retinal Vasculature in Neurodegeneration and Stroke: Assessment of a Potential Biomarker

Introduction: Ocular manifestations in several neurological pathologies accentuate the strong relationship between the eye and the brain. Retinal alterations in particular can serve as surrogates for cerebral changes. Offering a “window to the brain,” the transparent eye enables non-invasive imaging of these changes in retinal structure and vasculature. Fractal dimension (FD) reflects the overall complexity of the retinal vasculature. Changes in FD could reflect subtle changes in the cerebral vasculature that correspond to preclinical stages of neurodegenerative diseases. In this review, the potential of this retinal vessel metric to serve as a biomarker in neurodegeneration and stroke will be explored.

Methods: A literature search was conducted, following the PRISMA Statement 2009 criteria, in four large bibliographic databases (Pubmed, Embase, Web Of Science and Cochrane Library) up to 12 October 2019. Articles have been included based upon their relevance. Wherever possible, level of evidence (LOE) has been assessed by means of the Oxford Centre for Evidence-based Medicine Level of Evidence classification.

Results: Twenty-one studies were included for qualitative synthesis. We performed a narrative synthesis and produced summary tables of findings of included papers because methodological heterogeneity precluded a meta-analysis. A significant association was found between decreased FD and neurodegenerative disease, mainly addressing cognitive impairment (CI) and dementia. In acute, subacute as well as chronic settings, decreased FD seems to be associated with stroke. Differences in FD between subtypes of ischemic stroke remain unclear.

Conclusions: This review provides a summary of the scientific literature regarding the association between retinal FD and neurodegenerative disease and stroke. Central pathology is associated with a decreased FD, as a measure of microvascular network complexity. As retinal FD reflects the global integrity of the cerebral microvasculature, it is an attractive parameter to explore. Despite obvious concerns, mainly due to a lack of methodological standardization, retinal FD remains a promising non-invasive and low-cost diagnostic biomarker for neurodegenerative and cerebrovascular disease. Before FD can be implemented in clinic as a diagnostic biomarker, the research community should strive for uniformization and standardization.