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

Progression of Retinal Ganglion Cell and Nerve Fiber Layer Loss in Spinocerebellar Ataxia 3 Patients

Spectral domain optical coherence tomography (SD-OCT) allows noninvasive measurements of retinal neuron layers. Here, we evaluate the relationship between clinical features and anatomical SD-OCT measurements in patients with spinocerebellar ataxia type 3 (SCA3) and how they change with time. A retrospective review was conducted on SCA3 patients. Clinical variables such as disease duration, number of CAG repeats, and the Scale for the Assessment and Rating of Ataxia (SARA) score were correlated with SD-OCT measurements, including retinal nerve fiber layer (RNFL) thickness, ganglion cell complex (GCC) thickness, macular volume (MV), and central macular thickness (CMT). Seventeen SCA3 patients with an average follow-up of 44.9 months were recruited. Clinical features with significant baseline correlations with SD-OCT measurements included disease duration (CMT r =  - 0.590; GCC r =  - 0.585), SARA score (CMT r =  - 0.560; RNFL r =  - 0.390), and number of CAG repeats (MV r =  - 0.552; RNFL r =  - 0.503; GCC r =  - 0.493). The annual rate of change of the SARA score during follow-up was associated with that of both the MV (r =  - 0.494; p = 0.005) and GCC thickness (r =  - 0.454; p = 0.012). High disability (stages 2 and 3) was independently inversely associated with the annual change in MV (ß coefficient - 17.09; p = 0.025). This study provides evidence of an association between clinical features and objective anatomical measurements obtained by SD-OCT in SCA3 patients. MV and GCC thickness could serve as potential biomarkers of disease severity, as their rates of decrease seem to be related to a worsening in the SARA score. These findings highlight the potential of SD-OCT as a noninvasive tool for assessing disease severity and progression in SCA3 patients.

Distinct retinal reflectance spectra from retinal hyperspectral imaging in Parkinson's disease

BACKGROUND

Recent developments in the retinal hyperspectral imaging method have indicated its potential in addressing challenges posed by neurodegenerative disorders, such as Alzheimer's disease. This human clinical study is the first to assess reflectance spectra obtained from this imaging as a tool for diagnosing patients with Parkinson's disease (PD).

METHODS

Retinal hyperspectral imaging was conducted on a total of 40 participants, including 20 patients with PD and 20 controls. Following preprocessing, retinal reflectance spectra were computed for the macular retina defined by four rectangular regions. Linear discriminant analysis classifiers underwent training to discern patients with PD from control participants. To assess the performance of the selected features, nested leave-one-out cross-validation was employed using machine learning. The indicated values include the area under the curve (AUC) and the corresponding 95% confidence interval (CI).

RESULTS

Retinal reflectance spectra of PD patients exhibited variations in the spectral regions, particularly at shorter wavelengths (superonasal retina, wavelength < 490 nm; inferonasal retina, wavelength < 510 nm) when compared to those of controls. Retinal reflectance spectra yielded an AUC of 0.60 (95% CI: 0.43-0.78) and 0.60 (95% CI: 0.43-0.78) for the superonasal and inferonasal retina, respectively, distinguishing individuals with and without PD.

CONCLUSION

Reflectance spectra obtained from retinal hyperspectral imaging tended to decrease at shorter wavelengths across a broad spectral range in PD patients. Further investigations building upon these preliminary findings are imperative to focus on the retinal spectral signatures associated with PD pathological hallmarks, including α-synuclein.

Neurodegeneration with Brain Iron Accumulation Disorders and Retinal Neurovascular Structure

BACKGROUND

The unique neurovascular structure of the retina has provided an opportunity to observe brain pathology in many neurological disorders. However, such studies on neurodegeneration with brain iron accumulation (NBIA) disorders are lacking.

OBJECTIVES

To investigate NBIA's neurological and ophthalmological manifestations.

METHODS

This cross-sectional study was conducted on genetically confirmed NBIA patients and an age-gender-matched control group. The thickness of retinal layers, central choroidal thickness (CCT), and capillary plexus densities were measured by spectral domain-optical coherence tomography (SD-OCT) and OCT angiography, respectively. The patients also underwent funduscopy, electroretinography (ERG), visual evoked potential (VEP), and neurological examination (Pantothenate-Kinase Associated Neurodegeneration-Disease Rating Scale [PKAN-DRS]). The generalized estimating equation model was used to consider inter-eye correlations.

RESULTS

Seventy-four patients' and 80 controls' eyes were analyzed. Patients had significantly decreased visual acuity, reduced inner or outer sectors of almost all evaluated layers, increased CCT, and decreased vessel densities, with abnormal VEP and ERG in 32.4% and 45.9%, respectively. There were correlations between visual acuity and temporal peripapillary nerve fiber layer (positive) and between PKAN-DRS score and disease duration (negative), and scotopic b-wave amplitudes (positive). When considering only the PKAN eyes, ONL was among the significantly decreased retinal layers, with no differences in retinal vessel densities. Evidence of pachychoroid was only seen in patients with Kufor Rakeb syndrome.

CONCLUSION

Observing pathologic structural and functional neurovascular changes in NBIA patients may provide an opportunity to elucidate the underlying mechanisms and differential retinal biomarkers in NBIA subtypes in further investigations. © 2023 International Parkinson and Movement Disorder Society.

Retinal Alterations Predict Early Prodromal Signs of Neurodegenerative Disease

Neurodegenerative diseases are an increasingly common group of diseases that occur late in life with a significant impact on personal, family, and economic life. Among these, Alzheimer's disease (AD) and Parkinson's disease (PD) are the major disorders that lead to mild to severe cognitive and physical impairment and dementia. Interestingly, those diseases may show onset of prodromal symptoms early after middle age. Commonly, the evaluation of these neurodegenerative diseases is based on the detection of biomarkers, where functional and structural magnetic resonance imaging (MRI) have shown a central role in revealing early or prodromal phases, although it can be expensive, time-consuming, and not always available. The aforementioned diseases have a common impact on the visual system due to the pathophysiological mechanisms shared between the eye and the brain. In Parkinson's disease, α-synuclein deposition in the retinal cells, as well as in dopaminergic neurons of the substantia nigra, alters the visual cortex and retinal function, resulting in modifications to the visual field. Similarly, the visual cortex is modified by the neurofibrillary tangles and neuritic amyloid β plaques typically seen in the Alzheimer's disease brain, and this may reflect the accumulation of these biomarkers in the retina during the early stages of the disease, as seen in postmortem retinas of AD patients. In this light, the ophthalmic evaluation of retinal neurodegeneration could become a cost-effective method for the early diagnosis of those diseases, overcoming the limitations of functional and structural imaging of the deep brain. This analysis is commonly used in ophthalmic practice, and interest in it has risen in recent years. This review will discuss the relationship between Alzheimer's disease and Parkinson's disease with retinal degeneration, highlighting how retinal analysis may represent a noninvasive and straightforward method for the early diagnosis of these neurodegenerative diseases.

Imaging Biomarkers in Prodromal and Earliest Phases of Parkinson's Disease

Assessing imaging biomarker in the prodromal and early phases of Parkinson's disease (PD) is of great importance to ensure an early and safe diagnosis. In the last decades, imaging modalities advanced and are now able to assess many different aspects of neurodegeneration in PD. MRI sequences can measure iron content or neuromelanin. Apart from SPECT imaging with Ioflupane, more specific PET tracers to assess degeneration of the dopaminergic system are available. Furthermore, metabolic PET patterns can be used to anticipate a phenoconversion from prodromal PD to manifest PD. In this regard, it is worth mentioning that PET imaging of inflammation will gain significance. Molecular imaging of neurotransmitters like serotonin, noradrenaline and acetylcholine shed more light on non-motor symptoms. Outside of the brain, molecular imaging of the heart and gut is used to measure PD-related degeneration of the autonomous nervous system. Moreover, optical coherence tomography can noninvasively detect degeneration of retinal fibers as a potential biomarker in PD. In this review, we describe these state-of-the-art imaging modalities in early and prodromal PD and point out in how far these techniques can and will be used in the future to pave the way towards a biomarker-based staging of PD.

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.

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.