Lack of association of morphologic and functional retinal changes with motor and non-motor symptoms severity in Parkinson’s disease

Evaluation of Retinal Nerve Fibre Layer Thickness and Choroidal Thickness in Parkinson Disease Patients

To evaluate the retinal nerve fibre layer (RNFL) thickness and choroidal thickness (CT) in Parkinson disease (PD) patients. A comparative cross-sectional, hospital-based study. 39 PD and 39 controls were recruited, who were gender and age matched. Subjects that fulfilled the inclusion criteria underwent optical coherence tomography for evaluation of RNFL thickness and choroidal thickness (CT). There was significant reduction of RNFL thickness in average (adjusted mean 88.87 µm vs. 94.82 µm, P=0.001), superior (adjusted mean 110.08 µm vs. 119.10 µm, P=0.002) and temporal (adjusted mean 63.77 µm vs. 70.36 µm, P=0.004) in PD compared to controls. The central subfoveal CT was significantly thinner in PD compared to controls (adjusted mean 271.13 µm vs. 285.10 µm, P=0.003). In PD group, there was significant weak negative correlation between the duration of PD with average RNFL thickness (r=-0.354, P=0.027), moderate negative correlation between the duration of PD with central subfoveal CT (r=-0.493, P=0.001), and weak negative correlation between the stage of PD with central subfoveal CT (r=-0.380, P=0.017). PD group had significant thinner average, superior and temporal RNFL thickness and CT compared to controls.

Evaluation of the visual system with visual evoked potential and optical coherence tomography in patients with idiopathic Parkinson's disease and with multiple system atrophy

BACKGROUND

In addition to motor findings, non-motor findings including alterations in visual acuity, decrease in blink reflex, and pupil reactivity cause the impaired quality of life in idiopathic Parkinson's disease (PD) and multiple system atrophy (MSA). Our study aimed to examine possible latency and amplitude changes in pattern visual evoked potentials (pVEP) along with retinal and macular changes in optical coherence tomography (OCT) in PD and MSA groups. We also intended to investigate whether any OCT parameters could be a biomarker for Parkinson's or MSA.

METHODS

Our study included 50 patients with PD, 15 with MSA, and 50 healthy control subjects. All patients in the study underwent neurological and ophthalmological examination and investigations of OCT to measure the retinal and macular thickness and pVEP to assess visual pathways.

RESULTS

When PD, MSA, and control groups were compared, a significant difference was found in all retinal thickness values in average, nasal, and superior retinal nerve fiber thickness (pRNFL), and in all macular thickness values except nasal outer and inferior outer quadrants and in ganglion cell complex (GCC) thicknesses (p < 0.05). Moreover, a significant difference was found in N75, P100, and N145 latencies and N75-P100 amplitude (p < 0.05). The thickness of both pRNFL, inner and outer macular quadrants, was thinner in the MSA group than in PD but GCC thickness was thinner in PD group.

CONCLUSIONS

The present study compared pVEP and OCT parameters in PD and MSA groups. It was concluded that pVEP and OCT examinations were of importance in that they were easily accessible, affordable, noninvasive biomarkers that might be used in early periods and progression of the disease and in follow-up.

Self-Reported Visual Complaints in People with Parkinson’s Disease: A Systematic Review

Background:

Scientific research increasingly focuses on visual symptoms of people with Parkinson’s disease (PD). However, this mostly involves functional measures, whereas self-reported data are equally important for guiding clinical care.

Objective:

This review provides an overview of the nature and prevalence of self-reported visual complaints by people with PD, compared to healthy controls.

Methods:

A systematic literature search was performed. Studies from three databases (PubMed, PsycInfo, and Web of Science) were screened for eligibility. Only studies that reported results of visual self-reports in people with idiopathic PD were included.

Results:

One hundred and thirty-nine eligible articles were analyzed. Visual complaints ranged from function-related complaints (e.g., blurred vision, double vision, increased sensitivity to light or changes in contrast sensitivity) to activity-related complaints (e.g., difficulty reading, reaching, or driving). Visual complaints were more prevalent in people with PD compared to healthy controls. The presence of visual complaints leads to a reduced quality of life (QoL). Increased prevalence and severity of visual complaints in people with PD are related to longer disease duration, higher disease severity, and off-state.

Conclusion:

A large proportion of people with PD have visual complaints, which negatively affect QoL. Complaints are diverse in nature, and specific and active questioning by clinicians is advised to foster timely recognition, acknowledgement, and management of these complaints.

Multimodal brain and retinal imaging of dopaminergic degeneration in Parkinson disease

Parkinson disease (PD) is a progressive disorder characterized by dopaminergic neurodegeneration in the brain. The development of parkinsonism is preceded by a long prodromal phase, and >50% of dopaminergic neurons can be lost from the substantia nigra by the time of the initial diagnosis. Therefore, validation of in vivo imaging biomarkers for early diagnosis and monitoring of disease progression is essential for future therapeutic developments. PET and single-photon emission CT targeting the presynaptic terminals of dopaminergic neurons can be used for early diagnosis by detecting axonal degeneration in the striatum. However, these techniques poorly differentiate atypical parkinsonian syndromes from PD, and their availability is limited in clinical settings. Advanced MRI in which pathological changes in the substantia nigra are visualized with diffusion, iron-sensitive susceptibility and neuromelanin-sensitive sequences potentially represents a more accessible imaging tool. Although these techniques can visualize the classic degenerative changes in PD, they might be insufficient for phenotyping or prognostication of heterogeneous aspects of PD resulting from extranigral pathologies. The retina is an emerging imaging target owing to its pathological involvement early in PD, which correlates with brain pathology. Retinal optical coherence tomography (OCT) is a non-invasive technique to visualize structural changes in the retina. Progressive parafoveal thinning and fovea avascular zone remodelling, as revealed by OCT, provide potential biomarkers for early diagnosis and prognostication in PD. As we discuss in this Review, multimodal imaging of the substantia nigra and retina is a promising tool to aid diagnosis and management of PD.

Optical coherence tomography in patients with Parkinson’s disease

Background

The changes in the different retinal layers in Parkinson’s disease (PD) patients can be easily assessed using optical coherence tomography (OCT). Our aim was to evaluate retinal structural changes in patients with PD using OCT. Structural measurements of the retinal nerve fiber layer (RNFL), macular and ganglion cell complex (GCC) thicknesses were obtained using spectral domain optical coherence tomography. Disease severity was assessed using Unified Parkinson Disease Rating Scale (UPDRS).

Results

Retinal nerve fiber layer parameters, except for the superonasal and inferonasal quadrants, were significantly reduced in PD patients compared to controls. All macular parameters and GCC thickness were also reduced in PD patients compared to controls. Hoehn and Yahr (HY) staging was inversely correlated with all macular parameters, GCC and temporal RNFL thicknesses. UPDRS score showed a significant negative correlation with macular volume, inferior and nasal parafoveal thicknesses, nasal and temporal RNFL thicknesses and GCC thickness. The disease duration was inversely correlated with macular volume, inferior and temporal parafoveal thicknesses and GCC thickness. Using the multivariate linear regression analysis, the HY scale was a significant predictor for both the average GCC thickness and the macular volume. The sensitivity and specificity of average GCC thickness and macular volume to detect disease severity were 58.8%, 86.7%, 64.7% and 86.7%, respectively.

Conclusion

Parkinson’s disease causes axonal damage in the RNFL along with retinal thinning that can be detected using SD-OCT. Patients with greater axonal damage tend to have longer duration of the disease and more severe PD symptoms.

Does retina play a role in Parkinson's Disease?

Visual disorder is one of the non-motor symptoms found in Parkinson's disease (PD). It can be easily identified in the early stages even before the spread of pathological conditions to the brain parts. Studies have revealed that loss of dopamine (DA) cells in retinal layers is a prime cause for both retinal disturbance and pathological conditions of PD. This reduction of DA in retina is due to the aggregation of phosphorylated α-synuclein (aSyn) in the intra-retinal region, which eventually results in visual impairment in PD. Until now, very limited studies have been focused on the mechanism of aSyn influence and DA depletion as a cause for both retinal layer dysfunction and PD. Thus, more research is warranted to provide the missing connection between the exact role of DA and aSyn as a risk factor for visual problems in PD. Hence, the current review's focus is on the function and effects of DA degeneration in retinal cells of PD. Further, we suggest that iron plays a major role in regulating the aggregation of aSyn in the DA cells of retina and brain in PD. The study finds that the unidentified pathophysiological role of retinal degeneration in PD is an essential biomarker that needs further investigation to use it as a novel therapy in treating retinal dysfunctions in PD.

Meta-Analysis of Visual Evoked Potential and Parkinson's Disease

BACKGROUND

Previous studies suggested that visual evoked potential (VEP) was impaired in patients with Parkinson's disease (PD), but the results were inconsistent.

METHODS

We conducted a systematic review and meta-analysis to explore whether the VEP was significantly different between PD patients and healthy controls. Case-control studies of PD were selected through an electronic search of the databases PubMed, Embase, and the Cochrane Central Register of Controlled Trials. We calculated the pooled weighted mean differences (WMDs) and 95% confidence intervals (CIs) between individuals with PD and controls using the random-effects model.

RESULTS

Twenty case-control studies which met our inclusion criteria were included in the final meta-analysis. We found that the P100 latency in PD was significantly higher compared with healthy controls (pooled WMD = 6.04, 95% CI: 2.73 to 9.35, P=0.0003, n=20). However, the difference in the mean amplitude of P100 was not significant between the two groups (pooled WMD = 0.64, 95% CI: -0.06 to 1.33, P=0.07) based on 10 studies with the P100 amplitude values available.

CONCLUSIONS

The higher P100 latency of VEP was observed in PD patients, relative to healthy controls. Our findings suggest that electrophysiological changes and functional defect in the visual pathway of PD patients are important to our understanding of the pathophysiology of visual involvement in PD.

Patterns of Retinal Ganglion Cell Damage in Neurodegenerative Disorders: Parvocellular vs Magnocellular Degeneration in Optical Coherence Tomography Studies

Many neurodegenerative disorders, such as Parkinson’s disease (PD) and Alzheimer’s disease (AD), are characterized by loss of retinal ganglion cells (RGCs) as part of the neurodegenerative process. Optical coherence tomography (OCT) studies demonstrated variable degree of optic atrophy in these diseases. However, the pattern of degenerative changes affecting the optic nerve (ON) can be different. In particular, neurodegeneration is more evident for magnocellular RGCs in AD and multiple system atrophy with a pattern resembling glaucoma. Conversely, in PD and Huntington’s disease, the parvocellular RGCs are more vulnerable. This latter pattern closely resembles that of mitochondrial optic neuropathies, possibly pointing to similar pathogenic mechanisms. In this review, the currently available evidences on OCT findings in these neurodegenerative disorders are summarized with particular emphasis on the different pattern of RGC loss. The ON degeneration could become a validated biomarker of the disease, which may turn useful to follow natural history and possibly assess therapeutic efficacy.

Retinal biomarkers provide "insight" into cortical pharmacology and disease

The retina is an easily accessible out-pouching of the central nervous system (CNS) and thus lends itself to being a biomarker of the brain. More specifically, the presence of neuronal, vascular and blood-neural barrier parallels in the eye and brain coupled with fast and inexpensive methods to quantify retinal changes make ocular biomarkers an attractive option. This includes its utility as a biomarker for a number of cerebrovascular diseases as well as a drug pharmacology and safety biomarker for the CNS. It is a rapidly emerging field, with some areas well established, such as stroke risk and multiple sclerosis, whereas others are still in development (Alzheimer's, Parkinson's, psychological disease and cortical diabetic dysfunction). The current applications and future potential of retinal biomarkers, including potential ways to improve their sensitivity and specificity are discussed. This review summarises the existing literature and provides a perspective on the strength of current retinal biomarkers and their future potential.

A combination of retinal morphology and visual electrophysiology testing increases diagnostic yield in Parkinson's disease

BACKGROUND

Impaired vision and remodeled foveal pit have been demonstrated in Parkinson's disease (PD) patients using different techniques.

METHODS

Ten PD (20 eyes) and eight healthy controls (HC) subjects (16 eyes) were enrolled. Subjects were evaluated for N70 and P100 latencies using two-channel VEP with pattern reversal and on/off pattern; Contrast sensitivity (CS) using Pelli-Robson chart; macular thickness measured using Zeiss-HD optical coherence tomography (OCT).

RESULTS

PD patients had a significantly delayed N70 (reversal pattern) and P100 (on/off pattern), lower CS score, and decreased retinal thickness at temporal 1.5-2.5 mm from the foveola. N70 latency was negatively correlated with CS (R = -0.419, P = 0.01) and average GCL-IPL thickness (R = -0.529, P = 0.001). CS was positively correlated with parafoveal thickness (R = 0.490, P = 0.002). A combination of parafoveal thickness and CS score yielded an AUC of 0.784 for PD discrimination which increased to 0.844 when combined with N70 and P100 measures.

CONCLUSION

A combination of pattern reversal VEP latency, CS score, and inner retinal foveal thickness measures has a high diagnostic yield for PD.