Stereopsis in drug naïve Parkinson's disease patients

Visual Dysfunction in Parkinson's Disease

Non-motor symptoms in Parkinson's disease (PD) include ocular, visuoperceptive, and visuospatial impairments, which can occur as a result of the underlying neurodegenerative process. Ocular impairments can affect various aspects of vision and eye movement. Thus, patients can show dry eyes, blepharospasm, reduced blink rate, saccadic eye movement abnormalities, smooth pursuit deficits, and impaired voluntary and reflexive eye movements. Furthermore, visuoperceptive impairments affect the ability to perceive and recognize visual stimuli accurately, including impaired contrast sensitivity and reduced visual acuity, color discrimination, and object recognition. Visuospatial impairments are also remarkable, including difficulties perceiving and interpreting spatial relationships between objects and difficulties judging distances or navigating through the environment. Moreover, PD patients can present visuospatial attention problems, with difficulties attending to visual stimuli in a spatially organized manner. Moreover, PD patients also show perceptual disturbances affecting their ability to interpret and determine meaning from visual stimuli. And, for instance, visual hallucinations are common in PD patients. Nevertheless, the neurobiological bases of visual-related disorders in PD are complex and not fully understood. This review intends to provide a comprehensive description of visual disturbances in PD, from sensory to perceptual alterations, addressing their neuroanatomical, functional, and neurochemical correlates. Structural changes, particularly in posterior cortical regions, are described, as well as functional alterations, both in cortical and subcortical regions, which are shown in relation to specific neuropsychological results. Similarly, although the involvement of different neurotransmitter systems is controversial, data about neurochemical alterations related to visual impairments are presented, especially dopaminergic, cholinergic, and serotoninergic systems.

Narrative Review Concerning the Clinical Spectrum of Ophthalmological Impairments in Parkinson's Disease

Ophthalmic non-motor impairments are common in Parkinson's disease patients, from the onset of the neurodegenerative disease and even prior to the development of motor symptoms. This is a very crucial component of the potential for early detection of this disease, even in its earliest stages. Since the ophthalmological disease is extensive and impacts all extraocular and intraocular components of the optical analyzer, a competent assessment of it would be beneficial for the patients. Because the retina is an extension of the nervous system and has the same embryonic genesis as the central nervous system, it is helpful to investigate the retinal changes in Parkinson's disease in order to hypothesize insights that may also be applicable to the brain. As a consequence, the detection of these symptoms and signs may improve the medical evaluation of PD and predict the illness' prognosis. Another valuable aspect of this pathology is the fact that the ophthalmological damage contributes significantly to the decrease in the quality of life of patients with Parkinson's disease. We provide an overview of the most significant ophthalmologic impairments associated with Parkinson's disease. These results certainly constitute a large number of the prevalent visual impairments experienced by PD patients.

Regional Metabolic Changes Influencing Three-Dimensional Perception in Parkinson's Disease

Background and Purpose

Stereopsis refers to the perception of depth and awareness of the distance of an object from the observer that results from the brain receiving visual stimuli from both eyes in combination. Patients with idiopathic Parkinson’s disease (PD patients) typically experience problems with vision, eyeball movements, and visual perception due to degeneration of the cells that generate dopamine in the brain. We therefore hypothesized that stereopsis is affected more by visual cortical dysfunction in idiopathic PD than by retina and subcortical structural dysfunction.

Methods

We analyzed stereopsis in 12 PD patients and 7 healthy controls using a three-dimensional (3D) television (TV). Before allowing patients to watch TV, we examined their visual acuity and strabismus using the Titmus Stereo Fly Test, and evaluated their cognitive function using cognitive tests. The patients watched 3D and two-dimensional (2D) versions of a movie with an approximate duration of 17 minutes, and then completed a questionnaire about stereopsis. All subjects underwent brain F-18 fluorodeoxyglucose (FDG) positron-emission tomography after watching the 3D version of the movie. One week later, subjects watched the 2D version of the same movie under the same conditions. Each scan was analyzed using statistical parametric mapping (version 8) software.

Results

The visual cortex was activated less in the PD patients than in the healthy controls when watching the 2D or 3D movie. However, there was no significant difference between watching 2D and 3D movies in the PD patients or healthy controls.

Conclusions

The lower activation of the primary visual cortex in PD patients suggests the presence of dysfunction of the visual cortex. In addition, there was less activation of the visual association cortex in PD patients when watching a 3D movie than in controls under the same conditions. This might be one reason why PD patients do not recognize real and dynamic stereopsis. These findings have clinical significance since they suggest that safety needs to be considered when making devices or programs using 3D or virtual reality for use by patients with various cerebral degenerative diseases.

Stereopsis and Eye Movement Abnormalities in Parkinson’s Disease and Their Clinical Implications

Background

Parkinson’s disease (PD) is not exclusively a motor disorder. Among non-motor features, patients with PD possess sensory visual dysfunctions. Depth perception and oculomotor deficits can significantly impact patients’ motor performance. Stereopsis and eye behavioral study using 3D stimuli may help determine their implications in disease status.

Objective

The objective of this study is to investigate stereopsis and eye movement abnormalities in PD with reliable tools and their correlation with indicators of PD severity. We hypothesize that patients with PD exhibit different eye behaviors and that these differences may correlate to the severity of motor symptoms and cognitive status.

Methods

Control and PD participants were first evaluated for visual acuity, visual field, contrast acuity, and stereo perception with 2D and Titmus stereotests, followed by the assessment with a 3D active shutter system. Eye movement behaviors were assessed by a Tobii X2-60 eye tracker.

Results

Screening visual tests did not reveal any differences between the PD and control groups. With the 3D active shutter system, the PD group demonstrated significantly worse stereopsis. The preserved cognitive function was correlated to a more intact stereo function. Patients with PD had longer visual response times, with a higher number of fixations and bigger saccade amplitude, suggesting fixation stabilization difficulties. Such changes showed a positive correlation with the severity of motor symptoms and a negative correlation with normal cognitive status.

Conclusion

We assessed stereopsis with a 3D active shutter system and oculomotor behaviors with the Tobii eye tracker. Patients with PD exhibit poorer stereopsis and impaired oculomotor behaviors during response time. These deficits were correlated with PD motor and cognitive status. The visual parameters may potentially serve as the clinical biomarkers for PD.

Visual Function and Visual Perception among Senior Citizens with Mild Cognitive Impairment in Taiwan

Purpose: With the benefits of advanced medical technology, Taiwan has gradually changed from an aged society to a super-aged society. According to previous studies, the prevalence rate of mild cognitive impairment (MCI) over the age of 60 is 15% to 20%. Therefore, the main purpose of our study was to analyze the correlation of cognitive function with visual function (specifically, binocular vision and visual perception) in Taiwanese volunteers aged 60 years or older. Methods: Thirty-six healthy participants who were not taking psychiatric medications and who had not been diagnosed with any retinal or optic nerve diseases were enrolled. Addenbrooke’s cognitive examination III (ACE-III), binocular visual function, and visual perception evaluation were performed, and the data analyzed statistically by t-test, χ², linear regression, and MANOVA. Results: Cognitive function was closely correlated with visual function and visual perception; the horizontal adjustment time of binocular eye movement, stereopsis, the motor-free visual perception test-4 (MVPT-4), and peripheral awareness actually displayed higher explanatory power in predicting cognitive function. In addition, various interactive parameters between visual function and visual perception were found to affect specific aspects of ACE-III. Discussion: Our study revealed that there was a close correlation of cognitive function with visual function; as such, it may be possible to predict visual function deficits in patients with mild cognitive impairment.

How I do it: The Neuro-Ophthalmological Assessment in Parkinson's Disease

Visual disorders like double vision, dry eyes, and visual field deficits are common but frequently missed in Parkinson’s disease. Here, we aim to increase awareness for these visual disorders in Parkinson patients by discussing several common problems that can be easily diagnosed using comprehensive history taking and a basic neuro-ophthalmological examination. We offer practical guidance for the patient interview and physical exam that can facilitate a timelier recognition of visual disorders. Such recognition has immediate therapeutic relevance, because Parkinson patients are strongly dependent on an adequate vision, for example to optimally benefit from visual cueing strategies.

Contribution of the GABAergic System to Non-Motor Manifestations in Premotor and Early Stages of Parkinson's Disease

Non-motor symptoms are common in Parkinson’s disease (PD) and they represent a major source of disease burden. Several non-motor manifestations, such as rapid eye movement sleep behavior disorder, olfactory loss, gastrointestinal abnormalities, visual alterations, cognitive and mood disorders, are known to precede the onset of motor signs. Nonetheless, the mechanisms mediating these alterations are poorly understood and probably involve several neurotransmitter systems. The dysregulation of GABAergic system has received little attention in PD, although the spectrum of non-motor symptoms might be linked to this pathway. This Mini Review aims to provide up-to-date information about the involvement of the GABAergic system for explaining non-motor manifestations in early stages of PD. Therefore, special attention is paid to the clinical data derived from patients with isolated REM sleep behavior disorder or drug-naïve patients with PD, as they represent prodromal and early stages of the disease, respectively. This, in combination with animal studies, might help us to understand how the disturbance of the GABAergic system is related to non-motor manifestations of PD.

Visual dysfunction in patients with idiopathic rapid eye movement sleep behavior disorder

OBJECTIVE

Visual dysfunction is a common feature in α-synucleiopathies but rarely assessed in patients with idiopathic rapid eye movement sleep behavior disorder (iRBD). The current study is set to investigate the comprehensive visual function in iRBD as compared to patients of Parkinson's disease (PD) with RBD.

METHODS

Eighty-three iRBD subjects diagnosed with polysomnograph (PSG), 52 early PD patients (Hoehn-Yahr stages<3) with RBD symptom prior to onset of motor symptoms and 79 healthy controls without RBD diagnosed based on RBD Questionnaire-Hong Kong (RBDQ-HK) were enrolled in this study. Visual function including color discrimination, stereopsis function, visual illusion (VI) or hallucination (VH) were assessed in addition to UPDRS, Purdue Pegboard test (PPT) and cognitive tests.

RESULTS

Abnormal color discrimination and stereopsis were presented significantly higher in both iRBD and PD patients as compared to controls and more severe in PD than in iRBD. Color discrimination was decreased in all four color in PD patients but not green color in iRBD subjects. Stereopsis test was abnormal in both iRBD and PD, but the proportion of subjects with abnormal stereopsis was significantly higher in PD patients (69.6% vs 42%). Similar number of subjects with iRBD and PD were presented with illusion but only PD patients reported more hallucination. Changes of visual function were associated with age and cognition in both iRBD and PD subjects but was also affected independently by disease duration and clinical stage or fine motor function in PD. In addition, decreased fine motor function demonstrated by PPT was also observed in some iRBD subjects.

CONCLUSION

Our results demonstrated comprehensively that visual dysfunction was present in iRBD subjects similar but in a less degree of severity to PD patients, and associated with age, cognition and motor deficit. Whether or not it can be useful in predicting iRBD conversion to PD warrants further investigation.

LRRK2-associated Parkinson's disease patients have better stereopsis than idiopathic Parkinson disease

OBJECTIVES

Visual dysfunctions are frequent and have several manifestations in idiopathic Parkinson's disease (PD). However, the characteristics of these complications in LRRK2 (leucine-rich kinase 2)-associated PD patients still lack systematic research. The purpose of this study is to assess visual functions of LRRK2-associated PD patients.

PATIENTS AND METHODS

Twenty-five (25) PD patients with LRRK2 R1628P and G2385R variants were included in the study and compared to 28 PD patients without these variants and 28 age-matched healthy controls. The genotypes of PD patients were kept double-blinded. Information on age, sex, disease duration, the movement disorder society-unified Parkinson's disease rating scale (MDS-UPDRS), Hoehn and Yahr staging scale (H&Y), Mini-Mental Examination (MMSE) and Montreal Cognitive Assessment (MoCA) were included. Visual functions assessment included color perception, contrast sensitivity and stereopsis.

RESULTS

PD patients with or without LRRK2 R1628P and G2385R variants have declined contrast sensitivity, diminished color discrimination and damaged stereopsis. There was no significant difference in retinal level visual deficiency (color discrimination and contrast sensitivity) between PD with LRRK2 variants and those without, but cortex level visual function, i.e. stereopsis is better in PD with LRRK2 variants than non-carrier PD patients. The associated factors of stereopsis are different. The stereopsis is associated with MoCA scores independently in non-carrier PD patients, but with UPDRSIII scores in LRRK2-associated PD patients.

CONCLUSIONS

Visual functions are similarly affected in PD patients with and without LRRK2 R1628P and G2385R variants, but LRRK2-associated PD patients have better stereopsis than idiopathic PD patients.

Neuropathology of Nonmotor Symptoms of Parkinson's Disease

Parkinson's disease (PD), a multiorgan neurodegenerative disorder associated with α-synuclein deposits throughout the nervous system and many organs, is clinically characterized by motor and nonmotor features, many of the latter antedating motor dysfunctions by 20 or more years. The causes of the nonmotor manifestations such as olfactory, autonomic, sensory, neuropsychiatric, visuospatial, sleep, and other disorders are unlikely to be related to single lesions. They are mediated by the involvement of both dopaminergic and nondopaminergic systems, and diverse structures outside the nigrostriatal system that is mainly responsible for the motor features of PD. The nonmotor alterations appear in early/prodromal stages of the disease and its further progression, suggesting a topographical and chronological spread of the lesions. This lends further support for the notion that PD is a multiorgan proteinopathy, although the exact relationship between presymptomatic and later developing nonmotor features of PD and neuropathology awaits further elucidation.

Parkinson's patients can rely on perspective cues to perceive 3D space

3D perception, which is necessary for an optimal navigation in our environment, relies on 2 complementary kinds of cues; binocular cues allowing precise depth localization near the point of visual interest and monocular ones that are necessary for correct global perception of visual space. Recent studies described deficient binocular 3D vision in PD patients; here we tested 3D vision in PD patients when based on monocular cues (m3D). Sixteen PD patients and 16 controls had to categorize visual stimuli as perceived in 2D (flat) or 3D (with depth). Both performance and response times were measured. EEGs were recorded to extract Visual Evoked Potentials. Effects of PD were tested by comparing psychometric and electrophysiological data obtained in controls and PD patients evaluated without dopaminergic treatment. Effects of Levodopa were tested by comparing data in PD patients with and without dopaminergic treatment. We didn't find statistical differences between PD patients and controls' performance. Severity of PD (UPDRS III) in OFF condition is positively correlated with P1 amplitudes and latencies for both 2D and m3D stimuli. Levodopa administration didn't modify either PD patients' performances although it increases principal visual components latencies for both 2D and m3D stimuli. Unlike binocular 3D vision, monocular 3D vision does not seem to get affected by PD. However given the correlation between severity of PD and VEPs' modifications, alteration of visual cortical processing might have nonetheless begun. PD patients reporting trouble in perceiving space must rely more on m3D cues present in the environment.

Nonmotor Symptoms and Cognitive Decline in de novo Parkinson's Disease

BACKGROUND

Cognitive impairments are common in Parkinson's disease (PD). Despite its clinical importance, the development of dementia is still difficult to predict. In this study, we investigated the possible associations between non-motor symptoms and the risk of developing dementia within a 2-year observation period in PD.

METHODS

A total of 80 patients with PD participated in this study. Nonmotor symptoms (the Nonmotor Symptoms Questionnaire), PD status (Unified Parkinson's Disease Rating Scale), depression (Geriatric d Depression Scale or Montgomery-Asberg Depression Scale), stereopsis and severity of nonmotor symptoms (Non-motor symptoms scale) were assessed. Global cognitive function (Mini-Mental State Examination) were evaluated at baseline and 2 years later.

RESULTS

Presence of depression, vivid dreaming, REM sleep behavior disorders, hyposmia, abnormal stereopsis, non-smoking and postural instability/ gait disturbance phenotype were associated with a significantly more rapid decline of Mini-Mental State Examination. Logistic regression analyses demonstrated that depression (odds ratio=13.895), abnormal stereopsis (odds ratio=10.729), vivid dreaming (odds ratio=4.16), REM sleep behavior disorders (odds ratio=5.353) and hyposmia (odds ratio=4.911) were significant independent predictors of dementia risk within 2 years. Postural instability/ gait disturbance phenotype and age >62 years were also independent predictors of dementia risk (odd ratio=38.333, odds ratio=10.625).

CONCLUSIONS

We suggest that depression, vivid dreaming, REM sleep behavior disorders, hyposmia and abnormal stereopsis are closely associated with cognitive decline, and that presence of these nonmotor symptoms predict the subsequent development of Parkinson's disease dementia.

Gait in Parkinson's disease: A visuo-cognitive challenge

Vision and cognition have both been related to gait impairment in Parkinson's disease (PD) through separate strands of research. The cumulative and interactive effect of both (which we term visuo-cognition) has not been previously investigated and little is known about the influence of cognition on vision with respect to gait. Understanding the role of vision, cognition and visuo-cognition in gait in PD is critical for data interpretation and to infer and test underlying mechanisms. The purpose of this comprehensive narrative review was to examine the interdependent and interactive role of cognition and vision in gait in PD and older adults. Evidence from a broad range of research disciplines was reviewed and summarised. A key finding was that attention appears to play a pivotal role in mediating gait, cognition and vision, and should be considered emphatically in future research in this field.

The range and nature of non-motor symptoms in drug-naive Parkinson's disease patients: a state-of-the-art systematic review

Non-motor symptoms (NMS) are a key component of Parkinson’s disease (PD). A range of NMS, most notably impaired sense of smell, sleep dysfunction, and dysautonomia are present from the ‘pre-motor’ phase to the final palliative stage. Theories as to the pathogenesis of PD such as those proposed by Braak and others also support the occurrence of NMS in PD years before motor symptoms start. However, research addressing the range and nature of NMS in PD has been confounded by the fact that many NMS arise as part of drug-related side effects. Thus, drug-naive PD (DNPD) patients provide an ideal population to study the differences in the presentation of NMS. The aim of this paper is therefore to systematically review all the available studies of NMS in DNPD patients. We believe this is the first review of its kind. The current review confirms the increasing research being conducted into NMS in DNPD patients as well as the necessity for further investigation into less-studied NMS, such as pain. Moreover, the data confirms non-motor heterogeneity among PD patients, and, therefore, further research into the concept of non-motor subtyping is encouraged. The review suggests that the clinical assessment of NMS should be integral to any assessment of PD in clinical and research settings.

Many Faces of Parkinson's Disease: Non-Motor Symptoms of Parkinson's Disease

Parkinson’s disease (PD) is a multi-systemic disorder that is characterized by a combination of motor and non-motor symptoms (NMS). The dopaminergic neurodegeneration of PD is involved in the genesis of NMS, but other conditions and side effects of levodopa are also associated with NMS. NMS can develop at all stage of PD and rapid eyeball movement sleep behavior disorder (RBD), constipation, depression, and olfactory dysfunction are considered prodromal signs of PD. Many NMS related with motor deficits and cognitive dysfunction. Some NMS including olfactory dysfunction, RBD and abnormal stereopsis are associated with presence of other NMS of PD. In addition, several NMS can be helpful to differentiate between idiopathic PD and other parkinsonian disorders. Early recognition and management of NMS in PD patients is important for preserving quality of life.

Cognitive functions and stereopsis in patients with Parkinson's disease and Alzheimer's disease using 3-dimensional television: a case controlled trial

Stereopsis or depth perception is an awareness of the distances of objects from the observer, and binocular disparity is a necessary component of recognizing objects through stereopsis. In the past studies, patients with neurodegenerative disease (Alzheimer dementia, AD; Parkinson’s disease IPD) have problems of stereopsis but they did not have actual stimulation of stereopsis. Therefore in this study, we used a 3-dimensional (3D) movie on 3D television (TV) for actual stereopsis stimulation. We propose research through analyzing differences between the three groups (AD, IPD, and Controls), and identified relations between the results from the Titmus Stereo Fly Test, and the 3D TV test. The study also looked into factors that affect the 3D TV test. Before allowing the patients to watch TV, we examined Titmus stereo Fly Test and cognitive test. We used the 3D version of a movie, of 17 minutes 1 second duration, and carried out a questionnaire about stereopsis. The scores of the stereopsis questionnaire were decreased in AD patients, compared with in IPD and controls, although they did not have any difference of Titmus Stereo Fly Test scores. In IPD patients, cognitive function (Montreal cognitive assessment, MoCA) scores were correlated with the scores of the stereopsis questionnaire. We could conclude that Titmus fly test could not distinguish between the three groups and cognitive dysfunction contributes to actual stereopsis perception in IPD patients. Therefore the 3D TV test of AD and IPD patients was more effective than Titmus fly test.

Stereopsis impairment is associated with decreased color perception and worse motor performance in Parkinson's disease

BACKGROUND

We conducted this study is to investigate the correlation between stereopsis dysfunction and color perception, as well as whether stereopsis impairment is associated with motor dysfunction in patients with Parkinson's disease (PD).

METHOD

Our present study included 45 PD patients and 50 non-PD control patients attending the Movement Disorder Center at Xuanwu Hospital Capital Medical University in Beijing from July 2011 to November 2011. Neurologic evaluations and visual function assessments were conducted, and the results between two groups of patients were compared.

RESULTS

We found that the total error scores (TESs) and partial error scores (PESs) for red, green, blue and purple were all significantly higher in PD patients than in control patients. The limited grade on the FLY Stereo Acuity Test with LEA Symbols was significantly lower in PD patients than in control patients (P = 0.0001), whereas the percentage of abnormal stereopsis in PD patients was significantly higher than in control patients (42.2% vs. 12%; P = 0.001). Multiple linear regression analysis showed that PD patients with higher Hoehn and Yahr Scale stage, and those with decreased stereopsis had higher Unified Parkinson's Disease Rating Scale (UPDRS) motor scores and worse motor function. Furthermore, our study demonstrates that the UPDRS motor scores and total average number of the Purdue Pegboard Test scores of PD patients were significantly improved when they had taken their medications, and the TESs and PESs for green were lower in when they were off their medications.

CONCLUSION

Our results provide more information on the underlying mechanisms of vision, motor and stereopsis impairments in PD patients.

Stereopsis and extrastriate cortical atrophy in Parkinson's disease: a voxel-based morphometric study

Among the various visuospatial dysfunctions, deficits of stereopsis could be associated with Parkinson's disease. We examined differences in regional gray matter volume between Parkinson's disease patients with normal stereopsis and with abnormal stereopsis to delineate the possible anatomical correlate of stereopsis. Stereopsis was assessed using the Titmus test in 35 drug-naive patients with Parkinson's disease. Voxel-based morphometry was utilized to assess regionally specific differences in gray matter volume between 16 patients with normal stereopsis and 19 patients with abnormal stereopsis. Patients with abnormal stereopsis had a significant gray matter volume reduction in the right extrastriate visual cortex compared with patients with normal stereopsis (P<0.05, corrected for multiple comparisons). Voxel values extracted from the significant cluster in group comparison were negatively correlated with log seconds of arc of the Titmus test (Spearman correlation, P<0.001). Our results suggest that deficits of stereopsis are associated with nondominant extrastriate cortical atrophy and that abnormal stereopsis implicates the cortical visual dysfunction as part of the nonmotor symptoms in Parkinson's disease.