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Deciphering Parkinson’s Disease through Eye Movements: A 
Promising Tool for Early Diagnosis in the Face of 

Cognitive Impairment 
 

B.Buvana, R .Chaithu, N . Samyoutha  
 

Assistant Professor1,2,3, Badruka Pharmacy College and Institution 

 

 

 

 
 

1. Introduction 
According to [1], the frequency of Parkinson's disease 

(PD) is expected to double by 2030, impacting over 1% of 

the population aged 65 and over. It is the second most 

frequent neurodegenerative ailment. Cognitive 

impairment is a significant nonmotor symptom of 

Parkinson's disease (PD) that may develop at any point in 

the disease progression, even before motor symptoms 

appear. It has a profound effect on patients' ability to carry 

out daily tasks and interact socially. 

raises the emotional and financial strain on families and 

communities as a whole, as well as on carers individually. 

A wide range of cognitive dysfunctions, including issues 

with attention, memory, visual space, language function, 

and executive function, may characterise Parkinson's 

disease dementia (PDD) [2]. Individuals with PDD have 

more severe forms of attention deficit, decreased 

executive function, and visual impairments when 

compared to those with Alzheimer's disease (AD).  

 

spatial function, with little impairment to linguistic 

function [3]. Additionally, compared to individuals with 

normal cognition, those with cognitive impairment have 

much reduced quality-of-life and activities of daily living. 

However, there is currently fewer research and therapy 

options available for nonmotor symptoms of PD, 

particularly cognitive impairment, compared to motor 

symptoms. According to epidemiological survey data, the 

occurrence of cognitive impairment is 2.5-6 times greater 

in PD patients compared to non-PD patients of the same 

age group [4]. The pace of cognitive decline, the regions of 

the brain affected, and the severity of the disease may vary 

greatly; it can begin before a PD diagnosis, continue 

throughout the diagnosis, or manifest years or even decades 

after the diagnosis [5]. After twenty years of illness, the 

cumulative incidence of PDD might approach 80% [6], 

which becomes a major predictor with age [7]. Cognitively 

Abstract— At any point in the progression of Parkinson's disease (PD), cognitive impairment becomes the most 

prominent and prevalent nonmotor symptom. Unfortunately, reliable biomarkers for assessing cognitive impairment and 

disease development, particularly in its early stages, are currently lacking. The cognitive scale is now the gold standard for 
PD patients' cognitive evaluations, although it has limited sensitivity and accuracy, particularly when it comes to detecting 

moderate cognitive impairment in its early stages. One of the most effective ways to learn about the connection between 

behaviour and brain processes is to use eye movement tracking, a cutting-edge neurophysiological monitoring tool. 

Researchers have recently discovered that eye movement monitoring may be used as a less cognitive and nonverbal way to 
assess the progression of illness in people with cognitive impairment. Patients with PD may have their cognitive state, illness 

severity, and disease progression monitored using eye movement monitoring, since it has a strong association with the 

standard cognitive evaluation scale. The instrument's detection of eye movement is more objective and repeatable than the 

conventional cognitive scale. According to previous research, one of the most prominent forms of cognitive dysfunction in 
PD patients is executive dysfunction, which is associated with increased saccade error rate, increased disinhibition on the 

delayed saccade task, and prolonged saccade reaction time. This provides further evidence that measuring eye movement is 

useful for PD diagnosis, tracking the illness's development, making differential diagnoses, and maybe even foretelling how 

the disease would affect people with both PD and cognitive impairment. This article provides a synopsis of the literature on 
the link between PD and EMD in terms of cognitive impairment. 



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impaired PD patients are more likely to have dyskinesia 

progression and a poor prognosis, both of which 

complicate PD diagnosis.  

When diagnosing and differentiating nervous system 

diseases, including neurodegenerative motor disorders 

like α-synuclein (α-syn) disease (including PD, dementia 

with Lewy bodies (DLB), and multiple system atrophy 

(MSA)) and tauopathies (progressive supranuclear 

paralysis, PSP)) [8, 9], the neurological physical 

examination of eye movement function is crucial. A 

decreased saccade amplitude, prolonged saccade latency, 

and special saccade mode have been proposed in recent 

research on eye movement in PD [9, 10]. These features 

may be significant in the early detection, development, 

and differential diagnosis of PD cognitive impairment, as 

well as in the course of the disease itself.  

2. Pathogenesis of Cognitive Impairment in PD 

 

Our understanding of the neuropathological process 

underlying PDD is lacking. Research has shown a 

correlation between the degree of cognitive impairment in 

PD patients and the pathological deposition of α-syn in the 

form of the cortical Lewy body (LB) [11]. A lack of 

dopaminergic (DA) neurons in the striatum caused by the 

loss of substantia nigra neurons is one of the main 

pathological features. Another is the buildup of α-

synaptophysin in the inclusion bodies of neurons, which 

first manifests in cholinergic and monoaminergic brain 

stem neurons and the olfactory system, resulting in 

notable synaptic lesions [12]. PDD and DLB are on 

opposite extremities of the illness continuum, however 

they share many clinical features. Although they are often 

seen as opposite extremities of the illness spectrum, DLB 

and PDD have strong links with α-syn and share a lot of 

common clinical symptoms. The brainstem and cortical 

catecholaminergic, DA, and noradrenergic nuclei are 

more susceptible to the disease and degradation of α-syn 

in PD and DLB [13]. Defects in cognition and 

neuropsychiatry are thought to result from these illnesses' 

loss of monoaminergic neurons [14]. The substantia nigra, 

amygdala, brain, and hippocampal CA2 region are areas 

where α-syn lesions may be discovered in pigment 

neurons. The  

 

α-syn pathology was found to be significantly correlated 

with an increase in activated microglia at the front of the 

amygdala, a progressive reduction in α-syn pathology 

from the anterior pericortical granules to the intermediate 

granule abnormal subregions and the posterior cortical 

granule island subregions [15, 16]. Mild cognitive 

impairment (PD-MCI) is characterised by a dispersion of 

DA neuronal defects in the caudate nucleus; in PDD, these 

defects spread to the periphery and neocortical regions. 

According to references [17, 18], the primary factor that 

determines PDD and DLB is the penetration of α-syn into 

the marginal zone (also known as the parahippocampal 

region) and neocortical area (also known as the frontal and 

temporal lobe binding area). There is substantial variation 

in PD pathology, according to a longterm clinical 

pathology research by Molly et al. [19]. Various cognitive 

domains may lean towards various degenerative patterns. 

Further factors that contribute to the development of PD 

include oxidative stress, mitochondrial dysfunction, 

cellular calcium imbalance, neuroinflammation, various 

faults in the neurotransmitter system, and other 

dysfunctional pathways and processes [20]. Also, PDD has 

a varied pathophysiology, according to certain research. 

Complex pathological alterations, such as the widespread 

deposition of α-syn, pathological changes similar to AD, 

and subcortical microangiopathy, are seen in patients with 

PD and cognitive impairment. Deposition of β-amyloid and 

tangles in nerve fibres are the primary pathological 

hallmarks of Alzheimer's disease [6, 21–23].   

 

3. Characteristics of Eye Movement in 

Patients with PD and Cognitive Impairment 
There are five main categories of eye-tracking tasks: 

saccade, gaze, smooth tracking, visual search, and social 

cognition. The two most common forms are fixation and 

saccade. When participants keep their gaze focused on one 

spot in space, it's called gazing; when they quickly move 

between two spots, it's called saccade. The two main types 

of saccades are autonomous saccades and reflected 

saccades. Easy focus and execution are required for reflex 

saccades, which are also called pro- or vision-guided 

saccades, to position the needle to a new object in the field 

of vision. The intentional tasks that arise from autonomous 

scanning in different models, on the other hand, may be 

classified as memory-guided, predictive, antiscanning, or 

deliberate scanning. The latter three types often need a 

greater degree of cognitive engagement and executive 

control. Saccades are the most common kind of eye 

movement abnormality in people with PDD.  

 

3.1. Reflective Saccade, also known as Overlapping 

Saccade). There is no need to give participants complicated 

or even distinct instructions when administering the reflex 

scan task; instead, they are just instructed to stare at the 

target fast and precisely, and the cognitive process may be 

recognised using simple overlapping procedures (Figure 

1(a)). Research on reflex saccade in people with 

Parkinson's disease and cognitive impairment, however, 

has shown conflicting findings [24]. Based on the findings 



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(a) (b) (c) 

FIGuRE 1: (a) Reflexive vision-guided scanning diagram: [1] the subject looks at the target point in the middle of the screen (yellow); [2] the 

target point appears randomly around the screen (green); and [3] the subject quickly looks at the random target point. (b) Smooth tracking 
diagram: the subjects looked at the target point and followed it to move at the same speed in the same direction until the target point disappeared. 

(c) Antisaccade diagram: [1] the subject looks at the target point that appears in the center of the screen (yellow); [2] the central target point 

disappears and a random target point appears around the screen (green); and [3] the subject looks in the direction opposite to the target point 

(white box). 

 
MacAskill et al. [26] discovered that the reduction in vision-

guided saccade is associated with the degree of cognitive 

decline, whereas suggestions [25] indicate that the latency 
and speed of eye movement in reflex saccade are 

comparatively conserved. Memory loss was also predicted by 

smaller reflex saccade amplitude, slower average speed, and 
shorter baseline latency in PD patients, according to a 54-

month prospective study by Stuart et al. [27]. This study 
showed that early PD patients had impaired reflex saccade 

function, amplitude, and speed when compared to age-

matched controls. Another research by Yu et al. [28] 
confirmed the impaired reflexive saccadic performance in 

Parkinson's disease patients, which worsened with 

deteriorating cognitive function. Patients with PD may be 
able to use reflex saccade as an indication of cognitive 

decline because to the negative link between prolonged 
latency and the Mini-Mental State Examination (MMSE) 

score.. Because AD solely affects complex saccade function, 

whereas PDD affects both reflex and complex saccade 
functions, Mosimann et al. [10] also suggested that 

impairment of reflex saccade might help distinguish between 

the two. 
 

Tracking with No Delay 3.1. Figure 1(b) shows that human 
eyes use smooth pursuit eye movement (SPEM) to follow a 

tiny, slowly moving object. The basal ganglia may have a role 

in the aberrant SPEM seen in PD patients [29, 30]. The 
inability or difficulty to initiate slow, deliberate movement is 

a hallmark of Parkinson's disease. When compared to healthy 

controls, patients with PD showed more saccadic eye 

movements during pursuit [31]. The control group that was 
considered to be in the normal range showed an early  

 

the component of smooth tracking in the direction that was 
proposed, a saccade to remedy the issue, and then an improved 

smooth tracking response. Contrarily, most PD patients 
employed saccade to track accurately, initial tracking was 

seldom generated before to scanning, and there was no 

evidence of improved smooth tracking after scanning. In 
addition, compared to the control group (low gain), patients 

with PD had a much decreased peak eye velocity throughout 

the follow-up period after scanning. Additionally, compared 
to those with normal working memory, PD patients with 

frontal brain dys-function had much greater mistake rates 
throughout smooth follow-up. According to single-photon 

emission computed tomography (SPECT), these patients 

exhibited low perfusion in the frontal lobe or frontotemporal 
cortex. This suggests that individuals with PD who experience 

working memory impairment may have dys-function in the 

frontal cortex [33, 34], leading to higher rates of predictive 
error during smooth tracking. An increase in irrelevant 

saccades or distractions, which mirrors the executive failure 
seen in PD patients, may be associated with SPEM 

abnormalities, according to other research [35].  

 
Section 3.2 treats antisaccade. When individuals engage in 



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SC 

GPi/SNr 

antisaccade, they concentrate their gaze on the visual signal 
located in the middle of the detection screen. After a 

predetermined period, the visual stimulus signal in the centre 
of the screen will appear in a random direction. The 

participants in this research had to look in the opposite 

direction of the visual stimulus signal that was in the middle 
of the screen; the signal occurred randomly in one particular 

direction (Figure 1(c)). Antisaccades are only effective when 

the subject is able to spontaneously scan in the opposite 
direction from the stimulus, rather than relying on their 

reflexive, visually directed scan [36]. According to some 
research, spontaneous  

 

There is no discernible decline in performance in later stages 
of PD, although early-stage symptoms such as saccade 

disorder and reduced saccade amplitude have been reported 

[37], particularly in memory-mediated saccade activity. 
Deterioration in saccade accuracy and extension of saccade 

latency are the most prominent symptoms of reverse saccade 
involvement, which worsens with the course of PD [26]. 

Waldthaler et al. [38] performed a meta-analysis and 

discovered that PD patients had a much higher mistake rate 
and reverse saccade delay, and that a longer latency of 

saccades was associated with higher exercise load and longer 
disease duration. In addition, Silvia et al. [36] demonstrated 

that the primary cause of the increased antiscan error rate in 

PD patients is not the inability to voluntarily scan in the 
opposite direction of the target, but rather the inability to 

control the reflex scan of unexpected targets. Further findings 

included the following: a higher Hoehn and Yahr (H & Y) 
score was positively linked with a greater reverse scan error 

rate, and the H & Y score, as an overall clinical stage 
evaluation tool, represented the degree of cognitive 

deterioration caused by the illness. While dopaminergic 

medication may have some correlation with PD progression, 
it has no discernible impact on reflex delay.  

4. Possible Mechanism of Eye Movement 

Disorder in PDD 

The decreased saccade amplitude observed in the PD patient 

may be due to basal ganglia dysfunction, which causes ex- 

 

 

FIGuRE 2: Anatomical pathways related to reflexive and 

voluntary saccades in Parkinson’s disease. A: dorsolateral 
prefrontal cortex; B: basal ganglia; C: superior colliculus; D: 
brainstem saccade gener- ator; E: visual cortex; F: parietal 

frontal lobe visual field; G: frontal lobe visual field. A ⟶ B 

⟶ C: autonomous saccade pathway; A ⟶ C: reflex saccade 
pathway. 

 

Cortex 
 

 

 

D1 Striatum D2 

cessive superior colliculus inhibition when the fronto-ocular 

signal gets transmitted from the substantia nigra reticular part to 
the basal ganglia. Autonomous saccade works through the 

cortical-basal ganglia-superior colliculus pathway, whereas 
reflex saccade starts directly from the cortex to the superior 

colliculus without passing through the basal ganglia, both of 

which are then projected to the brainstem saccade generator 
(Figure 2). The DA neurons in the pars compacta of the 

substantia nigra regulate the direct inhibition and indirect 
excitation of the striatum to the inner globus pallidus/substantia 

nigra reticular part by stimulating D1 and D2 receptors, 

respectively [39]. The loss of DA neurons in the substantia nigra 
pars compacta in PD leads to excessive activation of the inner  

 

 
 

 
 

globus pallidus/substantia nigra reticular part in the striatum, 

followed by over- inhibition of the thalamus (striatum-thalamus-
cortical cir- cuit) and superior colliculus, resulting in motor delay 

and random scanning disorder (Figure 3). Abnormal deposition 
of α-syn in DA neurons in the substantia nigra pars com- pacta is 

a pathological feature of cognitive impairment in PD. When the 

clinical signs of PD are prominent, DA 



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neurons in the substantia nigra compacta are seriously damaged, 
which may lead to excessive inhibition of the superior 

colliculus, prolongation of latency, and decrease in velocity and 
amplitude; this may also reduce the inhibitory effect on the 

superior colliculus, thus stimulating nerve impulses to produce 

unnecessary saccade [40] Subsequently, pathological deposits 

may continue to spread from the 

FIGuRE 3: Effect of dopaminergic neurons on saccade. SNc: sub- 
stantia nigra pars compacta; GPi: internal globus pallidus; SNr: 
substantia nigra pars reticulata; SC: superior colliculus. 

 

midbrain to the thalamus and cortex as the superior colli- culus 

circuit is gradually damaged, impairing cognition and 
aggravating eye movement dysfunction, which may explain 

the link between eye movement dysfunction, cognitive de- 

cline, and disease progression in PD [27, 41]. Studies have 

also shown [42] that the lateral prefrontal cortex is a vital 

area for saccade control, playing a central role in executive 

function, while lesions in this area are associated with many 

executive defects. In addition, the ability to inhibit incorrect, 

visually evoked eye beats depends, to a certain extent, on the 

integrity of the lateral prefrontal cortex, which further 

suggests that eye movement disorders are associated with 

impaired executive function. Executive dysfunction is the 

most prominent manifestation of the cognitive impair- ment 

observed in PD. Amador et al.’s research also showed [36] 

that executive dysfunction in PD was asso- ciated with a 

higher antiscan error rate, increased in- hibition times in 

delayed reverse scan tasks, and prolonged scan response 

times. 

 

5. Eye Movement Differences between PDD and 

Other Cognitive Disorders 
section 5.1. AD. Progressive memory loss, attention 

impairment, and executive dysfunction are hallmarks of 

Alzheimer's disease (AD), the most prevalent 

neurodegenerative dementia [43]. Acquired oculomotor 

impairments in Alzheimer's disease include saccade, 

fixation, and smooth pursuit. Saccadic tests revealed that AD 

patients had fewer precise saccadic movements and more big 

invasive saccades [44]. Eye movements in young-onset AD 

were compared with those of healthy controls of the same age 

by Pavisic et al. [43]. Compared to healthy controls of the 

same age, patients exhibited aberrant patterns of eye 

movement in the saccade, smooth pursuit, and fixation 

stability tests. In addition, the findings imply that high-order 

visuospatial and visuoperceptual integrations may be 

predicted using eye-tracking paradigms that are both simple 

and particular, which represent fundamental oculomotor 

properties. Patients with AD made more mistakes and spent 

less time following the goal during smooth pursuit tasks. In 

contrast to healthy older individuals, patients with AD 

exhibited increased antisaccade cost, latency variability 

across tasks, and latency overall (Noiret et al., 2015). It took 

longer for AD patients to fix erroneous antisaccades and 

there were more uncorrected antisaccades overall. When 

asked to forecast when a saccade will occur, older persons 

with AD had more gain and gain variability compared to 

healthy older individuals. The majority of saccadic eye 

movement characteristics shown strong correlations with 

dementia screening tests, particularly the MMSE and episodic 

memory measures, as well as with prosaccade, anti-saccadic, 

and predictive saccade tasks. This provides further evidence 

that executive and selective attention impairments may 

underlie saccadic eye movement abnormalities in Alzheimer's 

disease.  

 

Section 5.2 will cover DLB. Mosimann et al. [46] conducted 

experiments that tested PDD and DLB patients' reflexive 

saccade abilities, as measured by gap and overlap tasks, as 

well as their complex saccade abilities, including prediction, 

decision, and antisaccades. Saccadic eye movement 

alterations were seen in both DLB and PDD patients, with a 

protracted delay of horizontal saccades of all kinds, as well as 

defective predictive saccades and inhibition of saccades. Like 

patients with PDD, those with DLB have an increased delay 

of reflexive and voluntary saccades, the degree of which is 

correlated with the severity of the condition, according to a 

research [47]. Vulvovaginal palsy is a symptom that may be 

seen in some DLB patients. Horizontal and vertical saccades 

were less rapid and accurate, and the patients' variability was 

higher. Supravertical gaze paralysis is seen in a small number 

of DLB patients. People with DLB had trouble with basic 

saccadic eye movement tasks as well as more advanced ones, 

and they also had trouble with reflexive and saccadic 

execution. Furthermore, studies have shown that akinesia and 

stiffness often accompany convergence issues [48].  
 

6. Feasibility and Advantages of Using an Eye 
Movement Instrument to Evaluate Cognitive 

Impairment in PD 
As of right now, there isn't a solid biomarker that can detect 

neurodegeneration or monitor the development of 

cognitive impairment in PD. Neuropsychological screening 

measures are now the gold standard for clinical diagnosis 

of PDD. Screening techniques with greater accuracy need 

substantial time and resources, including experienced 

medical personnel and significant training, yet they are 

adequate in diagnosing AD and moderate cognitive 

impairment (MCI). In addition, the degree of education of 

the receiver and the expertise of the assessor have a 

significant impact on the outcomes [49–52]. On the other 



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hand, eye tracking may provide quantitative parameters 

and millisecond-level precision [53]. To objectively 

quantify cognitive impairment in PD patients, we used a 

particular eye-scanning technique to investigate the 

cognitive process behind visual abnormalities. With the 

use of eye movement tracking technology, it is possible to 

record the dynamic features of behaviour in the natural 

world in a way that is more objective, trustworthy, and 

scalable. This paves the way for the processing and 

quantitative analysis of objective data [54]. Patients with 

cognitive impairment may have their illness development 

monitored nonverbally and with less cognitive load using 

eye movement monitoring [55]. Recording eye 

movements does not need any extra behavioural reactions, 

unlike many conventional neuro-psychological 

evaluations. Eye movement tracking is ideal for patient 

research since it is noninvasive and does not have any 

contraindications [43]. Evidence is mounting that standard 

cognitive evaluation instruments and data gathered from 

eye movement monitoring have a strong association. Eye 

movement monitoring seems to be a viable tool for 

assessing and tracking the cognitive state, severity, and 

development of neurological disorders [36].  

Screening for cognitive problems in neurological illnesses 

has piqued the interest of eye-tracking technologies in 

recent decades. Using an electro-phthalmography 

equipment, Thickbroom and Black [56] were the first to 

discover aberrant eye movement in multiple sclerosis. 

They measured eye movement during  

monitoring responsibilities. Eye movement abnormalities 

may include either the extrapyramidal or supratentorial 

cones, as was shown in another research [57] that included 

ALS patients. Based on these results, watching eye 

movements might be a useful diagnostic technique for 

gauging illness course and prognosis. Eye movement 

tracking may have use in the differential diagnosis of 

Parkinson's syndrome[58,59] since several age-related 

degenerative disorders are associated with aberrant 

patterns of eye movement. These patterns vary among PD, 

cortical-basal syndrome, PSP, and MSA. A growing body 

of research suggests that indicators that monitor eye 

movement may do more than just digitally record the eye's 

spatiotemporal trajectory and movement characteristics; 

they can also reflect sophisticated cognitive information 

and even forecast the onset of particular cognitive 

impairment. These markers differ because of variations in 

disease features, individual variances in perception, and 

the severity of cognitive impairment [55]. During gaze 

and smooth tracking tasks, several brain regions were 

discovered to be active, including the thalamus, anterior 

cingulate cortex, auxiliary motor area, superior colliculus, 

and frontal insular cortex [60, 61]. Tasks requiring 

executive function, such as scanning, smooth tracking, 

visual search, and social cognitive processing, engage a 

network of cortical and subcortical regions [62]. Thus, the 

eye movement tracking index offers a wealth of 

information for investigating the brain's inner workings, the 

connections between behaviour and cognition, neural 

processes, and brain function [63, 64]. Saccade activity 

impairment may be an early indicator of cognitive 

impairment in PD, as shown by Walton et al. [65] in their 

study of patients with PDD compared to those with PD 

without cognitive impairment. Patients with PDD were 

more impaired with regard to complicated saccade and 

reverse saccade movements. Prolonged saccade delay was 

shown to be more than 60% sensitive and 88% specific in 

differentiating PD from PDD, according to Mosimann [66] 

and other research. Even at an early stage, the amplitude of 

the reflex saccade in PD patients reduced somewhat, 

according to a case-control research [26] conducted by 

Macaskill et al. In addition, later stages of the illness are 

generally associated with greater saccade delay in older 

individuals with increased motor and cognitive 

impairment. If a patient has full cognitive function, their 

scan latency should be about the same; if they have 

cognitive impairment, it would progressively be longer. 

The varying amplitudes and latency of spontaneous 

saccades, together with their gradual deterioration, suggest 

that they might be a valuable objective tool for evaluating 

the illness status. According to these results, the reflex 

saccade parameters for motor and cognitive symptoms in 

PD might be reliable indicators of these conditions, and 

they could be used as biomarkers to monitor the 

development of the illness and the efficacy of 

neuroprotection and neurorecovery treatments. When it 

comes to motor illnesses like Parkinson's, eye-tracking 

studies are ideal for assessing cognitive function because  

They are less impacted by motor retardation in PD since 

they do not rely on motor responses and simply need basic 

eye motions.  

 

7. Summary and Prospect 
There are currently few options for detecting cognitive 
impairment in early Parkinson's disease. Research methods 

and tools for the detection of cognitive dysfunction are 

currently limited, and there are still challenges to conducting 
objective and large-scale screenings of cognitive impairment 

in the community. This is mainly due to the high cost, stringent 
testing requirements, and invasive nature of cerebrospinal 

fluid, peripheral blood, or neuroimaging [67]. Saccade 

monitoring has the potential to be a dependable and user-
friendly biomarker, as several research on neurodegenerative 

diseases have shown that saccade controls have degraded to 
different degrees. There is a lot of activity in the area of 

cognitive testing that uses eye movement. Saccade has gained 

popularity as a method for assessing cognitive abilities and eye 
movement control because to its readily measurable dynamic 



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features and well-defined anatomical circuits. Research is 
being conducted with the objective of making the tools more 

accurate and reliable. Many studies on Alzheimer's disease 
have shown a strong relationship between EMG parameters 

and cognitive performance; however, there is a dearth of 

research on the topic of cognitive impairment and EMG in 
Parkinson's disease patients, and what little there is is mostly 

cross-sectional. Different methods used to identify people, 

instruments, and durations of follow-up in previous 
longitudinal research may explain why their findings vary. 

To validate the role of eye movement in Parkinson's disease 
development, more longitudinal follow-up studies are 

required. The elderly also often have trouble with memory-

guided scanning and reverse scanning. When it comes to 
scanning tasks, patients with mild cognitive function 

typically have no problem. However, when it comes to 

patients with severe cognitive impairment, eye movement is 
typically not an option because patients with severe cognitive 

impairment struggle to cooperate in order to implement the 
corresponding saccade paradigm. The acquired data can end 

up being inaccurate because of this. That is why it is essential 

to establish quantitative standards in order to have useful and 
effective assessment criteria. Furthermore, most studies 

found that individuals with PD used more dopaminergic 
drugs—drugs that might influence eye movement—during 

the test. To avoid this confounding impact, future research 

should compare PD patients taking medication with those 
who do not. Furthermore, there is a lack of consistency in the 

equipment used to detect eye movement and in the standards 

used to measure saccade indicators such as error rates, proper 
antisaccade delay, and error latency in the available research. 

The outcomes of the study might be skewed due to bias or 
mistake. In order to make the results more credible and 

consistent, it could be helpful to fix the possible problems 

with the spatial/temporal resolution, noise, calibration, etc., 
of existing eye-tracking hardware and software. Eye 

movement tracking in conjunction with other biomarkers and 

clinical tools has the potential to provide the  
most effective method for predicting cognitive deterioration 

and, eventually, for early, more tailored therapy of PDD.  
 

Ethical Approval 

The manuscript does not contain clinical studies or patient 

data. 

 

Conflicts of Interest 

The authors declare that they have no conflicts of interest. 
 

Authors’ Contributions 

All authors had full access to all the content in the study and 

are responsible for the completeness and accuracy of the 

content. Xianglian Liao and Jian Yao are mainly responsible 

for manuscript drafting and manuscript editing. Hongyin 

Tang, Yilan Xing, Xin Zhao, and Daao Nie contributed to the 

literature search, and Guihua Li and Ping Luan were re- 

sponsible for reviewing and guiding the manuscript. All the 

authors have read and approved the final manuscript. 

Xianglian Liao and Jian Yao contributed equally to this 

work. 

 

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