V.Balaje, Bachelor in Optometry
Master in Optometry Student, Manipal College of Health Professions
Saccadic eye movements (SEM) are an innate and essential part of our lives, which is being executed every day – both voluntarily and involuntarily.(1, 2) These are basically rapid eye movements done to fixate the fovea on any object of interest.(3) Though all types of eye movements are controlled by various cortical pathways, SEM are a lot more intertwined to the cognitive function of an individual.(4) Relating to the cognitive function, SEM tasks include visually guided prosaccades (movement towards the stimuli) and antisaccades (movement towards the opposite direction of the stimuli).(3)
Figure 1: Prosaccade task: eye movement should be done towards the black circle. Antisaccade task: eye movement should be done towards the exact opposite direction to the stimuli (Image Courtesy: Tschan, D. G. (2017). Influence of Uncertainty and Fixation on Human Antisaccade Performance (Doctoral dissertation, Universität Zürich)
Multiple modalities of recording the characteristics of saccadic eye movements and its cortical involvement have been incorporated through the ages, which includes Eye trackers, Electrophysiological recordings and Magnetic resonance imaging (MRI).(5-7) Antisaccades, as stated by different literatures, have longer reaction time (RT) and delayed latency in eye tracking and electrophysiology recordings, due to increased cortical preparation, and activates a different location in the brain when compared to the prosaccades.(5, 7, 8)
Figure 2: (A) EEG electrodes placed and its recordings (B) MRI images of cortical activation (C) Eye tracker (Image courtesy:
(A) Siuly S., Li Y., Zhang Y. (2016) Electroencephalogram (EEG) and Its Background. In: EEG Signal Analysis and Classification. Health Information Science. Springer, Cham.
(B) Richards, J. E. (2013). Cortical sources of ERP in prosaccade and antisaccade eye movements using realistic source models. Frontiers in systems neuroscience, 7, 27.
Graph 1: Reaction time in Prosaccade and Antiasccade tasks of young adults, Older adults and PD group (Longer RT in PD group and older adult group in both Prosaccade and Antisaccade task)
(Graph courtesy: Ouerfelli-Ethier, J., Elsaeid, B., Desgroseilliers, J., Munoz, D. P., Blohm, G., & Khan, A. Z. (2018). Anti-saccades predict cognitive functions in older adults and patients with Parkinson’s disease. PloS one, 13(11), e0207589)
Measuring and analyzing the characteristics of SEM have been performed in various studies to assess the cognition in neurodegenerative diseases and older individuals. Patients with neurodegenerative diseases such as Parkinson’s disease (PD), Alzheimer’s disease (AD), Multiple sclerosis (MS), Glaucoma, etc. tested with prosaccade and antisaccade tasks show longer RT, difficulty in control and execution of the saccades (in antisaccade tasks), larger error rates, etc. than the normal population group (age matched controls and younger population). The cause of the difference in the SEM tasks are believed to be due to the impaired cognitive function (inhibitory control and task-switching ability).(9-12)
Also, examining older adults with the SEM tasks (prosaccade and antisaccade) resulted in longer RT and higher error rates than the young adults and it was due to the processing speed decline and alteration of the executive function, due to ageing, which are basically part of the cognitive function.(13)
These SEM tasks have also been implemented in assessing cognitive function in children with neurodevelopmental disorders such as Developmental co-ordination disorder (DCD), Autism, Attention-deficit/hyperactivity disorder (ADHD), etc.; and the main findings were poor inhibitory control and difficulty in remembering the target location to execute a saccade. These impaired attentional abilities will further lead to improper functional growth of motor skills as they age.(14-16)
An important note from all the above-mentioned literatures is that, the outcome measures of the SEM tasks were correlated with other clinically available cognitive function tests and neurophysiological tests and it stated that outcome measures of the SEM tasks (RT, amplitude, error rates, etc.) were good predictors of decreased scored in other cognitive tests and the vice-versa.
In conclusion, it is established that SEM tasks are of great help in assessment of cognitive function in various scenarios, but the use of these tasks, clinically, is not well developed. These simple SEM tasks have great capacity of being implemented in identifying the presence of neurodegenerative diseases than the use of difficult tests.
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- Ouerfelli-Ethier, J., Elsaeid, B., Desgroseilliers, J., et al (2018). Anti-saccades predict cognitive functions in older adults and patients with Parkinson’s disease. PloS one, 13(11), e0207589.
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- Ouerfelli-Ethier, J., Elsaeid, B., Desgroseilliers, J.,et al (2018). Anti-saccades predict cognitive functions in older adults and patients with Parkinson’s disease. PloS one, 13(11), e0207589.
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