Saccades play an essential part in the assessment of movement disorder patients. It is particularly helpful to evaluate both horizontal and vertical saccades independently as different disorders impact them differently.
This exercise is an effective and straightforward way to objectively measure saccadic performance. It’s straightforward and straightforward for administrators and scorers alike.
Vertical Saccades
Saccades are eye movements that quickly shift the eyes from one point to the next. They are essential for clear vision, reading, and focusing and are required for smooth visual acuity in various environments. Saccades may also be initiated by external stimuli like sounds or objects outside your field of vision; moreover they may even come directly from the brain via signals presented at frontal eye fields (FEFs).
The FEF receives input from the anterior cingulate cortex and sends corticofugal projections that end at the superior colliculus of the midbrain, where they control involuntarily generated saccades. When initiating voluntary saccades, however, FEF initiates movement while superior colliculus regulates velocity and timing; both areas also receive inputs from other cortical areas responsible for stimulus processing, motor control and saccadic integration.
When undertaking oculomotor training, it is critical to measure and compare metrics such as latency, amplitude, peak velocity and acceleration of saccades to see if movement has improved. A reliable way of doing this is with an eye-tracked oculomotor testing device.
Developmental Eye Movement (DEM) testing is an efficient and straightforward method to assess saccades. This test can be administered and scored quickly and is intended for 5-13 year-olds but its results remain valid even among adults.
The DEM test involves two strips of vertical letters which patients read from left to right and top to bottom in a timed test, providing objective data regarding saccade accuracy. Results from this timed test provide objective measurements which can guide treatment decisions as well as provide a basis for improvement.
Research has demonstrated that those suffering from mild TBI exhibit abnormal vertical saccades, with larger position errors, smaller amplitudes and slower peak velocities and accelerations than controls. These saccades may be affected by both cognitive and affective components of their NSI; poor saccades may contribute to fatigue, slow information processing, reaction times that are slower than expected, poor multitasking ability or “brain fog”, poor visual clarity as well as emotional lability symptoms.
Horizontal Saccades
Saccadic eye movements involve shifting one object’s gaze from another object quickly and often moving your eyes from left to right or vice versa, similar to reading or driving a car. They play an essential part of reading, driving and other complex visual tasks requiring rapid eye movements; their disruption may cause symptoms like poor reading performance, multitasking issues and confusion or brain fog.
Saccades are controlled primarily by the frontal lobe and pontine paramedian reticular formation in the brainstem, sending burst-velocity signals from these circuits to motor neurons in the cerebellum to generate saccade amplitude and direction, with final eye position checking through vestibular system feedback loops. Damage to any of these structures results in either inability to control saccades or mismatch between planned and actual saccade trajectories.
Abnormal saccades may occur as the result of various brain conditions, ranging from mild traumatic brain injury (mTBI) to stroke and Parkinson’s disease. Depending on the underlying pathology, different control circuits in the brain may be affected, leading to different saccade paths; lesions in the dorsolateral prefrontal cortex could for instance result in abnormally slow self-paced saccades with reduced antisaccade speeds as a result of controlling timing, amplitude and velocity as well as accuracy regulation by this area alone.
Parkinson’s disease patients tend to exhibit slower vertical than horizontal saccades, often accompanied by an ocular tremor. This could be caused by impaired sensory input from their eyes, delayed transmission of saccade control signal transmission and reduced saccadic adaptation. Patients may also display square wave jerks or macrosaccadic oscillations which involve small saccades away from and back towards midline with an intersaccadic interval between each saccade.
Ocular saccade abnormalities include slower downward and reduced upward movement known as slow-downs or downbeat nystagmus, seen frequently among patients suffering from multiple system atrophy (MSA), particularly the cerebellar form (or MSA-C or olivopontocerebellar ataxia). Damage to an oculomotor nerve may cause vertical supranuclear palsy while lesions to the superior colliculus may produce gaze-evoked nystagmus.
Side to Side Saccades
Saccades are rapid eye movements that quickly move the eyes from one fixation point to another, and are essential for many visual tasks such as reading, driving and following moving objects such as balls. Unfortunately, vision loss, glaucoma or trauma may interfere with saccades.
Saccades may be instinctive movements, but with practice they can be modified consciously to become more accurate and reduce wasteful saccades. This practice is known as saccade adaptation. It involves assessing past saccades’ accuracy before correcting motor commands for future saccades in order to enhance accuracy – this process usually occurs unconsciously as individuals complete trials over time.
Visual therapy exercises that can help assess and train saccades include Hart Chart Saccades, Saccade Sticks and Optokinetic Nystagmus Fast Phase (OKN FPP). These can be completed both seated or standing; quickly moving eye focus from side to side using visual cues such as wiggling fingers or moving lights can be challenging for muscles systems to accurately complete these fine movements.
Frontal eye fields, supplementary eye fields and superior colliculus all play an essential role in controlling voluntary saccades. These structures connect directly with brainstem saccadic generators but may also be affected by frontal cortex and Brodman’s area 8.
Saccadic intrusions or oscillations occur when eyes display abnormal movements during smooth pursuit or saccade execution, such as square wave jerks, macrosaccadic oscillations or even ocular flutter/opsoclonus.
One common cause of saccade inaccuracy is an undershoot in the direction of its intended target, often as the result of mismatched durations for its phasic and tonic innervations, leading to it stopping short of the target before returning back towards its starting point.
Saccades are complex yet essential visual movements that must function efficiently to function as intended, but when they don’t, their ineffectiveness can have devastating repercussions for reading ability and eye strain/fatigue, words “swimming” around on pages, headaches and misdiagnosis of dyslexia. Therefore it is vital that children undergo evaluation of the quality of their saccadic movements.
Vertical Loops
Saccades may resemble rollercoaster rides for your eyes; in reality they’re ballistic movements executed multiple times every second by various eye muscles such as the lateral, medial, and superior rectus muscles to quickly shift fixation from object to object.
These muscles, located in the frontal cortex of the brain, have direct access to saccade-generating circuitry. Not only can these muscle fibers generate necessary eye movements but they can also be used to regulate its amplitude and duration.
An example is a saccade, where its amplitude refers to how far an eye travels during its movement; degrees or minutes of arc are used as measurements of this distance traveled, while duration refers to how fast this process took place (usually reported as seconds of arc).
Eye tracker measurements of saccades allow researchers to compare them against an ideal saccade profile with zero degrees of arc velocity as the target velocity. If eyes fail to achieve this ideal, it is considered saccade error which must be rectified by repeating it again.
Carrying out vertical loops improves gaze stability, helping you see more detail and focus more intently on objects and events around you. Furthermore, this exercise builds muscle strength within your eye area that reduces ocular fatigue.
To conduct this exercise, place two vertical targets approximately one foot apart on either side of your body and use both eyes quickly bouncing up and down between them, stabilizing your head before doing this exercise with either one eye covering the other to increase accuracy, or both eyes simultaneously. Pace yourself using a metronome or make this harder by increasing target separation further apart or performing it in a busy location like tracking people around you – this can help enhance awareness of your surroundings in crowds.
