Smooth pursuit eye movements are an essential aspect of vision and our ability to track moving objects traveling less than 30 degrees/sec. When we look at a moving object, such as a passing car, a bird flying by, or even a bouncing ball, our eyes instinctively engage in smooth pursuit eye tracking to maintain a clear and continuous fixation on the object of interest.
Smooth pursuit eye movements not only enable us to visually track objects but also contribute to our overall perception of motion, depth, and spatial relationships. They play a vital role in activities such as sports, driving, and even reading, where the ability to smoothly track a moving target is crucial for accurate and efficient visual processing.
The underlying physiological process of smooth pursuit eye tracking involves a complex interplay between various neural pathways from the brain and eye muscles that work together to help maintain focus on a moving target and stabilize the object on the fovea. The fovea is a part of the retina responsible for vision and processing incoming visual information.
Specialized cells, located in specific regions of the cerebral cortex and brainstem, coordinate the precise movement of our eyes in response to the velocity and trajectory of the moving target. Smooth pursuit eye tracking can occur in any direction of gaze including horizontal, circular, and vertical.
A concussion is a type of traumatic brain injury that can disrupt normal brain function. The visual system is largely interconnected with most areas of the brain (roughly 60%). As such, following a concussion, specific visual areas of the brain, as well as integrative pathways, can be affected, resulting in visual dysfunction.
The prevalence of vision problems following a traumatic brain injury, like a concussion, is roughly 50%. Concussion related vision problems can involve impairments to eye movements, eye reflexes, eye tracking, focusing, visual acuity and pupil function. Unless an individual is assessed properly following an acute concussion, these visual problems generally get missed, since most individuals are not aware that their symptoms may be coming from their eyes and visual integration system. Occasionally, patients report visual symptoms that are specific to the eyes (blurred vision, light sensitivity, eye fatigue, double vision, impaired peripheral vision etc.), however, often the concussion symptoms are vague, such as headaches and dizziness. See below for common visual symptoms following a concussion.
Research has shown that traumatic brain injuries can affect smooth pursuit eye tracking. This is due to the damage that occurs in the pathways of the brain responsible for controlling these movements. As a result, concussion patients often struggle with tracking even slowly-moving objects accurately. In addition to difficulty with these types of activities, patients complain of dizziness, headaches or nausea while attempting to perform them. Smooth pursuit eye tracking can be affected in several ways following a concussion:
Head trauma can disrupt the ability to smoothly track moving objects. The precision and accuracy of smooth pursuit eye movements may be compromised, leading to difficulties in smoothly following a moving target.
Concussion patients may experience a diminished range of smooth pursuit eye movements. They may struggle to track objects that move at different speeds or across larger visual fields.
Following a brain injury, there may be a delay or latency of smooth pursuit eye movements. This delay can make it challenging to keep up with rapidly moving objects or to anticipate their trajectory accurately.
It is not uncommon for traumatic brain injuries to result in asymmetrical eye movement, where one eye may lag or deviate more than the other during eye tracking.
These various alterations in smooth pursuit eye tracking can disrupt visual processing and affect daily activities following a head injury. It can lead to difficulties in maintaining focus, tracking objects in motion, and judging distances accurately.
Smooth pursuit eye tracking serves as part of the diagnostic testing used to assess the patient’s ability to accurately track a visual target in a smooth, controlled manner. Smooth pursuit eye tracking tests should be assessed in both horizontal and vertical directions, because these different types of movements have different pathways. The following are directions outlined by the Vestibular Ocular Motor Screen (VOMS), which is an assessment tool that looks at the systems in charge of integrating balance, vision, and movement.
The smooth pursuit test should be assessed bilaterally and in both horizontal and vertical directions to provide a complete picture of the patient’s ocular motor control. It is quick and easy and should be part of a concussion assessment. The results of this test can help identify any abnormalities in the oculomotor system or vision deficits in the ability of the eyes to track moving targets, which may indicate damage from a suspected concussion.
To learn more about other vision tests to include in your assessment, read our previous blog article here: A Look at the Eyes: Assessing Vision In Concussion Patients
The King Devick test is another clinical tool commonly used to assess smooth pursuit eye tracking and other visual skills to evaluate concussions. The King Devick test consists of a series of increasingly difficult numbers that the person must read aloud as quickly as possible. The practitioner will then measure the time it takes for the patient to complete the task, and changes in the time taken can indicate abnormalities in smooth pursuit eye tracking.
Studies have found that there is a significant correlation between concussion and slower results on the King Devick test. A study by Pardini et al. (2012) demonstrated that individuals with a concussion took significantly longer to complete the King Devick test than those without, indicating impaired smooth pursuit eye tracking. Furthermore, the slower response times on the King Devick test have been found to be significantly associated with other vision symptoms of concussion such as headache, dizziness and concentration deficits.
It’s important to note that the effects of a brain injury on smooth pursuit eye tracking can vary from person to person, and the severity and duration of these effects can also differ. In some cases, these visual deficits may resolve on their own as the brain recovers from the concussion. However, symptoms can persist beyond the acute phase of a concussion and develop into what is known as post-concussion syndrome. Post-concussion syndrome refers to a condition where symptoms associated with a concussion persist for months after the initial injury.
When individuals experience persistent vision symptoms as part of post concussion syndrome, it is crucial to seek medical attention from healthcare professionals who specialize in concussion assessment and who have expertise in managing these symptoms. An appropriate specialist may include a neuro optometrist who has clinical practice experience in concussion assessment and treating persistent visual symptoms associated with a traumatic brain injury.
Vision rehabilitation or therapy is one way to improve smooth pursuit eye tracking and other aspects of visual functioning that may be affected in the aftermath of a traumatic brain injury. Vision therapy can help improve tracking accuracy, speed, and symmetry and reduce ongoing visual symptoms. Treatment may include exercises that target specific eye movements, visual processing activities, and special lenses or glasses as prescribed by a neuro optometrist. With appropriate rehabilitation and guidance from a trained professional, people affected by a concussion can improve their visual function and quality of life.
Following a head injury, the occurrence of visual symptoms is prevalent. In order to ensure accurate diagnosis and effective management of concussions, healthcare professionals must employ comprehensive assessment tools, including smooth pursuit eye tracking. This enables healthcare professionals to identify any irregularities or deficits in the ability to smoothly track objects. By pinpointing such impairments, they can accurately diagnose and manage the effects of the concussion, tailoring treatment plans to address the specific visual deficits present. Healthcare professionals trained with Complete Concussions, specialize in concussion diagnosis and management. If you have any questions contact us here.
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