What is traumatic brain injury?
Traumatic brain injury (TBI) is defined as any damage or alteration to brain function due to external physical force. TBIs can be caused by falls, motor vehicle accidents, assaults, concussions, gun shots, or explosions and blasts etc. There are three levels of TBI: mild, moderate and severe. About 80-90% of TBIs fall in the mild category, which is most responsive to vision therapy and rehabilitation.
What are the side effects?
Over 50% of brain pathways relate to visual function, which explains why many patients with TBI may experience one or more of the following vision problems.
- Light and Visual Sensitivity: Many brain injured patients develop a hypersensitive and fragile visual system. Slight changes in prescription and visual environment such as lighting (fluorescent and computer screens) and patterns can very noticeable. Also, the visual system’s ability to filter out visual noise is impaired, making motion and crowded spaces overwhelming. In addition, one’s ability to organize oneself in visual space is impaired, resulting in overwhelming sense of discomfort, vertigo and/or imbalance.
- Visual Hallucination: Visual hallucinations may occur as stars, flashes and spots. The formed images may represent misunderstanding of information in the brain or background “noise” from the disruption of brain tissue that is needed to process the information.
- Eye Teaming: This describes how the eyes coordinate to convergence (crossing the eyes together to aim at a near object) and divergence (relaxing the eyes to aim at a more distant object). An unstable and weak eye-teaming system may result in double vision or reduced depth perception which would affect mobility and orientation in space and watching 3D movies.
- Eye Tracking: The eye’s ability to fixate (locking on to an object and follow it) and make saccades (changing fixation from one object to another) is important for many activities of daily living. For example, when reading, we need to track words across sentences and then re-fixate from end of one sentence to the next. Patients with TBIs may also experience nystagmus, an ocular condition where the eye(s) drift off the target and then correct it to re-fixate resulting in continuous movement of the eye during fixation. This would reduce visual clarity and affect balance.
- Eye Focusing: Our eyes’ ability to sustain and switch focus between near and far objects are often damaged in patients with TBI. This can result in intermittent blurry vision, eye strain, headaches around the forehead, fatigue and inability to perform near work for a sustained period of time.
- Visual Perceptual Processing: Patients with TBI often report cognitive “fog” resulting in reduced visual attention span (ability to concentrate on the relevant visual information while ignoring other parts), visual processing speed (taking in and understanding visual information), visuo-spatial memory (recognizing your own environment and the spatial orientation of objects in there), and visual memory (remembering what you have seen before).
- Hemianopsia: This is when a patient suffers from a visual field loss where half of one’s visual field, either vertically or horizontally, is gone; the person cannot see it. Saccadic eye movement training (scanning vision therapy) can help restore some vision in patients with neurological vision loss.
What are the possible treatments?
The advocated treatment is a multidisciplinary approach: optometrists, physicians, physiotherapists, occupational therapists, psychologists, speech pathologists, chiropractors and other specialists depending on associated symptoms. Click here for more information on neuro-optometric approach to TBI management.
What is the prognosis?
The prognosis for recovery worsens if symptoms persist past the three months mark, and certain personal factors such as persistent physical illness, prior neurological diseases, multiple head injuries, mood and anxiety disorder, sustaining the injury in a motor vehicle accident and age over 40 years old.
How does the training work?
After a traumatic brain injury, certain parts of the brain are turned off due to damage, or cannot communicate with other parts due to severed connections. Neuroplasticity refers to the brain’s ability to rewire itself and make new connections throughout life. By introducing different repeating stimuli, we are essentially retraining the brain to use remaining areas to compensate for the damaged parts, or rewiring the neural connections allowing for better communication within the brain. The stimuli can be creating different blurs by using different lenses in front of the eyes, or introducing eye tracking exercises such as following a ball or searching for specific letters within a paragraph.
How long should you expect before seeing improvement?
In one study, following the training of 6 weeks with half an hour per week, the accommodative facility for each eye and both eyes together increased from 5 cycles per minute to 11 cycle per minutes (age-matched normal is 11 cycles per minute for each eye, and 8 cycles per minute for both eyes together). The accommodative amplitude in each eye increased from 6D to 8D after vision therapy (age-matched normal is 9-10D).
Similarly, with 6 weeks of training and half an hour per week, the eye teaming skills have increased in the majority of subjects (about 80%) compared to receiving no visual therapy. Visual attention span increased from 32nd percentile to 50th percentile for 80% of the subjects included in the study.
Eye tracking skills have also showed improvement during a study comparing between undergoing 8 weeks of vision therapy with two sessions per week for 45 minutes/session. The horizontal fixation error rate has decreased while the ability jump from one object to the next has increased.
Study done on adults suffered mild, moderate and severe TBIs undergoing 40 hours of computerized cognitive training over 10-12 weeks have showed improvement in visual processing speed, non-verbal reasoning correct responses and reaction time.
From all the studies reviewed, it showed that at least 6-10 weeks of visual therapy is expected before any improvements can be observed.
References
Neuro-ophthalmologist at the Wilmer Eye Institute of Johns Hopkins University, Dr. Eric Singman, writes on Vision Rehab and Brain Injury.
Dr Singman authored a three part article on Vision and Rehabilitation after Brain Trauma that you can access online via brainline.org
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