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?
There are various effects which persist after acute medical treatment such as sensory, motor, perceptual, physical, behavioral, cognitive, linguistic and emotional. Some common symptoms can be headache, fatigue, sleep disturbance, irritability, dizziness, subjective cognitive impairments, sensitivity to light and noise, nausea and depersonalization.
For vision the following areas can be affected:
- 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: convergence (crossing the eyes together to aim at a near object) and divergence (relaxing the eyes to aim at a more distant object). If eye teaming skill is affected, this could result in double vision or reduced depth perception which would affect the ability to play sports, mobility and orientation in space, watching 3D movies, etc… From most common to least common eye-teaming disorders due to TBIs are convergence insufficiency (the eyes can’t turn in enough) , binocular instability (eyes turn in or out at varying amounts randomly), convergence excess (eye turning in too much) and divergence insufficiency (the eyes don’t turn out enough at distance).
- Eye Tracking: fixation (locking on to an object and follow it) and saccades (changing fixation from one object to another). This is important during reading since we need to track words across sentences and then re-fixate from end of one sentence to the next. Patients with TBIs can 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.
- Eye Focusing: Accommodative facility (the ease of switching eye focusing between different distances) and accommodative amplitude (the maximum amount of focusing the eyes can do). Damaged eye focusing skill can result in blurry vision.
- Visual Perceptual Processing: Visual attention span (able to concentrate on the relevant visual information while ignoring other parts), visual processing speed (taking in and understanding visual information), visuospatial memory (recognizing your own environment and the spatial orientation of objects in there), and visual memory (remembering what you have seen before)
What are the possible treatments?
The advocated treatment is multidisciplinary approach: general physicians, optometrists, occupational therapists, physiotherapists, psychologists, speech pathologists, and other specialists depending on associated symptoms.
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, head injuries, mood and anxiety disorder, being a student, sustaining the injury in a motor vehicle accident and age over 40 years old.
How long should you expect before seeing improvement?
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.
Why 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 referred 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 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 paragraphs…
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