By: Aurelia Wiltshire, OTR/L, CBIS
Rainbow Rehabilitation Centers
Most people think of the eyes and their ability to clearly “see” a target, such as a clock or a sign as a definition of vision. If your vision is poor, you would probably see an eye doctor and get corrective lenses or consider laser or cataract surgery.
Someone familiar with basic anatomy may tell you that the primary area of the brain for vision is the occipital lobe, and think of vision as a connection between the eyeballs to the occipital lobe via the optic nerve.
We now understand that vision is much more complex. Vision encompasses everything from the ability of a person to control their eye muscles to search for and find a target, fixate on it, maintain fixation on the target long enough for the internal structures of the eye to focus on it (with or without glasses or contacts), and interpret the target.
Many vision researchers define vision as the ability to process, organize, and interpret what is seen and then act on it. The neural pathways that involve vision, and understanding what is seen, divert into all lobes of the brain. It is not simply a direct connection from the eyeballs to the occipital lobe as once thought.
The visual system begins with the eye. Incoming light passes through the pupil to the retina. The retina has cells that pass through the optic nerve, the optic chiasm, wrap around the midbrain, cross the temporal lobe and terminate in the lateral geniculate nucleus (LGN), which is part of the thalamus. From there, the cells travel in pathways throughout the brain. The various lobes of the brain act together to interpret the image. Any deficit along the pathway may result in visual dysfunction.
Studies have found that persons with acquired brain injury (ABI) have a much higher incidence of certain vision deficits when compared to the expected prevalence in the general adult population. (Table 1)
Vision deficits have been so prevalent among service members diagnosed with TBI, that in 2007 the The U.S. Department of Veterans Administration (VA) modified its standard of care to include vision assessment for everyone with a TBI (Scheiman, 2013).
Visual deficits are not always recognized by medical personnel, patients or their families, or taken into consideration during rehabilitation after a brain injury. After brain injury, patients generally fail to articulate complaints due to impaired subjective experience and reduced cognition. The person with a TBI may be labeled as confused, clumsy, anxious, uncooperative, or unmotivated by professionals who are unaware that vision deficits may be the cause of the patient’s behavior.
When vision is addressed in the rehabilitative setting it is usually from a strictly medical perspective, with attention given only to visual acuity and eye health (Scheiman, 2011).
Visual deficits outside of this scope are often not recognized, understood, or addressed. However, this is beginning to change. There is ongoing research into the components of vision and how they interact and intertwine to produce “normal vision.”
What is Vision Therapy?
According to the American Optometric Association, vision therapy is a sequence of neurosensory and neuromuscular activities individually prescribed and monitored by the doctor to develop, rehabilitate and enhance visual skills and processing.
Dr. Mitchell Scheiman, a nationally known optometric educator, lecturer, author, and private practitioner, has proposed a three-component model of vision in order to organize a rehabilitation approach to vision. The components include an evaluation of:
- Visual integrity including visual acuity (the ability to focus and see clearly at various distances) and eye health.
- Visual efficiency including visual accommodation (the eye’s ability to shift focus so that objects at different distances can be seen clearly), binocular vision (the ability to properly combine images from each eye into one image) and eye movements.
- Visual information processing including visual spatial, visual analysis, and visual motor integration skills.
The following is an outline of the visual screening process that Dr. Scheiman designed:
Vision screening usually begins with a questionnaire to determine what, if any, symptoms are being experienced by the client.
A therapist screening for visual integrity dysfunction has several tools that can be used in the clinic. These include the Snellen Chart (appropriate for clients age 6 to adult) and the Lea Symbol Test (appropriate for clients age 2 . to 6 or for clients of any age who have sustained a brain injury or have difficulty with English letters).
These tests evaluate how clearly a client sees a target at specific distances. Screening for visual acuity is the first test to be performed, as poor visual acuity will affect subsequent tests.
Many people with brain injuries have deficits of visual efficiency. It is also the most frequently overlooked area of vision even though the effects on a patient’s performance can be very significant. If left uncorrected, visual efficiency deficits are very likely to interfere with progress in rehabilitation.
Visual efficiency deficits are often undetected even after a professional eye examination. Therefore, a referral to an eye care professional who is proficient and able to perform the type of testing batteries that detect visual efficiency dysfunction is essential (Scheiman, 2013).
An eye care professional or therapist screening for visual efficiency would first test for near eye alignment. This can be done quickly and easily using a Maddox Rod or a computerized screening tool in the rehabilitation clinic.
Near eye alignment tests for esophoria (where the eye tends to deviate inward, towards the nose), exophoria (tendency of the eye to deviate outward, towards the temples), vertical phoria (vertical eye misalignment), and suppression (when the brain “ignores” the visual image from one eye).
Near convergence is tested using a small target (e.g., the eraser on a pencil or a fixation target from the Northeastern State University College of Optometry (NSUCO) test) and a measuring tape.
The target is held at approximately arm’s distance from the patient’s face and the patient is asked to focus on the target. This will show whether the eyes are aligned or if one or both eyes “float” in, out, up, or down from the target.
The target is slowly moved closer to the bridge of the patient’s nose, and they are asked to signal when they begin to see two targets. When the patient signals, the professional measures and records the distance from the outer eye orbit to the target. This is the “break” point.
Working from the “break” point, the target is slowly moved further from the bridge of the patient’s nose. When the patient indicates that they can again see one target, a measurement is taken and the distance is recorded from the outer eye orbit to the target. This is the “recovery” point. Some literature suggests that this test should be repeated three times and only the last trial distances recorded due to fatigue commonly found in individuals with a brain injury.
Accommodative amplitude is the eye’s ability to switch from close to distant vision. Accommodative amplitude naturally declines with age. Therefore, measurements are compared to age reference norms.
Accommodative amplitude can be measured in the rehab clinic using fixation sticks, an eye patch, and a measuring tape. Fixation sticks resemble white tongue depressors with specificsized letters on them. Each eye is tested separately and measured in diopters, a unit of measurement of the optical power of a lens.
Saccades are the ability of both eyes to rapidly jump from one place to another to bring images onto the most sensitive visual area of the eye: the fovea. Saccades are strongly used during reading tasks and have been linked to attention problems when deficient.
A screening for saccadic dysfunction may be performed in the clinic using the NSUCO test and the Developmental Eye Movement test (DEM).
Pursuits are the ocular movements that hold the image of a target on the fovea when the person or the target or both are moving. Pursuits are crucial skills during mobility and driving. Smooth pursuits can be quickly screened in the clinic using the NSUCO.
Visual field loss is the loss of vision above or below the horizontal or at the opposite sides of the eyes. It is also loss of central vision, or the same side in both eyes. Visual field loss is tested using the direct confrontation technique: the professional sits directly in front of the patient and moves their finger from one side to the other.
Visual processing is a general term for the brain’s ability to analyze and interpret visual information. Visual processing skills include visual discrimination, visual sequencing, visual memory, visual motor processing, visual closure, and spatial relationships (see sidebar above).
A visual processing disorder is considered a deficiency in a person’s ability to effectively use the information the senses have gathered.
Problems with visual processing can be screened using traditional occupational therapy assessments as well as assessments more traditionally used by optometrists. Examples include:
- Gardner Reversal Test: recognition and execution subtests.
- Test of Visual Perceptual Skills (TVPS): 3rd edition determines a child’s visual perceptual strengths and weaknesses.
- Beery Visual-Motor Integration (VMI) test: a convenient and economical way to screen for visual-motor deficits.
Vision touches almost every part of human interaction including functional mobility and activities of daily living (ADL). Occupational therapists have long been involved with the evaluation and treatment of visual perceptual dysfunction. With the Three-Component Model, therapists now have more tools to investigate and treat visual dysfunctions as they relate to performance. Therapists can perform the screening during the evaluation and rehabilitative process.
If deficits are found, a referral can be made to a neuro-optometrist for further assessment and treatment planning guidance. Therapists may work with the neuro-optometrist to implement specific neuro re-education techniques to remediate visual dysfunction and thus improve functional independence.
Vision is an ongoing area of research as it relates to brain injury. With more awareness of the impact of the visual system on functional independence, routine visual dysfunction screenings during brain injury rehabilitation may help clients obtain referrals to vision specialists for remediation and treatment, as well as to understand and manage their functional challenges.
As part of a comprehensive vision evaluation, an occupational therapist completes a vision screening to determine if there are underlying (and often hidden) deficits that require additional attention.
If significant deficits are found, a referral is made to a neuro-optometrist for more extensive testing and treatment. Treatment often includes an occupational therapist implementing neuro-based exercises as prescribed by the neuro-optometrist regarding visual fields, acuity, diplopia (double vision), convergence insufficiency (the eyes do not turn inward to focus on an object), accommodation, and saccades (rapid eye movement).
Occupational therapy also incorporates treatment and retraining for visual deficits into various activities such as activities of daily living, mobility, safety and community re-integration.
Aurelia Wiltshire, OTR/L, CBIS
Aurelia graduated summa cum laude from the Honors Program at Eastern Michigan University in occupational therapy. Aurelia has a special interest and advanced training with the evaluation and treatment of visual disorders after brain injury. She is a Certified Brain Injury Specialist (CBIS), and a veteran of the United States Army.
Definition of optometric vision therapy. American Optometric Association web site. http://www.aoa.org/Documents/optometrists/definition-optometric-vision-therapy.pdf. Accessed July 8, 2013.
Scheiman, M. (2011). Understanding and Managing Vision Deficits: A Guide for Occupational Therapists. Thorofare, NJ: SLACK Inc.
Scheiman, M. (2013, March). Understanding and managing visual deficits, Denver, CO.Suter, P. S. and Harvey, L. H. (Eds.). (2011).
Vision Rehabilitation: Multidisciplinary Care of the Patient Following Brain Injury. Boca Raton, FL: CRC Press. Visual suppression.Medical glossary website.
http://www.medicalglossary.net/Visual_suppression.htm. Accessed July 8, 2013.
What is information processing? National center for learning disabilities website. http://www.ncld.org/types-learningdisabilities/ adhd-related-issues/visual-processing-disorders/information-processing-disorders. Accessed July 9, 2013