NeuroRehabilitation An Interdisciplinary Joumal

ELSEVIER

NeuroRehabilitation 6 (1996) 203-212

Enhancing decreased sight of patients with traumatic brain injury Paul B. Freeman*, Randall T. Jose 206 Westbury Dr., Coraopolis, PA 15108, USA

Abstract Vision loss is often a complication of a traumatic brain injury (TEl). To maximize rehabilitation of a person with a TBI, the professionals who coordinate and carry out therapeutic activities should be aware of the impact impaired vision can have on over all processing. This article will address how the low vision examination and treatment process can be an invaluable adjunct to a rehabilitative therapy program.

Keywords: Tramatic brain injury; Low vision; Low vision devices; Visual impairment; Low vision examination; Vision rehabilitation

1. Introduction

The opportunity to return to a meaningful quality of life for patients suffering from neurological insult due to traumatic brain injury (TBI) has significantly improved in recent years. Although TBI results from an outside force impacting upon the neurological system, neurological insult also includes injury from cerebrovascular accidents, degenerative diseases such as multiple sclerosis, neurological impairment from toxic substances, infections to the central nervous system and pathology which can lead to an altered state

* Corresponding author, Tel.: + 1 4127414380; Fax: + 1 412 2629448.

such as tumors. Tremendous strides in the medical/surgical care of these patients results in a higher incidence of survival [1], but many are left with physical, and/or mental losses that are sometimes extremely profound. Vision loss is a frequent complication of a traumatic brain injury and can also complicate the evaluation of a patient's residual capabilities. Unfortunately, most TBI insults occur retro and/or caudal to the orbit and therefore cannot be diagnosed through conventional means. Based on the area of the brain which has been injured, one can note specific central or peripheral vision involvements [2-4]. If there is an interruption/blockage of the flow of blood from the carotid artery, the following can occur -

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transient blurring of vision, loss of vision in the ipsilateral eye, or a homonymous visual field loss [5]. An involvement of the pons or midbrain (ie. vertebrobasilar artery insufficiency) can create double vision [6]. Cerebral hemisphere involvement can result in cortical blindness or homonymous visual field losses [7]. In addition to losses in central and peripheral vision, some patients also suffer from palinopsia (visual perseveration) [8]. In rare situations, an inexplicable awareness in the blind area has been demonstrated as well [7]. In addition to these sight/visual impairments, many patients who have suffered closed head injury may also have signs of alexia, aphasia, ataxia, apraxia, hemi-neglect, etc. [5]. As innovative rehabilitative treatment modalities continue to improve [1,9,10], the role of properly evaluated vision is vitally important to the success of the rehabilitative process. Vision deficits along with other injuries need to be assessed individually and in relation to one another because they can affect the patient's rehabilitative process which will have an impact on the patient's future quality of life. Vision is usually an integral part of the activities involved in a typical rehabilitation therapy program. Low vision services can be of significant help to the rehabilitation therapists in designing an effective rehabilitation plan for the patient, helping to differentiate vision disabilities from other physical or sensory disabilities [9,10]. In some situations, an accurate description of the patient's functional vision (ability to visually perform specified tasks) is not available to the physicalor occupational therapist. Therefore, impaired vision can sometimes be misinterpreted as a cognitive impairment especially when compounded with communication dysfunctions. When observing patient's responses to specific directions or tasks, the therapy team may prescribe unsuitable or inadequate therapies or may modify goals for the patient, while in fact the individual simply did not see well enough to respond appropriately. For instance, if a therapist presents a task in an area of field loss unknown to the therapist, such as handing materials from the left side to a patient with a left homonymous hemianopsia, this lack of response could be mterpreted as negkct, inatten-

tion, unawareness, etc. If the details of the task are too small for the patient's visual acuity or a reading task cannot be performed because it can't be seen, this may be interpret~d as a loss of cognitive ability. Also, it is not uncommon for an individual's glasses to be destroyed in an accident and not replaced due to the initial attention to more significant life-threatening concerns. Provision of something as simple as a spectacle prescription, especially a bifocal, can make a significant difference in the accuracy of the patient's visual responses in the rehabilitation program. A thorough low vision assessment can provide the therapy team with information on many aspects of vision. By coordinating historical information with an appropriate low vision examination, the clinician can identify the basis for optical/non optical and visual functional intervention. This intervention can augment the remaining sight both in acuity and processing, regardless of the genesis of the loss. This can then be integrated into activities of daily living which are dependent upon sight or visual integrative processing. These results can also be used to determine whether the limitation of performance experienced in therapy is due to sight loss, poor visual physiological processing, or a severe perceptual or cognitive deficit. 2. The low vision exam The low vision evaluation is an optical and functional evaluation to determine whether the vision the patient has retained can be improved. This evaluation can be divided into three segments, all on a continuum and all integrated with one another. It includes exploration of sight (optical and non-opticaI), physiological skills (convergence / divergence, accommodation, pursuits and saccades) and perception. Eyesight describes the neurologically challenged patient's level of visual resolution or localization. The descriptor for this is visual acuity. The fractional number i.e. 20/20, 20/30, etc. serves as the basis for determining the amount of sight information that passes through the optics of the eye and the neurological pathways, ending at the visual and other related cortecies. It is the

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basis for making environmental modifications, i.e. large print, close working distance, etc. for the patient. If sight is the determining cause of decreased performance, the low vision clinician can make recommendations for the therapist to either modify the position of the task, enhance the size of the task, or work with low vision optical devices to bring the visual parameters of the task into line with the individual's visual capabilities. This clinical data along with the information from other rehabilitative evaluations can be used to establish an Individualized Vision Rehabilitative Program for the patient with TBI. This will result in a more productive, less frustrating therapy [11-14]. Physiological processing describes the triad of eye functions (convergence/divergence, pursuits/saccades and accommodation) and their impact on the visual system's ability to effectively and efficiently transfer sight information to the visual cortex. This physiological processing allows the patient to gather information about the environment under clear, single, simultaneous binocular vision (or clear single vision if monocular). An intact physiological processing system should permit the patient to derive information which should lead to efficient perceptual processing. Perceptual processing describes information being processed through the integrated sensory motor visual system. It is how the patient interprets and interacts with the world and forms the basis for higher level concept formation and development. Low vision evaluations are done most appropriately by an optometrist or ophthalmologist who has had extensive background in the assessment of the visually impaired and can translate that information into functional goals. The emphasis is on obtaining data both subjectively and objectively to serve as the basis of potential for enhanced visual capabilities and ultimate visual processing. In conjunction with a low vision evaluation protocol, a thorough ocular health examination must be done to determine the integrity of the anatomical areas related to the system in question, i.e. the external eye, cornea, lens, iris, vitre-

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ous, retina, optic nerve, and the tracts leading to the cerebrum and cerebellum. Because each of these segments of the evaluation could be voluminous, this article will address and describe the first part of the continuum of the evaluation, i.e. central and peripheral eye sight enhancement. Included will be an overview of treatment options, describing optical and nonoptical low vision systems and their properties. 3. The evaluation process Patients with decreased central visual acuity or loss of peripheral vision must first be evaluated so that baseline information can be obtained. These acuities, both central and peripheral, can change within the first 6 months to a year and a half depending on the extent and complexity of both the anatomical and neurological damage [5,7]. Therefore, initial information and subsequent intervention may need to be modified over time. However, this information will serve as a starting point for prescribing low vision devices and for monitoring progress as both time and treatment progress. 4. Case history The low vision clinician must determine the patient's visual capabilities as well as disabilities. Recommendations will be made regarding strategies to enhance visual performance and assistive technology (optical low vision devices) prescriptions. Since the major purpose of the low vision examination is to integrate these recommendations and prescriptions into the total rehabilitation process, the low vision clinician must take and review the extensive case history related to the vision loss. The low vision clinician must know the underlying medical cause of the vision loss; the extent of the traumatic injury, co-morbidities; past and present physical rehabilitation programs; and the socialj economic consequences of the physical, mental and/or visual losses [15]. It is important that realistic concerns be elicited through an extended functional history. Also, a systems review may bring out other problem areas that can complicate visual functioning (depression, pain, limits of motion, tremors, diabetic

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complications, etc.). Ultimately, this extended history will help define specific problem areas to be addressed, suggest the need for specific testing, and will aid in the planning of the overall patient rehabilitation program. This is also the time the patient can become comfortable with the low vision clinician, reducing any anxiety or unrealistic expectations from the low vision examination process. 5. Distance visual acuity After a thorough case history, the clinician will take a measurement of distance visual acuity. Acuity information helps define discrimination and identification or localization at a specific distance. These measurements are defined by the familiar Snellen acuity number, or the ability to locate a specific size target at a specific distance ie. localization acuities. The better the retinal image, the less confusion for the patient when trying to work on perceptual and physiological processing. With the TBI patient (as well as most visually impaired patients), this acuity test is measured with high contrast vision charts. Low vision charts can vary and can utilize single letters, numbers or symbols, depending upon the patient's cognitive level [16,17]. Examples of these charts are the HOTV acuity system, the Feinbloom distance acuity chart, the LH Symbol Visual Acuity test (Lea Hyvarinen, M.D.) The clinician usually starts the testing at 10 ft instead of the typical 20-ft test distance. In many cases, the clinician may even have to work with patients at a 5-ft distance to obtain a visual acuity. This can be particularly true when evaluating patients with perceptual dysfunctions, specifically those having difficulty with 'visual noise' or figure-ground. In addition to modifying the test distance, the acuity procedure may be changed from a verbal response to having the patient point to a symbol on the chart, match a chart symbol, or even blink in response to the symbol. If the patient cannot respond to symbols, preferential looking techniques (Teller acuities, Bailey PL cards) like those used with infants can be modified to use with this

population. Also, optokinetic nystagmus (OKN) responses can be used as a gross judgement of vision. Finally, visually evoked potential (YEP) measurements can be used to obtain an objective estimate of the patient's visual acuity [18-20]. 5.1. Refraction (objective measurement)

Initial distance visual acuities are compared to distance visual acuities after a thorough refraction has been performed to determine if an improvement in eyesight can be accomplished with a modification in conventional lens prescription. A refraction is a standard method of objectively determining if lenses (eyeglasses) can improve sight acuity by focusing light accurately on the retina (macula) for optimum resolution. Utilizing a retinoscope is the mainstay of this objective measurement. 5.2. Subjective

When interposing lenses in front of the patient, the clinician hopes for some response to determine and confirm the best prescription for the most accurate sight. If acuity cannot be improved to the level necessary for specific task activities, those visual acuities will act as a basis for a distance and/or near low vision device after a low vision refraction is performed. A low vision refraction is performed on a visually impaired individual when conventional techniques have been tried and found to be unsuccessful. The objective use of radical retinoscopic techniques (performed at unconventional distances from the patient), and subjective using a trial frame, trial lenses, telescopes and other optical devices are explored. Target positioning, lighting and other visual modifiers are used to help determine: (a) Whether a conventional lens can be appropriately modified to improve qualitative, not necessarily quantitative measurements. (b) If a conventional lens prescription in combination with a telescope, microscope, non-optical device, electronic form of magnification, or field enhancement system can be used to improve sight/visual performance.

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6. Near visual acuities Acuity measurements are taken from small and large distances. These acuities are measured using the same array of charts and optotypes as described for distance acuity measurements. This testing is usually performed at a 13- or 16-inch working distance, but can be done closer if necessary to elicit a response. There is a mathematical relationship between distance and near acuities so that this measurement also acts as a confirmation test of distance acuities. As with distance acuities, these tests can be accomplished both with and without verbal responses. For the therapist, the distance at which the test must be given to elicit a response can sometimes be as important for the rehabilitation plan as is the actual size of the symbol seen by the patient. 7. Visual field testing Visual field testing is very difficult to perform and to obtain reliable results on these individuals. These tests can be performed with electronic/ computerized instrumentation. This testing is used to verify the presence or extent of a suspected field loss based on the pathology, site of brain injury or functional observation [21,22]. However, sometimes a simple confrontation test can provide gross information about the existence of a field restriction. For example, if a patient responds to a target only when the midline is crossed into the left field, then a right hemianopsia can be assumed. Visual field neglect may be a little harder to measure and should be reviewed with the neurologist, physiatrist or neuro-ophthalmologist. It is important to note that poor field testing techniques can lead to a misdiagnosis of neglect. A good clinician will repeat field testing several times before making any significant recommendations regarding compensatory training, therapy or field expanders. In addition to these basic tests, the low vision examination can also include a measurement of contrast sensitivity function, integrity of central field (Amsler grid) and color vision. The results of these tests will help the low vision clinician better describe the patient's sight and should help ex-

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plain some of the patient's performance and behavior on visual tasks. 8. Physiological assessment While this article will not concentrate on physiological processing, it is important to know if the patient has single binocular (or monocular) vision. Sometimes spatial awareness will be confusing if· there is a constant diplopic image or variable binocular status due to an ocular motor misalignment. Often, the clinician will only be able to measure the physical misalignment of the eyes and be able to provide an educated guess as to the patient's compensation or response to the alignment problem. In these situations, the clinician may work with the therapist to provide situations that could substantiate a binocular dysfunction to determine if the patient is confused. In some instances, a patient may be biocular, using one eye for some tasks and the other eye for other tasks, i.e. one eye for distance, one eye for near. The total data from the examination can now be used in conjunction with information from other disciplines to establish preliminary goals for the visual component of the rehabilitation process. The type of optical and non-optical treatment is also formulated at this time. Some of the more typical optical options offered in a low vision program are described in the following section. However, with the TBI patient, the low vision clinician is often challenged to be creative beyond these examples. 8.1. Low vision treatment options

In most instances, when a decrease in central/peripheral acuity or field is established, there exists a low vision device/training technique that can be used to enhance sight or compensate for a field loss. Thus the phrase 'nothing can be done', is inappropriate and misleading. However, what is important is that the rehabilitation team relate the acuities to the patient's goals to determine which low vision prescription will ultimately benefit the patient. The types of devices that are typically used to help individuals

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enhance decreased visual acuities or peripheral loss can be divided into near devices, distance devices and field enhancement devices. These alone or in conjunction with rehabilitation therapy will be reviewed so that a basic understanding of available devices can be appreciated. 9. Optical devices Near devices which magnify are primarily designed for routine daily activities such as reading, crafts, etc. Most individuals spend considerable time enjoying these activities, both in rehabilitation as well as in their own environments. For example, cooking requires a number of sight demands. One needs to select the food which is to be prepared. Instructions including appropriate ingredients and proportions need to be seen, the oven or microwave has to be set, and a visual determination of completion of the task is required. Then, placing the food onto a plate and seeing it to eat it in a culturally acceptable way is important. All of these seemingly simple tasks require a great deal of sight and physiological integration and processing. Any visual enhancement in either or both areas is of value. By enhancing sight, devices for near are a start in assisting these patients. These devices can be subdivided into the categories of head mounted systems (microscopes), handheld and stand systems (magnifiers) and electro-optical magnifiers. 9.1. Headmounted systems

Patients who require a reasonable field of view with hands free can benefit from microscopes. Microscopes are typically the optical systems used to magnify a task. These are systems that are designed for viewing targets at an extremely close proximity, i.e. from 10 inches to approximately 0.5 inch from the face. This is in contrast to the usual 13-16 inch distance one typically functions when doing a near activity. These lenses can be designed as full field reading lenses, half lenses, or bifocal lenses. The concept for these systems is based on magnification by proximity (relative distance magnification). This magnification is realized by moving a target as close as is necessary to

the patient to achieve detailed viewing. The theory behind the use of the microscope, then, is that once the target is placed at the appropriate distance, these microscopic lenses act to properly focus light so that accommodation (focusing) needed for the task is not attempted. For example, if materials held normally at 16 inches ( + 2.50 diopters of accommodation)! cannot be seen unless magnified eight times, the options for the target are two. The target size can either be enlarged eight times (relative size magnification) at the 16-inch distance or can be moved closer to the patient eight times. To accomplish this, the materials would have to be moved to approximately 2 inches ( + 20.00 diopters of accommodation). The actual lens power would be modified based on the patient's refractive error and accommodation, and the type of prescription to be incorporated into the final system [23]. The above is an example of a very strong microscope which would be used monocularly. With most high powered microscopes, monocularity is encouraged to decrease discomfort from attempting to be binocular at such a close range. However, there are some low powered prismatic microscopes with dioptric powers of + 12.00 diopters or less that could potentially be binocular, given reasonably equal central or peripheral acuities. The major drawback of a microscope is the close eye to task working distance. However, with appropriate guidance, a patient can use a microscope efficiently and comfortably. For example, this requires acclimating the neck and shoulder muscles to new positions and methods of performance. This emphasizes the importance of working with the therapist as a critical component of success. 9.2. Hand magnifiers

Hand magnifiers are typically used for individuals who need to hold materials at a reasonable

lAccommodation is 'the adjustment of the eye to attain maximal sharpness of retinal imagery for an object of regard' (Dictionary of Visual Science). The measure used to describe the amount of adjustment is the diopteL A diopter can be converted to inches or any other measure to accurately define where a target can be held to be seen clearly.

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working distance from the face, and are primarily used for spotting or short-term viewing. The dioptric power of a hand magnifier can be the same as a microscope, the difference being that there is a handle rather than a frame surrounding the lens. However, just as in a head mounted microscope, the task must be placed at the focal length of the lens for optimum magnification. Therefore, the lens to object distance for a + 20.00 diopter lens would be 2 inches regardless of whether it was handheld or head mounted. The difference would be the distance from the face. For example, when shopping, a patient can learn to magnify print on packages, cans, etc., placing the hand magnifier at the appropriate distance from the object. The hand magnifier would be held 2 inches from a package at arm's length. If the same lens was placed into a frame the target would still be held 2 inches from the lens, but because the lens was being worn, it would be 2 inches from the face as well. There are a few disadvantages to hand magnifiers. For one, a patient does not have both hands free. Also, when a patient suffers from tremors or other motor disabilities, materials may not remain in focus, causing possible frustration and confusion. Another disadvantage is that, functionally, hand magnification is typically limited to Sx. Finally, the field of view decreases as the system is held away from the face, affording less information to be viewed at one time. Because of this, many patients start with a close working distance with a large field of view, then modify their working distance in an effort to modify the field of view based on the target and surrounding information. An interesting phenomenon of a hand magnifier is that if held correctly (material at the focus of the lens), the actual retinal image size remains consistent at all distances.

9.3. Stand magnifiers Stand magnifiers can also have the same power as head mounted microscopes and hand magnifiers, but have the addition of legs or platforms instead of a frame or handle. Today, most stand magnifiers are adjustable so that the materials viewed can be at the focal length of the lens,

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creating magnification concepts similar to a hand magnifier. However, if the system is not focus able, the patient is then required to use accommodation or a reading lens. This makes the optics of this system somewhat more complex than the other systems, as the marked magnification on the system may not be the true magnification. An advantage of a stand magnifier is the stability of the optical system. This would be important for those with motor difficulties. For example, someone with tremors could place the stand on a page when reading, thereby minimizing the movement of the system. Additionally, many stand magnifiers have an internal lighting system, using either standard light, halogen, or other forms of lighting. This is important for patients with contrast sensitivity problems or for those who require high levels of illumination. The primary disadvantages of a stand magnifier is its bulkiness and, as in a hand magnifier, limited power and field of view for practical functioning.

9.4. Electro optical systems Electro-optical systems involve electronic circuitry, the most common of these being a closed circuit television. The magnification concepts are actually a combination of proximity (linear) and relative size magnification. By combining these two forms of magnification, 60X magnification can be achieved. The materials being viewed are placed on a moveable platform so that the information is available to a camera. This is often very valuable for TBI patients who have deficient ocular motor skills. (For those who have fine motor dysfunctions, electronic tables are available to help move the material.) The camera then magnifies the image onto a television monitor permitting high levels of magnification without losing contrast or light. Images that are projected onto a screen can be black on white, white on black, or in some situations color. The advantages of these systems is the amount of high contrast magnification, the viewing distance one can achieve, and the potential to use both eyes simultaneously. The disadvantages are reliance on a power source and

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bulkiness, although these issues are being addressed.

there are some specific vocational tasks for which these types of modifications are useful.

9.5. Distance devices

9.6. Field enhancement systems

Distance devices such as telescopes offer the viewer the opportunity to see objects in the distance with greater clarity but within a specific and reduced field of view. For example, when shopping, a telescope can allow the patient more independence and encourage executive functioning for establishing a location and then making appropriate decisions on what to do. Telescopes can be prescribed as handheld telescopes, ring mounted telescopes, clip-on telescopes worn over eyeglasses, or telescopes integral to the lens or frame. Because of the optics, movement is exaggerated through the telescope. Also, spatial perception is altered so that everything appears much closer due to an increase in the size of the image. In addition, by eliminating peripheral cues when viewing through the telescope, the patient must scan to appreciate the total picture. Because of these concerns, the practical magnification of a telescope is 6X. However, there are powers up to 18X. The obvious advantage of these systems is magnification. There are some disadvantages, however. The telescope as an optical system loses some light at its optical surfaces so that those who need an abundance of light may suffer from a decrease in contrast even though the targets are enlarged. Another drawback is that one cannot continuously view through a telescope while walking. A telescope is designed for spotting. Also, because of the very nature of a telescope, it can be a cosmetic concern to the user. However, some new telescopes are miniaturized or even fit behind spectacles so that they are more acceptable in appearance. Finally, an advantage/disadvantage of a telescope is that it can be modified for reading by either using a lens placed on the objective side of the telescope or focused for close working tasks. The advantage of this is that it extends the working distance from the patient to the task, and the disadvantage is that the field of view becomes considerably smaller than a comparably powered microscopic system. However,

Patients with field losses tend to be in jeopardy of safe travel due to loss of peripheral information. These patients need to be cued to be aware of this lost information. This can be done by either. scanning techniques or field enhancement devices. However, field enhancement systems do not actually enhance the visual fields. They optically allow the patient to find information in the lost visual field more efficiently [24]. Mirrors and prisms are field enhancement systems used to encourage the patient to be more aware of a hemianopic or sector field defect [25-28]. The advantage to these systems is that they encourage scanning techniques and help the patient become more aware of the field deficit. The primary disadvantage is that they modify the perception of where objects are in the environment. Therefore, they require extensive training and strict supervision for safe and effective use. Another way of field enhancing is through minification by using concave lenses or reversed telescopes [29-31]. These systems are designed for enhancing symmetrical constrictions of visual fields of 20 degrees or less by compacting information into a very small area. However, there are spatial distortions with these systems which can further confuse the visual spatial orientation of the neurologically challenged patient. 10. Conclusion There are many methods of enhancing central and peripheral sight. However, any patient who is introduced to these systems must be taught to use them appropriately, as they are very task and environmentally specific. While appearing straight forward in nature there are many subtleties that need to be addressed. For example, a lens for reading may not necessarily be the lens appropriate for writing. A system for viewing television may not be the same as a system used for driving. A field expander may be good for travel but may confuse a patient when reading. Also, when and

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where the task is performed is important. Will the patient be doing the task while seated or when mobile, and under what lighting conditions? Therefore, a team approach between the rehabilitation therapist/optometrist is critical to the efficient and effective use of these low vision devices. The road to the successful use of these devices is an arduous one. However, with guidance and perseverance many individuals can achieve success and use that success to enhance their activities of daily living and mobility. Throughout the process, the clinician should not forget the psycho-social concerns of the patient and family, so that the patient can ultimately return to a semblence of visual and functional normalcy [32,33]. References [1) [2)

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Holm C. A simple method for widening restricted visual fields. Arch Ophthal 1970;84:611-612. [31] Brilliant R. Horizon on amorphic lens. Rehabil Optom 1984;2(1): 14. [32] Krantz J. Psychosocial aspects of vision loss associated

with head trauma. J Am Optom Assoc 1992;63(8):589-591. [33] Marks M, Sliwinski M, Gordon W. An examination of the needs of families with a brain injured child. NeuroRehabil 1993;3(3):1-12.

Enhancing decreased sight of patients with traumatic brain injury.

Vision loss is often a complication of a traumatic brain injury (TBI). To maximize rehabilitation of a person with a TBI, the professionals who coordi...
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