Vision rehabilitation refers to the multidisciplinary effort of assisting those with various degrees of vision loss in coping with the consequences of that loss. To describe vision rehabilitation, the nature of vision itself must be understood.
Vision is the major source of information about our environment.
The eyes alone contribute as much information to the brain as all other organs combined. It is not surprising, therefore, that many people fear loss of vision almost as much as loss of life.
Most people will state that “We see with our eyes.” On closer examination, this is not true. An isolated eyeball cannot produce any vision; our brain, however, can produce exquisite visual imagery in our dreams, without any input from the eyes.
The visual process goes through three distinct stages. Each stage comes with its own specific problems.
• First is the optical stage, where the refractive media of the eye deliver an image to the retina. Familiar problems in this area include refractive errors and cataracts.
• Second is the receptor stage, where the optical image is translated into neural impulses. Age-related macular degeneration (AMD) is a significant problem of the receptor stage, which is becoming increasingly common as the population ages.
• Third are various stages of neural processing, initially in the inner retina, then in the visual cortex, and finally in higher cortical centers, where the visual input gives rise to visual perception and to visually guided behaviors, actions, and interactions.
The most common visual problems vary for different ages. Today, brain-damage-related vision problems (cerebral visual impairment or CVI) are the most prevalent cause of visual impairment in infants and
young children. Given that vision is so important for normal development, vision loss in infants constitutes a developmental emergency and should be detected and addressed as early as possible. When a child does not smile back at the mother, the mother may be inclined to leave the baby in its crib instead of holding him or her to provide extra tactile stimulation to compensate for missing visual stimulation.
At school age and later, visual health is critical because reading becomes important for academic development. For adults, vision is important for maintaining independence in activities of daily living (ADL) and development of vocational skills. For seniors, vision loss may exacerbate other age-related dysfunctions. Studies of the elderly have shown correlations between visual impairment and depression, falls, and reduced longevity. In all of these instances, early detection and early intervention are essential; the primary care physician plays a crucial role in this respect.
Four Aspects of Vision Loss
Vision is a complex phenomenon.
A convenient framework for discussing the various impacts of vision loss is to consider four aspects of visual functioning (Figure 1). First to consider is how various external causes may result in structural changes to the eyes and the visual pathways. For this aspect, the focus is on the tissue; an ocular pathologist is needed to describe the pathologic condition. However, structural changes alone do not determine how well the eyes actually function. Clinicians need to measure organ function, such as visual acuity, visual field, and contrast sensitivity.
FIGURE 1 Aspects of vision loss.
Yet even knowing how the eyes function does not tell us how the person functions. In other words, the abilities of the person to perform tasks, such as reading, mobility, face recognition, and ADL, must be considered. Occupational therapists (OTs) and other rehabilitation professionals work with patients to teach them how residual vision can be used most effectively. OTs also assess the person in a societal context. For example, do the visual changes have an impact on the person’s participation in society, on his or her ability to perform necessary tasks, and on general satisfaction with one’s quality of life? It is clear that to cover all aspects of vision rehabilitation, a team approach is necessary, and that the patient must be part of that team.
A single activity of daily living may cover several of the above aspects. When reading, the aspect of minimum print size falls under organ function (retinal resolution). Reading speed (words/minute) and reading endurance (hours/day) define abilities of the person; reading endurance may be poor, even if reading acuity is adequate. Reading enjoyment, finally, falls under the aspect of quality of life.
It is helpful to draw a line between the organ side of Figure 1 on the left and the person side on the right. On the left side of the diagram, we discuss visual functions, which describe how the eyes function. On the right side, we speak of functional vision, which describes how the person functions in vision-related activities. Medical specialists are well versed in dealing with the left side of the diagram. Yet, the ultimate goal of all interventions is to improve the patient’s quality of life. It is the function of vision rehabilitation to make sure that “eye” doctors become “people” doctors by extending their interest to the right side of the diagram as well.
Comprehensive Vision Rehabilitation
Considering all of these aspects, comprehensive vision rehabilitation involves much more than the patient’s performance on a letter chart and requires teamwork between different professionals who specialize in different aspects of vision loss. All vision loss starts with some medical condition. So, primary care physicians are well positioned to coordinate team activities. Primary care physicians need to be aware of what other team members can contribute and should know where to locate vision rehabilitation resources and to make appropriate referrals. Figure 2 illustrates that comprehensive vision rehabilitation involves much more than does the traditional low vision care offered in the past.
FIGURE 2 Comprehensive vision rehabilitation.
Low vision is a term used to describe individuals who suffer from a visual impairment that cannot be eliminated with refractive correction, yet are not blind. Individuals who suffer from visual impairment from low vision may benefit from vision enhancement, vision substitution, and vision assistance as well as from honing of coping skills.
Low vision is distinct from blindness (i.e., no vision). Blindness differs from low vision in that in blindness, the emphasis of rehabilitation is entirely on vision substitution. Patients with severe or profound low vision may combine the use of some blindness rehabilitation skills with some low vision rehabilitation skills.
Vision enhancement, which is the traditional focus of low vision care, is primarily oriented at improving residual visual function through visual aids, including a wide range of magnification devices.
Additionally, enhancement of contrast, illumination, and filters need to be explored.
Vision substitution expands the options for rehabilitation by optimizing the use of other senses. This can range from using simple tactile markings to sense the position of a stove dial, to devices such as talking books, a long cane for travel, and Braille for reading. Vision enhancement and vision substitution are not mutually exclusive. A patient may use a magnifier to read price tags and may prefer talking books for recreational reading. A patient with retinitis pigmentosa, which causes reduced night vision, may have normal mobility in the daytime and need a cane at night. Digital audio books may have Braille labels.
Vision assistance. A special form of vision substitution involves using the eyes of others. Family members, caregivers, and office personnel should be familiar with sighted guide techniques to effectively assist visually impaired patients with minimal embarrassment. Guide dogs are also a possibility. Using a guide dog requires training of the patient as well as of the dog, so that they can work as a team. Dog users must also demonstrate mastery of long cane travel skills.
Coping skills. How different patients will accept visual aids may differ greatly. It is important to recognize that vision loss often causes a reactive depression. On the one hand, a depressed patient will be less receptive to rehabilitative suggestions. On the other hand, demonstration of rehabilitative success can be a powerful tool to lift a reactive depression and to motivate the patient for further success. It has been shown that the teaching of problem-solving skills may improve the effectiveness of vision rehabilitation.
Many professionals may be involved in vision rehabilitation.
Technicians may prescribe magnifiers, rehabilitation workers may teach daily living skills, and psychologists may address depression. Acceptance of the work of these professionals will be improved if the trusted primary care physician is credited with making the referrals.
Beyond the factors that directly involve the patient, the environment must also be considered.
The human environment is important. As patients go through the stages of adaptation, a supportive home environment is essential. As patients are counseled, it is important to include spouses, children, or significant others to make sure that they understand the condition, know what can be expected, and know how to support the patient.
Answering family and caregiver questions directly is often better than leaving this to the patient, who initially may not have absorbed everything that was said. An overprotective environment, which deprives patients of opportunities to do things for themselves, can be as detrimental as an overdemanding one that puts too much emphasis on the patient’s shortcomings. The same holds true for the work or school environment or for social groups.
Initially, patients often feel isolated and believe that they are the only ones experiencing these problems. Peer support groups can be helpful; in these groups, patients can experience how others are dealing with similar problems.
Finally, the physical environment needs to be considered. An uncluttered environment, where things have a defined, fixed place is helpful because it reduces the need for searching. Good general illumination and task lighting often help, because at higher illumination levels retinal cells that are damaged but not dead can still contribute to vision. Good contrast is important: do not serve milk in a white Styrofoam cup; mark the edges of steps and stairs. The triangles and circles on men’s and women’s bathrooms are designed to be visible for those with very low vision; Braille labels in elevators are useful for people who are totally blind.
How Blind Is Blind?
The most common visual function test is the letter chart, developed by Snellen in 1862. That test determines how large a letter, or other symbol, must be to be recognized by the patient. That size is then compared to the size recognized by a standard observer. If the magnification requirement is 2 ×, visual acuity is said to be 1/2; if it is 5 ×, visual acuity is said to be 1/5, etc. That fraction can be recorded in different ways; in the United States, it is customary to use 20 as the denominator (1/2 = 20/40, 1/5 = 20/100); in the British Commonwealth, 6 is used as the denominator (6/12, 6/30); in Europe, decimal fractions are common (0.5, 0.2).
Those calculations are simple; unfortunately, the terminology used to describe various ranges of vision loss is confusing. Figure 3 shows progressively degraded pictures with examples of the terminology used to describe different definitions of visual impairment. The visual acuity level represented by each picture can be determined from the number of lines that are readable on the low vision letter chart.
FIGURE 3 Ranges of vision loss.
The first picture shows the visual acuity level that is labeled as “low vision” by the World Health Organization (WHO). Although the bottom lines of the letter chart cannot be read, the appearance of the room is near normal. The next picture shows what the U.S. Social Security Administration considers “statutory blindness” for its programs. It is clear that this is far from actual blindness. Other U.S. programs use a different definition for “legal blindness,” and the WHO does not consider a person “blind” until he or she has reached the status of the last picture. At that level, reading even the special letter chart is not possible, but one can still navigate the room. Even this level of visual impairment does not constitute actual blindness.
The widespread use of the word “blindness” is unfortunate, because it cannot be used with modifiers. One is either blind or sighted; one cannot be “a little bit blind.” This black-and-white thinking has hampered the acceptance of vision rehabilitation. Terms such as vision loss or visual impairment are preferred because they can be used with modifiers, including mild, moderate, severe, profound, and total vision loss. Although “legal blindness” and “severe vision loss” (ICD-9-CM) have the same definition, there is a big difference between telling a patient You are legally blind and You have a severe visual impairment. The first statement might be followed by I am sorry, there is nothing more we can do for your eyes; the second statement leads to the question What can be done to help you cope with this problem?
Vision Rehabilitation Techniques and Devices
Having considered the general outlines of vision rehabilitation, some details of rehabilitative interventions can be discussed. Primary care physicians should know what vision rehabilitation techniques are available.
The most commonly encountered visual problems are those involving the optical system of the eye.
Refractive errors are the easiest visual problems to deal with.
Refractive errors can be corrected with glasses or contact lenses, and for those who hate glasses, by refractive surgery. Even if there are other causes of vision loss, determining the best refractive correction is still important.
Uncorrected refractive error is a major cause of visual impairment worldwide. In developed countries, the question may be why people do not avail themselves of the solutions that are available. In developing countries, availability of and accessibility to eye care and to the means for correcting refractive errors often do not exist.
Providing these is a matter of infrastructure, not of individual health care.
Opacities disrupt visual image formation. Cataracts are the most familiar opacity; they can be removed by surgery. Other opacities of a temporary or permanent nature may occur in the cornea, in the anterior chamber, or in the vitreous cavity. Corneal and conjunctival infections may cause corneal scarring, as is the case in trachoma; this condition does not exist in the developed world anymore but is a major cause of blindness worldwide.
Letter chart acuity is a good way to measure optical problems. It should be understood, however, that letter chart acuity only measures the function of the retina where the letter read is projected. Even for a patient with 20/200 acuity, this area of the retina is less than 1° in diameter. For optical problems this does not matter, because foveal defocus predicts equal defocus in all other areas of the retina.
Magnification is the primary way to compensate for reduced acuity. One way to provide magnification is to bring print closer to the eye. For the elderly, this requires reading glasses with extra power.
Alternatively, large print may be helpful. Larger print on medicine labels, as required in several states, can reduce medication errors by the elderly, who often take several medications. Handheld magnifiers are another option; many have built-in LED illumination that provides more light. Video-magnifiers with a table-mounted large screen are ideal for prolonged reading; they can enhance contrast and brightness, while some devices can even read the text out loud. Tablets and smartphone apps can provide similar advantages in a portable form and are increasingly popular as visual aids.
While primitive forms of cataract surgery have existed for centuries, the study of retinal disorders has only been possible since the invention of the ophthalmoscope in 1851. The ability to effectively treat some retinal disorders is even more recent. Important retinal disorders include the following.
AMD is the most frequent diagnosis encountered in any low vision rehabilitation service. Because the condition is age related, its frequency will increase in the future as our population ages. This has caused profound changes in the nature of low vision care. Until the mid-20th century, most low vision care was provided by special education teachers serving young students in schools for the blind.
Today, the majority of low vision patients are seniors. This has resulted in a significant influx of OTs into the field with skills in addressing multiple geriatric impairments. Yet, the needs of seniors to be served still outstrip the available services.
Given that macular degeneration affects central vision and the ability to read, most patients will ultimately seek rehabilitation help. However, if only one eye is affected, AMD may go unnoticed. The patient may only complain when the second eye starts to deteriorate; at that point, the damage in the first eye may be beyond repair.
Therefore, it is useful to ask patients to alternately cover one eye to see whether there is any vision difference between the eyes. If there is, this is a reason for referral.
Glaucoma is another age-related condition. Glaucoma often goes undetected because it causes loss of peripheral vision and affects central vision only in the late stages. Therefore, glaucoma must be sought out, primarily by measuring the intraocular pressure.
Diabetic retinopathy is not limited to seniors. As the incidence of diabetes is rising worldwide, so is the incidence of diabetic retinopathy. Even if treated with photocoagulation, it will cause scattered blind spots throughout the visual field.
There are many other hereditary and nonhereditary retinal conditions that may cause vision loss, but they occur in small numbers. They all require the help of vision rehabilitation professionals to help patients cope effectively.
Scotomata. Whatever the cause, retinal conditions will generally cause localized blind spots (scotomata). Therefore, when retinal damage is suspected, visual acuity alone is no longer a sufficient descriptor of visual impairment, because the retinal area where the chart letter is projected does not predict anything about other retinal areas. In addition to letter chart acuity, the condition of the visual field and the presence of blind spots (scotomata) must be considered. (Figure 4)
FIGURE 4 Ring scotoma.
Figure 4 shows a retinal image, where a word is projected across a ring scotoma that leaves only a small central island of vision. This patient will be able to recognize the central letter, but will not be able to read the word. Clinicians must be careful when providing such patients with magnification, because too much magnification will mean that fewer letters fit into the central area. This example also makes it clear that when retinal involvement is suspected, a reading test may be more informative than a letter chart test, given that reading requires a larger retinal area.
Neural Processing Problems
As stated earlier, the most important stages of the visual process take place after the retinal receptors have translated the optical image into neural impulses.
The first transformations take place in the inner retina. Here, the input from 100 M receptors in each eye is preprocessed and compressed for transmission through 1 M nerve fibers in each optic nerve. The optic nerve fibers do not simply transmit a pixel-by-pixel image, as does a digital camera. Different retinal ganglion cells probably transmit different aspects of the image, such as edges (contrast enhancement), movement, color, brightness, etc. These separate “movies” are transmitted in parallel. At a later stage of neural processing, the different aspects of the image are combined again into a single visual perception.
In the visual cortex, the visual information is further analyzed for shapes and contours. Interestingly, at the first synaptic station in the lateral geniculate nucleus, only 20% of the incoming connections come from the optic nerves; the other 80% come from other cortical centers and probably contribute to filtering based on attention and other factors.
In higher cortical centers, the visual information is further processed. Here, the flow of information is no longer strictly visual, because it is combined with information from other senses. This results in identification and recognition of objects through comparison to stored concepts (through the ventral stream to the temporal lobe of the brain) and in spatial location of an object (through the dorsal stream to the parietal lobe of the brain), which then result in voluntary or involuntary visually guided action.
Our knowledge of these processes is still relatively new. It has been greatly helped by new modalities for neural and retinal imaging.
Today, neural processing problems are increasingly recognized in all age groups.
In young children, CVI is now recognized as the most frequent cause of visual perceptual problems. CVI is often caused by perinatal ischemia, which may cause cortical as well as subcortical changes (periventricular leucomalacia). Because this ischemia is not localized, impairments are often not limited to the visual system. Schools for the blind have increasingly developed into schools for the multiply handicapped.
In contact sports, the results of repeated subclinical injuries are now recognized.
In veterans, traumatic brain injuries may cause problems that may be hard to define. Often visual interpretation and decision making are impaired; oculomotor system problems are often found. Traffic accidents may cause similar damage.
In the elderly, strokes may cause more localized problems and agnosias for specific tasks. In all of these cases, the term visual impairment may be used when visual acuity and/or visual field are impaired. The term visual dysfunction may be more appropriate when the visual input to the brain is normal, but the processing of this information is not.
Patient-Centered Functional Priorities
Vision problems affect all aspects of a patient’s life. It is no longer sufficient for clinicians to determine that nothing more can be done about the causes of vision loss, because much more can be done about the consequences of vision impairment.
To determine the range of services that may be appropriate for an individual with vision impairment, the American Academy of Ophthalmology recommends consideration of the following functional priority areas:
• Reading—for many patients, this is their foremost concern.
• Activities of Daily Living (ADL)—even though reading may be the most prominent complaint, most people spend the larger part of their day performing a variety of other vision dependent activities for self-care and home management.
• Safety—are people at risk for falls? How do they cross the street? Do they drive?
• Community participation—can the individual still participate in community events, including religious gatherings?
• Physical, cognitive, and psychosocial well-being—because many patients with vision loss are elderly, this is an important aspect that should not be overlooked. If cognitive problems exist, it may affect the recommendations to be made.
Based on these considerations, patient-centered priorities can be set and specific rehabilitation goals formulated that reflect the patient’s needs and desires.
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Additional Website Sources
The AFB Senior Site (www.AFB.org/seniorsitehome.asp) contains resources for seniors.
The MDsupport website (www.MDsupport.org) specializes in support and documentation for AMD patients and care givers.
The Lighthouse Guild International in New York (www.lighthouse.org) offers extensive resources for all forms of vision loss.
These websites contain links to many more websites with additional information and often can provide information about local resources.