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The effects of MS on vision and hearing.

Introduction

Each spring, Paraplegia News presents a special report on multiple sclerosis (MS). In the past four years, specialists in various fields and people with MS have addressed diverse issues, including personal experiences, coping skills, patient/doctor relationships, and last year, sexuality.

This year our two authors are experienced professionals dedicated to comprehensive, maximal rehabilitation of people with illnesses that affect the senses (vision, hearing, taste, touch, smell). Their articles present information about the effects of MS on vision and hearing and the relationships among the various senses and the motor system.

MS is often associated with vision problems, but the authors' insights into sensory and motor relationships are likely to be new to most readers. Their work is already changing the nature of rehabilitation in certain kinds of disabilities and holds the promise of new strategies for multidisciplinary teams.

William V. Padula, O.D., F.A.A.O., is a neuro-optometrist and chairman of the Neuro-Optometric Rehabilitation Association, International. He is director of the Low Vision Clinic at the Rehabilitation Center in New Haven, CT, and is also a consultant to the National Academy of Sciences and director of Vision Research at Gesell Institute of Human Development. Dr. Padula practices with Shoreline Vision Rehabilitation Associates in Guilford, CT, and presently consults internationally with the Zhongsham Eye Research Center in Canton, China, and the Centrol de Aprendija in Cuernavaca, Mexico, as well as with numerous hospital programs for those with traumatic brain injury.

In addition to serving on numerous boards and holding various state and national professional offices, Dr. Padula is the author of many articles and the book, A Behavioral Vision Approach for Persons With Physical Disabilities, published in 1988 (see bibliography). The following article by Dr. Padula draws on his research and practice experience with people of all ages and diverse backgrounds.

Our second author, William R. De l'Aune, Ph.D., is chief of the Auditory Research Section of the Research and Development Center at the VAMC in Decatur, GA. He trained in experimental psychology and audiology and has particular expertise in psychoacoustics and the neurophysiology of sensory systems. He has been a researcher in sensory impairment for 26 years, with a major interest in the use of hearing by people with visual impairment.

Dr. De l'Aune's article begins with a summary of findings from studies conducted in the past ten years by various researchers. He then applies his findings and expertise with sensory perception to the motor system and speculates on the implications of existing knowledge for rehabilitation strategies. Please note that Dr. De l'Aune's article closes with an invitation to contact him if you can contribute additional professional or personal MS experience related to his article.

Both of these articles remind us that ongoing research continues to yield positive results in the present and to hold promise for future increase of our rehabilitation potential.

MS:THE CONNECTION

BETWEEN VISION,

BALANCE, AND

POSTURE

The diagnosis of multiple sclerosis and a measurement of a person's ability to function can be considered in terms of what limitations the person has. Let us consider two commonly occurring limitations and then think about how they are related to each other:

* Muscle spasms (moto spasticity)

* Visual problems

Muscle Spasms

People with MS may have muscle spasticity, rigidity, an inability to coordinate movements, and difficulty fine-tuning and maintaining balanced and erect posture. The motor condition resulting from MS is caused by neurological changes such as nerve degeneration. Medications can be used to reduce the spasticity in some cases.

Visual Problems

Visual problems can incldue blurred vision, double vision, difficulty with eye-muscle control, problems with tracking (following a moving object with the eyes), and an unstable peripheral visual field (more about that later). There may be nystagmus, a regularly repeated jerking of the eyes to the sides or up and down. These changes are related to the fact that MS frequently causes a degeneration of the nerve fibers that connect to the eye (the optic nerve).

So both problems are related to nerve degeneration. However, the relationship of the visual system to the motor system--and balance, posture, and movement--is often overlooked. When we analyze what vision is and how it relates to specific motor functions, we can consider possible means to improve motor performance by affecting vision.

What is Vision?

Vision is not just "eyesight." It is a dynamic, interactive process of motor and sensory functions. Vision uses the eyes to help organize and control movement and to stablize what we see around us. Our visual process is very much a part of our motor system, and vision helps us with our balance, posture, and movement.

There are more than 1,900,000 nerve fibers leaving each eye. (That is approximately 70% of all the sensory nerve fibers in the entire body.) Two thirds of a billion electrical nerve impulses per second received in the brain are related to visual processing. Therefore, a significant amount of information is received by the brain through the eyes each second. "Seeing," or imaging, our visual world occupies a major part of our attention and thinking.

A common misunderstanding is that "seeing" delivers information to the brain, much like a computer. But seeing is much more complex. It is related to movement, posture, and in general, our motor system. Because our brain usually coordinates these functions so rapidly and so well, most people take vision for granted. Only recently have we begun to learn more about how these processes are connected.

We have to kinds of eyesight (see Figure 1). The first is "focal sight," which carries images through the central part of the eye. It helps us see details, and it is actually a fairly recent development in the millions of eyars it has taken our human visual system to develop through evolution. Through the focal process, we develop "fixation" (the ability to look directly as something).

"Peripheral eyesight," also called "ambient process," is delivered to the brain from the peripheral or outer circle of the eye. Peripheral vision affects our awareness of where we are in space and where things are around us. This part of our vision is very important to the body's motor system.

Vision and Learning

Even before babies are born, they use the connections among their senses to adjust their bodies to gravity and their mother's movements. In the last months prior to birth, the baby's movement causes its eyes to move.

After birth, vision is mostly the ambient kind. This is because babies need to learn to organize their movements--how to hold up their heads and how to move their arms and legs. Ambient vision helps them do that because it is linked to the brain's centers for balance, movement, and coordination.

As children grow older, their focal vision matures, and they can center in on details. Focal vision also helps refine the movements a baby has learned. The interchange between the two kinds of vision continues throughout the child's development into adulthood.

MS, Vision, and Movement

Why it is important to understand this development? Our senses and motor systems are closely connected in complex ways. Our brain matches information from our senses and motor system so that movements can be coordinated. If any of the individual senses have a deficit or any part of the motor system is restricted, either of these limitations will affect the other.

When the neuromotor system becomes impaired, as with MS, the ambient visual system can no longer match information with the motor system as it once did. New information coming into the brain from both can become distorted. The brain attempts to make sense of the information it is getting from both systems, but because of the impairment, things "seen" in the environment may be distorted.

For example, a person may see the floor as tilting upward, rather than as it really is. Then he or she will tend to lean backwards when sitting or walking in order to feel perpendicular to the floor. Of course, this causes difficulty with balance in walking, because the weight is shifted backward. Posture may also be distorted by the combined muscle spasticity, rigidity, and backward lean. The person involved often is not aware of distortion because there is no basis for comparison, but some may be aware of distortion or changes in balance.

Another thing our ambient vision and motor system tell us is where the midline of our bodies is in space. Normally you know where your midline is, front to back (anteriorly and posteriorly) and from side to side (laterally). But if either your ambient vision or your motor system is impaired, your sense of midline may be shifted from front to back or from side to side. Then your sense of space becomes distorted. Several conditions may be responsible for this kind of midline shift: MS, strokes, traumatic brain injuries, cerebral palsy, and other disabilities.

People who are blind in one eye or have one-sided paralysis may think the midline is more to one side. They often lean away from the affected side, thus increasing the effect of the paralysis.

Treatment

We tend to think about our individual sensory processors (our eyes, ears, nose, tongue, mouth, and fingers) as separate systems. so we have highly specialized professions to treat each of them. We have optometry and ophthalmology for vision, audiology for hearing, and specialists in olfaction for smell. We usually get effective treatment for a specific sensory organ, but this specialized approach is not effective in dealing with sensory-motor problems.

Neuro-optometric

Rehabilitation

People with MS who have visual midline shift with neuromotor dysfunctions can benefit from a neuro-optometric rehabilitation evaluation. This exam is very different from a routine eye exam. Its purpose is to analyze in depth the profound relationship between the ambient visual process and the neuromotor system.

Through the neuro-optometric evaluation, prescriptions can be made for various types of lenses and prism glasses that can counter the effect of visual midline shift. Frequently, the neuro-optometrist will prescribe specially designed glasses called "yoked-prism" glasses, which will have the effect of shifting the visual midline. In some cases glasses can dramatically improve posture and balance. In the case of the "tilted room" example given earlier, yoked-prism glasses can caused the floor to be seen as level. The person will then shift his/her weight in the necessary direction and will have better balance. If the midline shift is to one side, yoked prisms can be used to shift the midline and prevent leaning.

Yoked-prism glasses are usually prescribed for therapeutic use in short time intervals each day. The doctor may also recommend these prisms during physical-or occupational-therapy sessions. The yoke prisms have been found to be effective in assistig therapists in maximizing the effect of their own clinical therapies. The yoke prisms should be used only under the direction of a neuro-optometrist.

Conclusion

Neuro-optometric rehabilitative services can greatly benefit those who have MS. Visual midline shifts that affect posture, balance, and movement may be addressed. Treatments developed through neuro-optometric services can add to the rehabilitative multi-disciplinary services that are available for people who have multiple sclerosis. Through neuro-optometric services, rehabilitation can be more complete. The effects of other therapies can be maximized to promote better balance and coordination, and the broad goal of increased self-confidence can be furthered.

MS AND

HEARING

Does MS affect hearing? For many years, audiology (hearing) tests have been used in comprehensive examinations of MS patients. In the 1980's, a number of studies suggested that one-sided (unilateral) loss of hearing $Idid$N occur, although rarely, in relapses of MS. High-technology studies indicate this loss is related to the effects of MS on the auditory nerve, which connects the ear to the brain.

Early in the illness, however, some kinds of diagnostic tests whos auditory changes so subtle that patients are not even aware of any hearing differences. Let us consider some of those diagnostic tests and speculate as to what the changes may tell us.

Speech Discrimination

Although most MS patients can hear tones of various pitches at normal levels, many cannot tell when a tone goes "sharp" or "flat"; they are "deaf" to the pitch changes. What does that mean in everyday living? Because our ability to understand human speech is related to our ability to hear pitch changes, this may explain why some MS patients have trouble understanding words in conversations and may complain about other people mumbling.

Auditory Spatial Analysis

Dr. Padula's article talks about how our senses and our motor system are related to our ability to gather information about the space around us. MS patients have trouble telling where sounds are coming from ("localizing' the sound). The effect? Someone with MS may be able to tell whether the sound is coming from the left or right, and whether it is from in front or behind, but cannot judge the height of the source of the sound.

Some MS patients also have difficulty "tracking" sound. With normal hearing, we can locate the source of sound through two mechanisms. The first has to do with intensity (essentially, loudness). If you think about being between two stereo speakers and having someone shift the balance so that one speaker is louder, you know that the sound "moves" to the loud side. People with MS continue to have this specific mechanism for tracking sound.

The other mechanism people with normal hearing use concerns the fact that unless a source of sound is exactly equally far apart from each ear, the sound will reach each of our ears split seconds apart. the brain then uses that information to help locate the source of the sound. This is actually the way you can selectively listen to a single person at a cocktail party, by the location of the sound (not the person's voice quality). MS patients experience a loss of this "time-of-arrival" ability to locate sound. So one mechanism works but the other does not, and the task of locating things by sound is much more difficult.

Nystagmus, Balance,

and the Vestibular System

Most of us know that one part of the ear, the vestibular system, is related to balance. It also seems that it is connected to the "jumpy" eye movements of nystagmus. Vestibular tests accurately indicate a diagnosis of MS. And dizziness is one of the major symptoms of MS.

Acoustic Reflex

Tiny muscles in your middle ear are connected to bones in your inner ear. If a loud sound occurs, these muscles tighten, probably to protect your delicate inner ear. This reflect seems to change in MS patients. It is not clear yet what the consequences of that loss are.

What Do These

Findings Mean?

First we need to note that human beings have a wonderful mechanism for adapting to the loss of most functions: redundancy. This means that there is often more than one way the body carries out a function. In those instances when one aspect or sense fails, we can still accomplish the same task by having other aspects or sense function better. This sometimes allows some rather spectacular results in the rehabilitation process. A totally blind person can cross the stre safely by paying attention to traffic sounds. Someone with profound hearing loss can learn to understand speech by visually reading lips.

But the losses are still losses. If we think about the test results we described earlier, we realize that each of the changes is subtle and that each one separately may not seem to create a major problem or even be noticeable. But when they are put together with the losses in other sensory systems, their overall effects may become magnified. The total effect is greater than we might expect from the individual changes.

For example, inability to hear pitch changes, and therefore difficulty in understanding speech, may be slight. Add to that an impaired visual system and the possibility of not being able to use lip reading or see facial expressions and body language to understand what is being said, and the combined losses in hearing and vision may severely compromise the ability to communicate with other people.

Some problems with communication may be the result not only of motor problems in producing speech but also of not being able to hear the words so they can be modified. (There is no feedback). In another example, the inability to tell where sounds are coming from may not seem like a serious loss. But if your vision and your balance systems were also impaired, and you did not have your hearing 'anchors," you would have to work much harder to walk or stand upright without falling. Overall, it is likely that it would be more difficult to accomplish demanding tasks. It is more expensive in terms of the amount of effort it takes to do things (i.e., someone with MS must work harder and longer to get the same results as someone without this problem).

Up to this point, research has given us considerable information we can use to help in accurate diagnoses, but a great deal more exploration of how these findings affect people's functioning and their lives is possible and desirable. It would be particularly valuable to learn more about the rehabilitation potential of al MS-related sensory losses.

References

Liebowitz, H.W. and R.B. Post.

"The Modes of Processing Concept and Some Implications." J.J. Beck (Ed), in Organization and Representation in Perception: Hillsdale, NJ. Erlbaum, 1982.

Padula, William. A Behavioral Vision Approach for Persons With Physical Disabilities, Optometric Extension Program. Santa Ana, CA, 1988.
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Title Annotation:includes related article on multiple sclerosis; Special Report; multiple sclerosis
Author:Larrimore, Pat; Padula, William V.; De l'Aune, William R.
Publication:PN - Paraplegia News
Date:Apr 1, 1991
Words:2926
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