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VISION & BALANCE PROBLEMS FOLLOWING ACOUSTIC NEUROMA SURGERY
By Dr.Jeffrey H. Getzell

In April 1990 I had a large acoustic neuroma removed. Following the surgery I had problems with my balance that I was able to resolve to a great degree by putting myself through a regimen of visual training. Occasionally I still notice that I drift to the right when walking if I am not attentive to the information directly in front of me, but that is always easily remedied. I have treated a number of patients following acoustic neuroma surgery over the years and they are always fascinated to find out that their vision problems are not only real but treatable and not something they will have to learn to live with for the rest of their lives.

Having lost the balancing center in your ear, you are told to rely on your vision to help you maintain balance. Yet you don’t seem to be able to control your eyes and you are uncertain as to what you are actually seeing, and you are having difficulty maintaining your balance. In order to understand what is happening , and what to do , it is important you understand there is a difference between “vision” and “sight.”

When vision is discussed, most people (including many doctors) use the word interchangeably with sight. What’s the difference? Sight defines how clearly and how far one is able to see an object. You may be familiar with the term “20/20”. All this means is that you able to see the size of letter on the eye chart that you are supposed to be able to see from 20 feet, for the short period of time required for the test. However, a growing number of optometrists – called behavioral or developmental, optometrists – have found vision to be a much more complex and all-inclusive function than sight alone.

It is a person’s vision that concerns the behavioral optometrist. Especially after an acoustic neuroma where your visual input is more important than ever – you may be able to see that eye chart, but, like myself, balance is off because visual input isn’t being processed correctly; or you may have difficulty judging distance, bump into things, experience loss of place, headaches or poor comprehension with reading.

After an acoustic neuroma you may be told that your vision is fine because you have passed the eye exam, yet you continue to struggle. A regular eye exam tells us nothing about how one processes the information that has been visually taken in, or how their vision is affecting their balance or how they move and think. In order to determine if there are any visual deficiencies or dysfunctions interfering with someone’s balance, thinking and movement more in-depth testing is required; this type of testing is generally only done by a developmental or behavioral optometrist.

Behavioral optometry became a formalized field of study in 1928, when the Optometric Extension Program Foundation, Inc. (OEP) was founded. The OEP has published post-graduate papers, holds post-graduate courses, seminars and congresses, etc., on topics related to behavioral optometric care. Behavioral optometry is the study of the role of vision in balance, posture, movement and thinking.

In the late 1960’s, Colin Trevarthan, a neuroscientist at Harvard University, researched vision and its connections in the brain, and found that physiologically and anatomically there were actually two-vision systems. These are called the ambient and focal vision systems – two terms he was the first to coin. Trevarthan thus discovered the anatomical and physiological evidence to support what behavioral optometrists had known clinically for years.

The focal vision system is located in the occipital cortex of the brain in the back of the head and includes sight or visual acuity. This system, which is concerned with detail and identification, governs the visual ability to make small discriminations between similar shapes, words and letters (e.g., a diamond vs. a square; “but” vs. “bat”; “h” vs. “b”), and answers the question, “What is it?”.

But it was Trevarthan’s discovery of the ambient vision system, located in the mid-brain where visual fibers meet with neurological fibers from the postural and balance centers, which gave a scientific and anatomical explanation for behavioral optometrists’ assertion that vision governs posture, balance and movement. The ambient vision system, is how we answer the question “where is it?”, and directs our body to come to terms with the task at hand: where and how we sit, how we hold our head when we read or position our hands when we write. It also sets up a three-dimensional framework in space so we can zero in and answer the question “what is it?” – which is the focal vision system, which has already been discussed.

So, while many ophthalmologists and optometrists concentrate their focus on their patients’ visual acuity (how clearly they can see the eye chart), behavioral optometrists help patients develop, remediate and rehabilitate visual function (including acuity). It is logical then that their evaluation procedure is more all-inclusive and time-consuming than the typical exam, which is limited to eye health and acuity. An average behavioral vision evaluation usually requires an hour of testing, as well as thirty minutes or more to explain the findings to the patient and/or parent.

This evaluation is both analytical and performance-based. During the analytical portion, the behavioral optometrist tests for distortions in the patient’s vision system. The doctor starts by measuring ranges of visual comfort and clarity, as well as the patient’s ability to see comfortably and clearly while looking far away and up close.

During this part of the evaluation, the behavioral optometrists also looks at the patient’s ability to process information and maintain focus effortlessly for long periods of time. Children and adults who have limitations in this area will fatigue or tire easily, “tunnel”, confuse similar looking words, and may see the world in small chunks or segments, resulting in reading slowly or with frequent pauses.
It is the performance portion of the initial behavioral exam that differs most radically from the traditional sight exam. Here the behavioral optometrist observes the patient’s behavior while performing specific tasks; e.g. observing how the patient is able to follow a moving target. The inability to do this is often an indication that the patient will also skip words, lose place, fatigue with extended reading and have to go back and reread in order to understand. Similarly, the ability to follow a moving object while questions are being asked or directions given, shows how well the person’s vision system is working at higher levels of thinking and movement. Vision problems in this area will frequently result in distractibility. This is often referred to as a learning related vision problem; and may be misdiagnosed as ADD or ADHD.

Similarly, if the patient is not able to reproduce simple geometrical shapes in a given pattern, there will probably also be trouble with forming letters, spacing letters, and keeping them on the line, as well as organizational problems, such as not being able to do math problems in an orderly fashion on the page.

If the patient cannot hop or walk across the room in a straight path while keeping the eyes fixed on a target, he or she will most probably also be awkward and clumsy at tasks requiring movement and coordination, and may bump into things, spill food, have difficulty pouring, and knock things over. He or she may also need to hold onto the wall for guidance when walking down a hallway.
The relationship between vision, posture and balance is critically important for patients who have neurological impairment – e.g., cerebral palsy, multiple sclerosis, strokes , brain tumors and injuries – because these people often have involvement of the mid-brain area where the vision, posture and balance systems meet. However, it is also crucial to people who have behavioral and learning problems, which might result in clumsiness as well.

After this evaluation, the behavioral optometrist will determine what can be done to help the patient function more effectively on the job, studying or in performing daily activities. Often therapeutic lenses are recommended, along with a program of visual training to develop, remediate or rehabilitate visual function. During the visual training program the patient is taught how to develop the visual skills needed to meet the demands of their daily life.

Vision problems can be very debilitating. They can severely compromise our enjoyment of reading, create anxiety when we have to make judgements when driving or stepping on or off a curb, or make us feel unstable walking through a crowded room. Behavioral Optometric rehabilitation allows us to help many people return to a normal life.

Behavioral Optometry, Ltd.

Jeffrey Getzell, OD, FCOVD, FCSO

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