How Brain Injuries Affect the Visual System
Posted on Tue, Oct 30, 2012 @ 08:00 AM
Say “brain injury” to someone, and they immediately think of memory loss as the result. But vision problems also affect a significant amount of brain injury patients, which should come as no surprise considering 40-50% of the brain is involved in vision.
It’s important to note that we’re not just talking about traumatic brain injuries (TBI). A brain injury can also be a stroke, tumor, aneurysm or due to a degenerative neurological condition. Here are some general statistics to give you some perspective on how widespread brain injuries are:
- An estimated 1.7 million people suffer a traumatic brain injury (TBI) annually. – The Center for Disease Control and Prevention
- The United Cerebral Palsy Foundation estimates that nearly 800,000 children and adults in the United States are living with cerebral palsy.
So out of these cases, how many result in vision problems?
It’s hard to put a
specific number on percentages. Dr. Gregory Goodrich, a supervisory research psychologist assigned to the VA Western Blind Rehabilitation Center, notes, “For TBI in general, the literature says 20-40 percent of people with brain injury experience related vision disorders; however, the exact prevalence is not known.”
What we do know is that in many of these cases, eye muscles or the nerves controlling the eye muscles are damaged, resulting in problems with teaming, movement and focusing of the eyes. In addition, since vision connects almost everywhere in the brain, many other types of vision problems can occur after a brain injury.
(Check out this video for an insightful interview with Dr. James Kelly on TBI)
Causing a Wide Range of Vision ProblemsThe brain is amazingly complex, and as you’d expect, the effects of a brain injury can vary widely. Here are a few examples of patients we’ve helped, each of whom experienced a slightly different vision problem:
- A man was an extreme skier. On one daring ski run, he lost his balance and tumbled hundreds of feet down the face of a mountain. Since then, in addition to other injuries, he’s experienced constant double vision.
- A woman experienced a stroke and subsequently a hemianopsia, which is the limiting of your visual field. Most typically with strokes, the hemianopsia can occur with both eyes and is on one side of the visual field or the other. If you think of your vision as a big balloon, it’s as if one side of the balloon is pushed in toward the center. Some patients are very aware that they are “missing” part of their visual field and some are not. In this case, the woman constantly ran into door jams, objects, and people on one side, but not the other.
- Another stroke victim experienced visual space perception problems. She described that she has to carefully think about where she wants to go and how she wants to get there. She then said she has to “throw her vision out there” so she can actually move. As you can imagine, this takes a great deal of effort and is very fatiguing.
The varying nature of the symptoms in these stories come as no surprise to us, considering the wide-range of issues that can occur with a brain injury. The most common visual symptoms include:
- Double vision
- Poor eye tracking ability
- Difficulties with shifting gaze quickly from one point to another
- Focusing
- Loss of binocular vision (eye alignment)
- Eye strain
- Fatigue
- Glare, or light sensitivity
- Inability to maintain visual contact
- Headaches
- Blurred near vision
The extent of the injury can also impact a person’s visual information processing ability. This can cause the following symptoms:
- Spatial disorientation
- Shifts in ability to judge location of objects
- Difficulties with balance and posture
- Poor depth perception
- Memory loss
- Poor handwriting
But why do these spatial perception issues occur? For that, let’s take a look at how the visual system works, including the “Ambient Pathway.”
The Damaged “Ambient Pathway”
How is a person’s visual system affected by a brain injury? We’ll try and break it down without getting overly technical:
In essence, a brain injury often affects your ability to judge where you are in space. Developmental optometrists refer to this as “general spatial orientation.” Where you are in space can include walking down a hallway, climbing steps, or driving a car. It has to do with your ability to visually process the world around you.
This visual processing is organized by two systems:
1. The focal pathway – This is related to central vision, and is how you see clearly.
2. Peripheral vision and the ambient process – When aiming your eyes at a specific object, the peripheral vision allows you to see other objects. Peripheral vision is a result of a visual process called the ambient process. It takes information from a variety of sources and uses them for orientation and movement. It contributes to balance, movement, coordination and posture.
In essence, peripheral vision and the ambient process provide information on where you are in space, and the focal pathway tells you what you are looking at.
With a brain injury, the ambient process is often compromised, and your visual system can’t match information with your focal pathway and other elements of the visual system.
When these systems are affected, this influences not only balance and movement, but also perception of space and the ability to process information.
For example, a person may experience difficulty in an environment with a lot of visual stimulation, such as a grocery store. He or she may feel overwhelmed and have problems finding an object on a shelf. In addition, dizziness and nausea may be experienced in trying to do so.
Movement in a crowded environment can become quite difficult, too, and a person may experience vertigo.
Prevalent issues, Recommended Treatments
Here are three of the most common issues we see and our typical treatments:
Visual Field Loss
What it is: A person becomes blind to a portion of their field of vision. This is often the result of nerve damage. Typical terms that are used to describe visual field loss:
- Hemianopsia: If you think of your visual field as being a pie, with hemianopsia half of the “pie” — or visual field, either vertically or horizontally — is gone; you cannot see in that area.
- Quadranopsia: a quarter of your visual field is lost.
- Homonymous hemianopsia: the same half of the visual field is lost in both eyes.
Remember that even though the description is two dimensional, the visual field loss is in three-dimensional space.
What it impacts: Typically results in a person becoming clumsier, bumping into objects, falling, and even being struck by other objects. It can be much worse if the person has visual “neglect” in which they have no idea that they are missing the visual field.
How it is typically treated: The prescription of yoked prism lenses and optometric visual therapy for ocular scanning can help patients identify objects in the affected field, and react and process at an improved functional level.
Double Vision
What it is: A person’s binocular vision is affected, and the brain is unable to combine the images seen by each eye into one single image. This is referred to as “seeing double.” The double vision could be for far vision, near vision or both and may be constant or part of the time.
What it impacts: Results in poor depth perception and visual confusion. If the double vision is constant, it can affect almost every daily activity that requires vision including walking, reading, computer work, household chores, etc.
How it is typically treated: The best outcome in treating double vision is restoring a person’s binocular vision. Treatment usually includes optometric vision therapy to help the person relearn how to use both eyes together again. When that is impossible, treatment might include using prisms or some form of segment occlusion to help the person function as best as possible.
Egocentric Shifts
What it is: An egocentric shift involves a change in how your ambient process provides information about orientation relative to your sense of center.
What it impacts: A patient will experience a “visual mismatch,” and may walk as if the floor is tilted. The patient may have very subtle or extreme changes in posture as they try to align their “center” with the world around them.
How it is typically treated: Optometric vision therapy, special occlusion and/or yoked prisms are used to help re-establish correct orientation and sense of center.
Note that patients with brain injuries will also be concurrently receiving multi-disciplinary treatment including services from physiatrists, occupational therapists, physical therapists, speech and language professionals and many others.
Evaluation and Treatments Involve a “Neuro-Optometric” Approach
These types of vision problems can’t be detected with a mere Snellen eye chart. This may be referred to as a “Neuro-Optometric” approach, because it not only accounts for eye health and visual acuity, but also visual-motor, visual perceptual and visual disorientation difficulties. Your evaluation and treatment will generally include:
Step 1. An initial assessment, in which skills that affect both your ability to see and identify an object, as well as your sense of where you are in space, are thoroughly evaluated among many other visual skills.
Step 2. Once the issue has been assessed, treatment may include special glasses prescriptions for therapeutic purposes or to compensate for the problem, syntonics (colored light therapy—affects the nervous system) and/or optometric vision therapy. If optometric vision therapy is prescribed, patients may come in to the office weekly combined with home activities or may be prescribed more of a home based program with regular follow up (typically 1 to 3 months).
Success rates will vary widely, as is typical with any type of brain injury. However, it has been our clinical experience that most patients can experience some significant relief from symptoms and a return to normal or close to normal functioning is sometimes possible. Note that the severity of symptoms is not always an indicator of the success that is possible.
Naturally, the first step toward relieving any kind of vision problems, whether they’re caused by brain injuries or otherwise, is to receive a Functional Vision Test.
Photo by: bradleygee
The Vision Therapy Center has helped over 2,000 people overcome vision problems since 1995, and has Wisconsin vision therapy offices in Brookfield and Madison.