Visual Field Impairment
Hemianopsia: Loss of Half of the Visual Field After Stroke or Traumatic Brain Injury
A homonymous hemianopsia is the loss of half of the field of view on the same side in both eyes. It occurs frequently in stroke and traumatic brain injuries due to the connections and wiring of the visual system with the brain. The visual images that we see to the right side travel from both eyes to the left side of the brain, while the visual images we see to the left side in each eye travels to the right side of the brain. Therefore, damage to the right side of the posterior portion of the brain can cause a loss of the left field of view in both eyes. Likewise, damage to the left posterior brain can cause a loss of the right field of vision.
Patient Problems
Patients report running into objects, tripping, falling, knocking over drinks, and being startled by objects or people that suddenly appear in front of them. Patients often loose their place while reading. Patients may become so fearful of falling or running into objects that they may be unwilling to travel or shop without assistance. Panic attacks may even occur when in crowded stores, because hemianopsia patients can easily become lost in crowded areas.
Our side vision allows us to distinguish approaching objects and people in an almost unconscious way. When a moving car passes in front of us, we are not alarmed, because we detected and sensed it was coming. When we lose part of our side vision from a hemianopsia, objects suddenly appear, often startling the patient. The patient may feel unsafe and even overwhelmed in crowded areas
Patients may mistakenly believe that the loss of vision is just in one eye. They may report “my right eye has been bad since the stroke”, while actually the loss has occurred in both eyes, because the damage was in the brain and not in the eyes.
Spontaneous Recovery
Immediately after a stroke or head injury, a dense hemianopsia may be present. In some cases, the field loss may improve and/or resolve in the first few months. Most spontaneous improvement occurs within the first three to six months after the stroke or head injury. After that time period, there is a much smaller chance for improvement or recovery. Unfortunately, most homonymous hemianopsias do not resolve, and thus leave the patient with a permanent disability.
Right versus Left Homonymous Hemianopsia
Because each side of our brain handles different functions, patient’s experience different problems depending on the location of the damage. Patients with a right brain injury may have a left visual field loss, visual neglect, perceptual problems and paresis of a left arm or leg. Patients with left brain injury may have a right visual field loss, language and/or reading problems and right hemi-paresis of an arm or leg.
Additionally in some cases, double vision may occur as a result of the damage to the nerves or centers in the brain that control eye movements. Dizziness may occur when the vestibular balance system is affected. This is common in traumatic injuries when smooth eye movements are disrupted.
Visual Neglect
Visual neglect is a problem that is often confused with homonymous hemianopsia. Visual neglect may occur with or without a homonymous hemianopsia. While homonymous hemianopsia is a physical loss of visual field to one side, visual neglect is an attentional problem to one side of their body. The patient may or may not have a loss of visual field, but due to the visual neglect cannot learn to compensate because they cannot mentally attend to that side. A man with visual neglect may only shave one side of his face. A left visual neglect patient, when asked to recall a description of a well known area, will fail to mention the things to his left side.
Visual neglect is a spatial inattention to one side caused most commonly by damage to the parietal lobe of the brain. While it can happen to either the right or the left, it usually becomes a problem only when the right parietal lobe is damaged and the patient is unable to attend to the left side of the world. Visual neglect usually indicates a worse prognosis for recovery.
It is initially diagnosed by a combination of patient behavior and several basic tests. The most important is the Behavioral In-attention Test (BIT). Visual neglect patients usually benefit from occupational therapy to learn to attend the affected side. Our experience has shown that many patients with visual neglect and homonymous hemianopsia together benefit also from optical aids like the Gottlieb Visual Field Awareness System.
Reading Problems
Because we read left to right, a loss of visual field to the right side creates more problems while trying to read. A patient with a right homonymous hemianopsia will often miss the end of long words and end of lines. A right hemianopsia patient reading the word “chalkboard”, may only see the word “chalk”. Missing the end of long words and the end of lines makes the meaning of the sentence wrong and thus increases patient frustration while trying to read. Additionally, patients have difficulty locating the end of a line of text and may need to use a boundary marker such as a Post-It note or their thumb.
While left homonymous hemianopsia patients have less reading problems, they may initially miss the beginning of a line text. They may have problems moving from the end of one line to the next and often do not move back to the very start of the line. Simple boundary marking with a vertically positioned Post-It note or even a well placed thumb will also reduce this problem.
Treatment centers around three mains areas. First, teaching the patient basic strategies to overcome the hemianopsia. The low vision specialist may teach a number of strategies including Boundary Marking, using a Post-It note or finger to mark the edge of a column of print. It may include Multi-Step Saccades, the process of first looking in the direction of the field loss before trying to search for an object. Special techniques to aid reading may include teaching the patient with a right homonymous hemianopsia (RHH) to look at the last letter of each word rather than the first letter. This allows the RHH patient to see the entire word rather than a part of the word.
Second, new types of optical devices may be used to shift the visual field over to help the patient detect objects to the side of the vision loss. These systems include the Gottlieb Visual Field Awareness System and the Peli Lens and are fit by the low vision specialist. While various types of prisms and mirrors have been used for over eighty years for hemianopsia, it was not until the late 1980s that the Gottlieb Visual Field Awareness System improved the way we treat this problem.
Patients find they can walk about without fear of running into objects. We find their confidence in independent travel increased greatly. The systems are fit on the eyewear lens on the side of the visual field loss. In the past, doctors mistakenly thought that both eyes needed to be fit with prismatic systems. Dr. Peli’s work at Harvard has demonstrated that true field expansion works only when the system is mounted on one eye.
Third, scanning therapy is performed through either the low vision specialist or through occupational therapists to train the patient to better compensate for the loss of visual field. In hospital settings, a Dynavision machine may be used to train scanning. The low vision specialist will also provide a variety of therapies that can be done at home or in-office. Many common activities like table tennis have been found to be helpful to patients learning to scan.
Driving Issues and Homonymous Hemianopsia
Two separate factors determine whether patients may return to driving. First, and foremost, does the patient have the physical, cognitive and perceptual skills to learn to compensate for the field loss? Patients with visual neglect or other visual spatial disorders would not be able to return to drive. Patients with multiple handicaps including paresis of arms or legs in combination with hemianopsia may not be good candidates.
Second, state laws vary in requirements for visual field. Some state may not allow a patient to return to driving despite the patient’s ability to return to safe driving. In Indiana, we first test to rule out those who are poor candidates. Next, patients are usually fit with a visual field awareness system such as the Gottlieb VFAS or Peli lens. Next, the patient undergoes extensive training in scanning with the low vision specialist and/or occupational therapist. Then, the patient undergoes a rehabilitation driving evaluation with a driving rehabilitation specialist including a behind-the-wheel evaluation. If the patient demonstrates an ability to return to driving, behind-the-wheel driver’s training is performed. Upon the completion of training, the patient may be required to pass a BMV driving test.
Hemianopsia is a common condition after stroke or brain injury. It can be quite debilitating and prevent many patients from working, reading and driving. Today, we have many methods available to help rehabilitate these patients. Proper training and the use of optical low vision aids is allowing many to return to a more normal and independent life.