During a stroke---also known as a cerebral vascular accident---something happens to stop blood flow to the brain. Lack of oxygen and nutrients can cause visual loss including loss of peripheral vision, which is used to see objects on the side or edges of the visual field. The severity and nature of the loss vary depending on the site of the injury. In addition, blockages within veins and arteries in the eyes can cause "eye strokes."
Types of Strokes that Cause Vision Loss
According to the National Institute on Aging, there are two major types of strokes. The ischemic type is caused by a blood clot or narrowing of an artery or other blood vessel that leads to the brain. A hemorrhagic stroke results when a broken blood vessel causes bleeding in the brain. In addition, blockages within veins and arteries in the eyes can cause "eye strokes." Dr. Chris Knobbe reports that blocked blood flow to the eye can damage vital structures such as the retina and optic nerve, causing decreased or distorted vision. This type of stroke may also be described as "stroke to the optic nerve."
Effects on Vision
Strokes can cause complete vision loss in part of the visual field, or visual neglect---lack of awareness of what is being seen. The most common form of vision loss is called homonymous hemianopsia---loss of half of the field in each eye. An example of this would be loss of vision in the temporal side of the right eye---the side closer to the ear and the nasal side of the left eye---the side near the nose. According to the National Stroke Association, most strokes affect one side of the brain, causing visual loss on the opposite side, and it is rare for both sides of the brain to be affected. Strokes in the occipital lobe---located in the back of the brain---cause visual processing disorders. Optometrists Richard Windsor and Laura Windsor report that eye strokes can cause loss of peripheral vision, usually first in the lower field of view, and that tunnel vision may result in the most severe cases.
Symptoms
Receiving timely medical care for a stroke can lower the risk of vision loss and death. According to the National Institute of Neurological Disorders and Stroke, warning signs include sudden numbness or weakness on one side of the body, confusion, trouble seeing, walking, dizziness, loss of balance and a severe headache. People who have risk factors such as high blood pressure, heart disease, diabetes or a history of strokes should be especially aware of these symptoms. Sometimes, a person experiences a brief episode, called a transient ischemic attack or "mini stroke." These should not be ignored because they are an indication of a serious medical condition that should be treated.
Impact on Function
According to author and optometrist Mitchell Sheiman, people with visual field loss due to stroke may have problems with visual attention to certain areas. For example, the person may not see and eat the food on the sides of the plate. The person may bump into things on the side of the vision loss or be startled when objects suddenly seem to appear on the side that is neglected. People with homonymous hemianopsia tend to bump into things and are uncomfortable in crowds and unfamiliar environments because they don't see things in the peripheral field of one eye. According to Optometrists Richard L. Windsor and Laura K. Windsor, patients who have had an eye stroke may also experience functional problems such as mobility challenges and difficulties walking down stairs.
Treatment
Treatment focuses on compensation techniques, education and counseling, rather than restoration of previous function. Occupational therapists teach patients how to be more aware of the neglected side through activities such as reading or finding objects. A red strip of paper can be placed on the sides of reading materials to train the patient to find the strip before returning to read the next line. Patients are shown how to scan by moving one's head to see needed items in the environment and travel more safely. Optometrists may also provide optical devices to treat hemianopsia and visual neglect. Devices with mirrors help them see movement in a neglected field. Prisms can also increase awareness in the lost visual field. However, there may be distortions that make them a challenge to prescribe and be used effectively.
