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How Does a Stroke Decrease Vision?

Strokes can affect vision in a number of ways, including decreased vision and double vision:

• Decreased vision is caused by damage to the fibers that transmit visual information from the eyes to the brain. This can occur in a variety of locations, since the nerve fibers that transmit vision have a long course from the eyes to the rearmost part of the brain, called the occipital lobe.

• Double vision is caused by damage to nerves responsible for moving the eyes and ensuring that both eyes are aligned (i.e. looking at the same place). In the long term, in some cases, visual field defects from stroke may improve, although there are often permanent deficits. After a stroke, the patient should undergo formal visual field testing by an eye doctor or neurologist to identify precisely the part of the visual field that has been affected. This allows documentation of the deficit and provides a baseline for comparison, should the patient note a change or new visual field loss in the future. While visual fields that have been lost permanently from stroke cannot be returned via any treatment, there are a variety of strategies that enable patients to adapt to their loss of visual field, and to make the most of the vision they do have:

• A primary strategy is learning to move the head and eye more deliberately and frequently, in order to better see the area of visual field that has been lost.

• People who have double vision from stroke may alleviate this symptom by covering one eye or applying opaque tape to one lens of their eyeglasses.

• Prisms can also help resolve double vision. Prisms move or redirect the direction of light entering the eye. They can be ground into the person's eyeglasses or are available as "stick-on patches" (called Fresnel prisms) that can be placed on the eyeglass lenses.

• If the double vision persists and is significant enough, strabismus surgery can reposition the muscles that are attached to the eye to straighten the eye position, improve eye movement, and treat double vision.

• A comprehensive low vision examination, along with optical and non-optical low vision devices and vision rehabilitation services and training, can be helpful for some individuals with double vision or field loss from stroke. To find an International Academy of Low Vision Specialists (IALVS) trained optometrist in your area call 1-888-778-2030.

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