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Vision Loss

Vision loss is also referred to as visual field loss, an area within the field of vision that a person cannot see. Specific visual field loss conditions are differentiated based primarily on the size and scope of the visual disturbance. A stroke that occurs in the left hemisphere can inhibit the ability to see the right visual field of each eye, while right hemisphere stroke can impair the left visual field of each eye.

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Different types of visual field loss:

  • Hemianopia means blindness in one half of the visual field. The most common form of this is homonymous hemianopia, which means that the vision loss is on the same side of each eye. Research shows that eight to ten percent of stroke survivors have homonymous hemianopia.
  • Quadrantanopia means blindness in a quarter of the visual field.
  • Scotoma refers to an island-like area of blindness, typically smaller than hemianopia or quadrantanopia.
  • Tunnel vision means that peripheral vision is lost. Medically, this is known as bitemporal hemianopia. The outside half of the visual field in each eye is blind.

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The goal in developing a treatment strategy for vision loss is to expand the visual field. Treatment can be broken down into three different categories:

  • Optical therapy is also known as vision field relocation. Mirrors or prisms are used to displace images from the blind area to the seeing side. Optical therapy does not restore vision loss, but can increase the visual field by 20 degrees.
  • Eye movement therapy may also be known as visual search training or saccadic training. As the eye moves across the page while reading a book, a person with vision loss will naturally move the eye into the portion of the visual field which he cannot see. As a result, he will lose his place while reading. Eye movement therapy trains the eye muscles to compensate by only moving within the portion of the viewable visual field, resulting in improved reading ability and speeding up the ability to take in all surroundings.
  • Visual restoration therapy is a controversial six-month therapy program designed to expand the visual field. Flashing lights on a computer screen stimulate partially functioning neural cells at the edge of the blinded area within the visual field. Studies have shown an increase of five degrees in the visual field, but critics speculate that visual improvements are a result of eye movement toward the flashing lights. The therapy is customizable to each patient.

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Complete recovery from vision loss is rare, so adapting to life is often necessary.

Using prisms and optical therapy can be a permanent solution to partially expand the visual field and improve balance, mobility and reading, allowing for increased quality of life.

The typoscope, also known as a reading shield, is a management tool for hemianopia. This tool is a solid piece of cardboard or plastic with a rectangular slit. When the typoscope is placed over text, the reader can frame a specific section and eliminate the glare that comes from the surrounding page’s white space.  Typoscopes can be purchased or handmade.

The U.S. has established vision standards for driver’s licenses but these standards vary by state. Check your local department of motor vehicles for specifics. Standards usually include:

  • No double vision
  • Ability to differentiate the colors red, green and yellow
  • Visual acuity of 20/40 in each eye or 20/30 in one eye
  • Visual field width of 70 degrees or more

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Content Updated: August 2012

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