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Legal Blindness

Normal vision, or 20/20, means a person sees the smallest letters or pictures on an eye chart when standing 20 feet away from the chart. Some people cannot see normally,  even with glasses or contacts,  because a medical condition affects their vision. These people are called visually impaired or visually handicapped.

If a visual handicap limits vision to 20/200, or one-tenth of normal, a person is legally blind. Legally blind does not mean totally unable to see. Someone legally blind cannot see the line below the second big E at the top of the eye chart. People with 20/20 vision but less than 20 degrees of side vision can also qualify as legally blind. People who see well with only one eye are not considered legally blind, nor are people who wear glasses to see better than 20/200.

Most legally blind people function quite well, especially if they have been visually handicapped since childhood. Older children and adults with visual handicaps may need magnifying lenses for reading and telescopes for distance viewing. People with very poor vision may need to learn Braille and walk with a seeing-eye dog or a cane.

Young children with visual impairments should have help from a teacher of the visually impaired and should be evaluated for developmental problems by professionals experienced with visual handicaps. Parents may need to be advocates for their child to obtain needed services through the school system.

Visually handicapped people of all ages benefit from social service, occupational therapy, and orientation and mobility training. Many new devices are available to cope with vision loss, including books on audio tapes, scanners that turn print into Braille, watches that can be “read” with the fingers, and talking computers and calculators.  (See our web site section on Low Vision for a list of resources for people who are visually handicapped.)

Eye Conditions

Color Blindness

Color blindness (color vision deficiency) is a condition in which certain colors cannot be detected. There are two types of color vision difficulties: inherited (congenital) problems that you have at birth, and problems that develop later in life.

People born with color vision problems are unaware what they see is different from what others see unless it is pointed out to them. People with acquired color vision problems are aware that something has gone wrong with their color perception.

Congenital color vision defects usually pass from mother to son. These defects are due to partial or complete lack of the light-sensitive photoreceptors (cones) in the retina, the layer of light-sensitive nerve cells lining the back of the eye. Cones distinguish the colors red, green and blue through visual pigment present in the normal human eye. Problems with color vision occur when the amount of pigment per cone is reduced or one or more of the three cone systems are absent. This limits the ability to distinguish between greens and reds, and occasionally blues. It involves both eyes equally and remains stable throughout life.

There are different degrees of color blindness. Some people with mild color deficiencies can see colors normally in good light but have difficulty in dim light. Others can’t distinguish certain colors in any light. In the most severe form of color blindness everything is seen in shades of gray.

Except in the most severe form, color blindness does not affect the sharpness of vision at all. It does not correlate with low intelligence or learning disabilities.

Most color vision problems that occur later in life are a result of disease, trauma, toxic effects from drugs, metabolic disease, or vascular disease. Color vision defects from disease are less understood than congenital color vision problems. There is often uneven involvement of the eyes and the color vision defect will usually be progressive. Acquired color vision loss can be the result of damage to the retina or optic nerve.

There is no treatment for color blindness. It usually does not cause any significant disability. It can, however, prevent employment in an increasing number of occupations.

Change in color vision can signify a more serious condition. Anyone who experiences a significant change in color perception should see an ophthalmologist.

Eye Conditions

Low Vision

Low Vision

Over three million people in the United States do not have normal vision even with corrective lenses. If ordinary eyeglasses do not provide clear vision, one is said to have low vision. This should not be confused with blindness. People with low vision still have useful vision that can often be improved with low-vision devices.

book_magglassLow vision can result from birth defects, inherited diseases, injuries, diabetes, glaucoma or macular degeneration. Although reduced central or reading vision is most common, a person can have low vision in their side (peripheral) vision, or a loss of color vision or contrast sensitivity.

Low vision devices or aides are available in optical and non-optical types. Optical devices use lenses or combinations of lenses to provide magnification. They should not be confused with standard eyeglasses. There are five main kinds of optical devices: magnifying spectacles, hand magnifiers, stand magnifiers, telescopes and closed-circuit television. Different devices may be needed for different purposes. If possible, try the optical device before purchasing it and be sure you understand how to use it.

video_monitorThe simplest non-optical technique is to bring the object of interest closer. Non-optical low vision devices include large print books, check writing guides, enlarged phone dials, talking appliances (timers, clocks, computers), and machines that scan print and read out loud.

Government and private agencies have social services available for people with low vision. For more information, contact the following resources:

WISCONSIN SERVICES

  • All Saints Healthcare, Racine
    Rehabilitation Services – Low Vision Therapy
    (262)- 687-6780
  • Eye Institute, Milwaukee
    Low Vision Services
    (414)-456-7957
  • Badger Association of the Blind and Visually Impaired, Inc.
    (414)-258-9200
  • Wisconsin Department of Health & Family Services
    Office for the Blind and Visually Impaired
    (888)-879-0017

NATIONAL SERVICES

  • American Academy of Ophthalmology Web Site
    www.aao.org
  • American Foundation for the Blind
    (800) 232-5463
  • National Association for Visually Handicapped
    (212) 889-3141
  • National Library Service for the Blind and Physically Handicapped
    (800) 424-8567
  • Lighthouse International
    (800) 334-5497
  • National Eye Institute
    (301) 496-5248
  • Prevent Blindness America
    (800) 331-2020
  • Visions/Services for the Blind and Visually Impaired
    (212) 425-2255

Veterans may contact the Visual Impairment Services coordinator at their local VA facility.

Courtesy of the American Academy of Ophthalmology.  Reprinted from Patient Education CD Personal Eyes and Ophthalmic Images, with permission of the American Academy of Ophthalmology, copyright 2003.  All rights reserved.  Users of this website may reproduce one (1) copy of this for their own personal, noncommercial use.  All Internet, web or electronic posting or transmission is not permitted.

Eye Anatomy

Eye Anatomy

Eye Cross Section

anatomy

Eye as a Camera

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Eye Muscles, Front View

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Eye Muscles, Side View

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Eye Conditions