Sensory impairments may be caused by congenital disorders, diseases, or trauma to the sensory organs of the brain. Disabilities that occur as a result of sensory impairments include blindness, deafness, visual impairment, or hard of hearing.

Blind/Visually Impaired

Visual impairment represents a continuum, from people with very poor vision, to people who can see light but no shapes, to people who have no perception of light at all. However, for general discussion it is useful to think of this population as representing two broad groups--those who are legally blind and those with low vision.

People who are legally blind may still retain some perception of shape and contrast or of light vs. dark (the ability to locate a light source), or they may be totally blind (having no awareness of environmental light). Those with low vision may have problems such as extreme near or far sightedness, no peripheral vision, abnormal sensitivity to light or glare, or night blindness.

People with visual impairments have the most difficulty with visual displays and other visual output (e.g., hazard warnings), utilizing controls where actual operation is dependent on vision (e.g., where eye-hand coordination is required, as with a computer "mouse"), and manipulation (e.g., insertion/placement, assembly).

Many people with visual impairments still have some visual capability and, therefore, can read with the assistance of magnifiers, bright lighting, glare reducers, larger lettering, sans-serif typefaces, and/or high contrast coloring. A small percentage (10%) of people with more severe visual impairments may use braille or large raised lettering.

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Deaf/Hard of Hearing

Hard of hearing is used to describe varying degrees of hearing loss. Deaf persons can not hear or understand spoken words. They may respond to loud noises, but are unable to understand speech without visual cues. Usually, a person is considered deaf when sound must reach 5 to 10 times louder than normal speech (at least 90 decibels) to be heard, and even amplified speech cannot be understood.

Persons who are hard of hearing have some ability to hear and understand the spoken word, although some words may not be clear. They may, instead, be guttural and distorted, making it difficult or impossible for them to be understood. To communicate, people who are deaf or hard of hearing may use hearing aids, sign language, lipreading, notetakers, and/or TTYs (text telephone).

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