Prevalence, Definitions, and Characteristics
Individuals with visual impairments make up one of the smallest disability areas, or about .04% of the school-age population and .4% of the students served under IDEA (U.S. Department of Education, 2005). Visual impairments range from mild to moderate to severe, and both legal and educational definitions exist. The legal definition includes acuity assessment information, and the educational definition is linked to learning to read. Individuals are classified as legally blind if their visual acuity is 20/200 or less even with corrective lenses and partially sighted if their visual acuity is 20/70. This means a person who is legally blind can see something at 20 feet, which a person with normal vision can see at 200 feet; and a person who is partially sighted can see something at 20 feet, which a person with normal vision can see at 70 feet. Legal classification qualifies individuals for tax advantages and some other legal benefits (Heward, 2006).
Educational definitions are based more on the method necessary for learning to read. For example, many individuals classified as legally blind have some vision and can learn to read using enlarged print. These students are often referred to as students with low vision. Other individuals have such limited vision that they are referred to as totally blind and learn to read using the Braille system (raised dots that are read with fingertips), or by ear using audiotapes. The federal definition is “an impairment in vision that even with correction, adversely affects a child’s educational performance. The term includes both partial sight and blindness” (U.S. Department of Education, 1999).
Visual impairments can be present at birth or acquired later in life. Common causes of visual impairments include glaucoma (excessive pressure on the eyeball), cataracts (clouding of the lens), diabetic retinopathy (lack of blood to the retina), coloboma (parts of the retina improperly formed), retinitis pigmentosa (degeneration of the retina), and retinopathy of prematurity (excessive oxygen to premature infants). Muscle functioning disorders of the eye, such as strabismus (crossed eyes) and nystagmus (rapid involuntary eye movements), also may result in visual impairments.
Individuals with visual impairments can have one or more of a wide range of disabilities, from mild to severe. A common characteristic includes delayed language development due to the restriction of visual experiences (Warren, 1984). Students with severe visual impairments may rely on the tactile and auditory senses rather than the visual sense (Hull, 1990). These students need to hold and feel three-dimensional objects to obtain a sense of the phenomena. If entire objects are held at once, students obtain a complete “synthetic touch” of the article. If objects are too large to be held, however, different segments of the object must be touched sequentially. Using this “analytic touch,” the segmented touches must be recombined mentally to form “the whole.” These skills are referred to as tactile learning, and some research indicates that strategies can be used to teach students with visual impairments how to use and improve their tactile sense of learning (Berla, 1981; Griffin & Gerber, 1982). Because these students may miss opportunities at learning incidentally from seeing everything in their environment, it is necessary to present this information in alternative formats.
Some students with visual impairments engage in such repetitive behavior as head weaving or body rocking. These are known as stereotypic behaviors and are not harmful, except they can attract unwanted or negative attention. Stereotypic behaviors are sometimes addressed by reinforcement, self-monitoring, or physical prompts (Heward, 2006; Ross & Koening, 1991).
Mobility skills vary among individuals with visual impairments depending on the age of onset, degree of severity, and the individual’s spatial ability. Spatial ability appears to affect the mobility access of individuals with visual impairments (Bigelow, 1991). Some individuals with visual impairments learn to walk with canes, although the training can be lengthy and difficult. Some canes have light sensors near the tip that emit sounds when the amount of light changes, indicating shadows or objects in the path ahead. Some individuals learn to walk with human guides and Seeing Eye dogs, although the latter are not usually seen with children (Davis, 2003).
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