Visual Impairments

Clinical Definition

A clinical definition, which emphasizes a medical characterization of the visual impairment, has limited use in education because it does not address how the disability affects the individual's education. However, a clinical definition is essential to qualify individuals with visual impairments for government-supported benefits, such as social security or other federal programs. The legal definition of visual impairment demonstrates these points: It includes assessment of visual acuity (a measurement of the clarity and sharpness of vision) and the visual field (a measurement of the area that can be seen from a central or peripheral point). Normal acuity is 20/20 (i.e., a person can clearly see at 20 feet what should normally be seen at that distance). A person is considered legally blind if central visual acuity is 20/200 or less in the better eye with corrective eyeglasses (i.e., the person must be as close as 20 feet to see what a person with normal vision can see at 200 feet). A person also is considered legally blind if a defect shrinks the widest possible diameter of the visual field to 20 degrees or less in the better eye (i.e., the amount a person can see peripherally when the eye is focused on a single point). In addition to the blindness, there is a clinical definition for low vision. Individuals who have low vision have a visual acuity ranging from 20/70 to 20/200 in the better eye with correction.

Functional Definitions

A visual impairment occurs when an individual has decreased vision, regardless of the severity of the vision loss. Individuals with mild vision loss may not be significantly affected by the impairment. However, those individuals with moderate to severe vision loss may require considerable support in order to perform daily tasks such as moving around their homes or the school or community. Whatever the degree of vision loss, these individuals may need accommodations such as Braille, large print for reading, high-power magnification devices, mobility aids, or other environmental devices to properly function in their surroundings. Thus, visual impairment may refer to low vision or to blindness. People with low vision use their sight, but they experience difficulties in completing typical tasks. Additionally, these individuals require compensatory strategies, assistive technologies, and modifications to the environment to address their needs. On the other hand, blindness means the individual has no functional vision, although he or she may have the ability to recognize the presence or absence of light.

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