Blindness Basics

A brief introduction to blindness and visual impairment, including locating services for blind infants, preschoolers, students, and adults.


Winning students in the Kentucky Regional Braille Challenge 2011.

Introduction to Visual Impairment and Blindness

Visual Impairment and Blindness

The terms blind and blindness have been modified in our society to include a wide range of visual impairment.

Visual impairment can be defined as any chronic visual deficit that impairs everyday functioning and is not correctable by ordinary eyeglasses or contact lenses. Visual impairment can be mild or moderate but also includes total blindness or functional blindness where no useful vision remains.

In the United States, where normal vision is 20/20, legal blindness is defined as a visual acuity lower than or equal to 20/200 in the better eye, with best correction -or- a visual field of less than 20 degrees in diameter. With 20/200 visual acuity, a person can see at 20 feet what a person with 20/20 vision sees at 200 feet.

Visual acuity is the ability to see fine details. Acuity can only be determined by a doctor and is most often determined by reading lines of successively smaller letters on a chart. Visual field refers to the part of a person's vision that enables them to see what is happening to the side of them.

People are considered totally blind if they are unable to visually detect light of any kind. People are said to have light perception if they can detect light and determine from which direction the light is coming.

The leading causes of visual impairment are diseases that are common in elderly persons, including age-related macular degeneration, glaucoma, diabetic retinopathy, cataracts, and optic nerve atrophy. More than two-thirds of people with visual impairment are older than 65 years of age.

The leading causes of visual impairment in infants and children are retinopathy of prematurity, deficits in the visual centers of the brain, and eye abnormalities such as cataracts and retina abnormalities.

Low Vision and Functional Vision

Low vision means that even with glasses, contact lenses, optical devices, medicine, or surgery, you don't see well. Reading the mail, shopping, cooking, seeing the TV, and writing can seem challenging. Many people with low vision can benefit from learning to use their residual (remaining) vision, often with the help of optical devices and/or large print.

Vision loss can range from mild to severe, but does not include a full loss of functional vision, which is a person’s ability to use their vision in planning and performing daily tasks. Functional visual abilities may range widely for any individual over time due to fatigue, lighting, contrast, glare, and other environmental factors.

Cortical Visual Impairment

Cortical visual impairment (CVI) is a neurological visual disorder. It is the fastest growing visual impairment diagnosis today.

For educational purposes, cortical visual impairment (CVI) is defined as a neurological disorder which results in unique visual responses to people, educational materials, and to the environment. When students with these visual/behavioral characteristics are shown to have loss of acuity or judged by their performance to be visually impaired, they are considered to have CVI.

Here is a more detailed explanation of cortical visual impairment.

Glossary of Eye Conditions

Learn the basics of a wide variety of eye conditions.

Finding Services in Your Area

Funds for Purchasing Educational Materials

The Federal Quota Program provides funds to schools, rehabilitation agencies, and other organizations for purchasing educational materials made by APH. A registration of eligible students working at less than college level determines the amount of money received by each agency. For more information about registering your student, please contact the APH Ex Officio Trustee in your state.

Information for Families

This page contains several links to information useful for families with children who are blind and visually impaired.

More Resources

This resources list contains links to organizations and other information useful for parents, teachers, administrators, rehabilitation professionals, students, and blind adults.

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