DEFINITIONS
Legal Definitions of Blindness
When gazing straight ahead, a normal eye can see objects within a range of approximately 160
to 170 degrees.
Legal blindness is defined as visual acuity of 20/200 or less in the better eye after correction
with glasses or contact lenses or a restricted field of vision of 20 degrees or less.
Visual acuity—the ability to clearly distinguish forms or discriminate among details—is most
often measured by reading letters, numbers, or other symbols from the Snellen Eye Chart.
An individual whose visual acuity in the better eye after correction falls between 20/70 and
20/200 is considered partially sighted for legal and governmental purposes.
Educational Definitions of Visual Impairment
IDEA: “Visual impairment including blindness means an impairment in vision that, even with
correction, adversely affects a child’s educational performance. The term includes both partial
sight and blindness.”
An educational definition classifies students with visual impairments based on the extent to
which they use vision and auditory or tactile means for learning.
- The precise measurements of visual acuity and visual field used to determine legal blindness
have limited relevance for educators.
A student who is totally blind receives no useful information through the sense of vision and
must use tactile, auditory, and other nonvisual senses for all learning.
A child who is functionally blind has so little vision that she learns primarily through the
auditory and tactile senses; however, she may be able to use her limited vision to supplement
the information received from the other senses.
A child with low vision uses vision as a primary means of learning.
The age at onset of a visual impairment affects a child’s educational and emotional needs.
CHARACTERISTICS
Children with severe visual impairments do not benefit from incidental learning that normally
sighted children obtain in everyday experiences and interactions with the environment.
Visual impairment often leads to delays or deficits in motor development.
Some students with visual impairments experience social isolation and difficulties in social
interactions because of limited common experiences with sighted peers; inability to see and use
eye contact, facial expressions, and gestures during conversations; or stereotypic behaviors.
The behavior and attitudes of sighted people can be unnecessary barriers to the social
participation of individuals with visual impairments.
PREVALENCE
Visual impairment is a low-incidence disability affecting fewer than 2 of every 1,000 children in
the school-age population. About half of all students with visual impairments have additional
disabilities.
Types and Causes of VisualImpairment
The eye collects light reflected from objects and focuses the objects’ image on the retina. The
optic nerve transmits the image to the visual cortex of the brain.
Difficulty with any part of this process can cause vision problems.
Refractive errors mean that the size and shape of the eye prevent the light rays from focusing
clearly on the retina.
Structural impairments are visual impairments caused by poor development of, damage to, or
malfunction of one or more parts of the eye’s optical or muscular systems.
Cortical visual impairment (CVI) refers to decreased vision or blindness caused by damage to or
malfunction of the parts of the brain that interpret visual information.
Educational Approaches
Braille—a tactile system of reading and writing in which letters, words, numbers, and other
systems are made from arrangements of embossed six-dot cells—is the primary means of
literacy for students who are blind.
Students who are blind may also use special equipment to access standard print through touch,
reading machines, and prerecorded materials.
https://youtube.com/shorts/CoD9fMk2534?si=jrwIubkOfXeZOc1_
https://youtube.com/shorts/Fv-z_uN6R2w?si=8umWM8eqMeq37RIR
1. BrailleNote
2. Mountbatten Pro Brailler
3. Braille embossers
4. Cuisenaire rods
5. Tack-Tiles® Braille Systems
6. Cranmer abacus
7. Tactile books
https://www.youtube.com/watch?v=WXdDBAHh3eM
Children with low vision should be taught to use their vision as much and as efficiently as
possible.
Students with low vision use three basic methods for reading print: magnification, optical
devices, and large print.
Students who are blind or have severe visual impairments need instruction in orientation
(knowing where they are, where they are going, and how to get there) and mobility (moving
safely and efficiently from one point to another).
1. Orientation and mobility (O&M) instruction
https://www.youtube.com/watch?v=oWUo9AMaS2A
Systematic development of listening skills is an important component of the educational
program of every child with visual impairments.
The curriculum for students with visual impairments should also include systematic instruction in
functional living skills such as cooking, personal hygiene and grooming, shopping, financial
management, transportation, and recreational activities.
