1. LEGAL DEFINITION OF BLINDNESS
based on measurements of visual acuity and field of vision:
visual acuity the ability to clearly distinguish forms or discriminate details at a specified distance is measured by reading letters, numbers, or other symbols from the Snellen chart.
20/20 vision does not mean "perfect vision” it indicates that at a distance of 20 feet, the eye can see what a normally seeing eye should see at that distance
as the bottom number increases, visual acuity decreases (e.g., a person with 20/200 vision must stand at a distance of 20 feet to see what most people can see from 200 feet away)
a person is considered legally blind if her visual acuity is 20/200 or less in the better eye, after the best possible correction with glasses or contacts
field of vision when gazing straight ahead, a normal eye is able to see objects within a range of approximately 180 degrees
one is considered legally blind if he is restricted to an area of 20 degrees or less from the normal 180-degree field
some people have good central vision but poor peripheral vision at the outer ranges of the visual field; others cannot see things clearly in the central visual field but have relatively good peripheral vision
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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2. EDUCATIONAL DEFINITIONS OF VISUAL IMPAIRMENTS
The definition of visual impairments in IDEA emphasizes the relationship between vision and learning: "an impairment in vision that, even with correction, adversely affects a child's educational performance."
Educators classify students with visual impairments based on the extent to which they can use vision and/or tactile means for learning:
totally blind student receives no useful information through the sense of vision and must use tactile and auditory senses for all learning.
functionally blind child has so little vision that she learns primarily through the other senses; however, she may be able to use her limited vision to supplement the information received from auditory and tactile senses and to assist with certain tasks (e.g., moving about the classroom)
low vision child uses vision as a primary means of learning and generally learns to read print
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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4. TYPES AND CAUSES OF VISUAL IMPAIRMENT
refractive errors the size and shape of the eye prevent light rays from focusing clearly on the retina; can usually be corrected by glasses or contact lenses
myopia, or nearsightedness, the eye is larger than normal from front to back; the image conducted to the retina is thus somewhat out of focus; can see near objects clearly, but more distant objects are blurred or are not seen at all
hyperopia, or farsightedness, the eye is shorter than normal, preventing the light rays from converging on the retina; difficulty seeing near objects clearly but able to focus well on more distant objects
astigmatism distorted or blurred vision caused by irregularities in the cornea or other surfaces of the eye; both near and distant objects may be out of focus
Other Causes of Visual Impairment
strabismus an inability to focus on the same object with both eyes because of an inward or outward deviation of one or both eyes
amblyopia reduction in or loss of vision in the weaker eye from lack of use
nystagmus a rapid, involuntary back-and-forth movement of the eyes in a lateral, vertical, or rotary direction; can cause problems in focusing and reading
albinism lack of pigmentation in the eyes, skin, and hair; results in moderate to severe visual impairment by reducing visual acuity and causing nystagmus
deficient color vision difficulty distinguishing certain colors; red-green confusion is most common; usually not an educationally significant visual impairment
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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5. TYPES AND CAUSES OF VISUAL IMPAIRMENT (con’t)
cataract a cloudiness in the lens of the eye that blocks the light necessary for seeing clearly; vision may be blurred, distorted, or incomplete
glaucoma a prevalent disease marked by abnormally high pressure within the eye; central and peripheral vision are impaired--or lost entirely--when the increased pressure damages the optic nerve
diabetic retinopathy individuals with diabetes frequently have impaired vision due to hemorrhages and the growth of new blood vessels near the retina; the leading cause of blindness for people between 20 and 64 years of age
retinitis pigmentosa (RP) a gradual degeneration of the retina; first symptom is usually difficulty in seeing at night, followed by loss of peripheral vision; the most common of all inherited retinal disorders
macular degeneration a fairly common condition in which the central area of the retina gradually deteriorates, causing loss of clear vision in the center of the visual field, making tasks such as reading and writing difficult
retinopathy of prematurity (ROP) an abnormally dense growth of blood vessels and scar tissue in the eyes caused by administering high levels of oxygen to at-risk infants; results in visual impairment and often total blindness; formerly called retrolental fibroplasia
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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6. BRAILLE
Braille a system of reading and writing in which letters, words, numbers, and other systems are made from arrangements of raised dots--is the primary means of literacy for people who are blind.
a complex system that uses abbreviations, called contractions, that help save space and permit faster reading and writing (e.g., if the letter r stands by itself, it means rather; the word myself in braille is written myf)
frequently used words (e.g., the, and) have their own special contractions
math, music, foreign languages, and scientific formulas can be put into braille
the most efficient approach to reading by touch; faster than reading the raised letters of the standard alphabet
most children who are blind are introduced to braille at about the first grade
although not as difficult to learn as it first appears, usually takes several years for children to become thoroughly familiar with the system and its rules
the speed of braille reading varies a great deal from student to student; almost always much slower than the speed of print reading
young children generally learn to write braille using a brailler, a six-keyed device that somewhat resembles a typewriter
older students are usually introduced to the slate and stylus, in which the braille dots are punched out one at a time by hand, from right to left
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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7. LOW VISION AND ITS EFFECTS
Those with congenital low vision view themselves as whole; they do not have remaining or residual vision.
Those with low vision generally view the environment as stationary and clear.
Low vision offers a different aesthetic experience.
20/20 acuity is not needed for visual function for most tasks or for orientation and mobility within most environments.
Clinical measurements do not dictate visual functioning.
Those with low vision can enhance visual functioning through the use of optical aids, nonoptical aids, environmental modifications and/or techniques.
The use of low vision is not in all circumstances the most efficient or the preferred method of functioning.
Low vision has unique psychological aspects.
Those who have low vision may develop a sense of visual beauty, enjoy their visual abilities, and use vision to learn.
[Source: Adapted from A. L. Corn, 1989.]
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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8. VISUAL FUNCTIONING: LEARNING TO SEE
In contrast with earlier “sight-saving” classes, there is great emphasis today on teaching children with low vision to use their vision as effectively as possible.
Natalie Barraga demonstrated that even children with extremely limited vision could improve their visual functioning dramatically
visual efficiency and functional vision are related terms that denote how well a person uses whatever vision he has; includes such skills as controlling eye movements, adapting to the visual environment, paying attention to visual stimuli, and processing visual information rapidly
the fundamental premise is that children learn to see and must be actively involved in using their own vision
Corn (1989) suggests four goals around which to base instructional activities in a program in the use of low vision:
To gain information from directed visual experience.
To gain information from incidental visual experiences.
To gain an appreciation of visual experiences.
To utilize vision for the planning or execution of a task.
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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9. STUDENTS WITH LOW VISION: READING PRINT MATERIALS
Students with low vision use three basic approaches for reading print:
approach magnification (reducing the distance between the eye and the page of print)
lenses (optical devices)
large type
Some disadvantages of large print books and materials:
fewer words can be seen at once
difficult to read smoothly with a natural sweep of eye movements
size and weight of large-print texts make them difficult to handle
may not be readily available after the school years
student may become nonfunctional reader with regular type
In addition to print size, other equally important factors are:
the quality of the printed material
the contrast between print and page
the spacing between lines
the illumination of the setting in which the child reads
It is generally agreed that a child with visual impairments should use the smallest print size that she can read comfortably.
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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10. LISTENING SKILLS
Children with visual impairments must obtain an enormous amount of information by listening.
children with visual impairments do not automatically develop the ability to listen effectively
nor do they necessarily listen better than their normally sighted peers do
systematic development of listening skills is an important component of the education program of virtually every child with visual impairments
listening involves several components, including attention to and awareness of sounds, discrimination, and assignment of meaning to sound
Learning-to-listen activities can take an almost unlimited variety of forms:
discriminating between sounds that are near and far, loud and soft, high-pitched and low-pitched
identifying a new word added to a sentence
listening for important details while there are distracting background noises
differentiating between factual and fictional material
responding to verbal analogy questions
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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11. ORIENTATION AND MOBILITY
orientation the ability to establish one's position in relation to the environment through the use of the remaining senses
mobility the ability to move safely and efficiently from one point to another
Orientation and mobility (O&M) instruction involves many specific techniques for teaching students with visual impairments to understand their environment and maneuver through it effectively. Training should be given by qualified O&M specialist.
The long cane is the most widely used device for adults with severe visual impairments who travel independently.
the traveler does not tap the cane but sweeps it lightly in an arc while walking to gain information about the path ahead
the cane serves as both a bumper by protecting the body from obstacles such as parking meters and doors, and as a probe to detect in advance things such as drop-offs or changes in travel surface
the cane cannot detect overhanging obstacles such as tree branches and provides only fragmentary information about the environment, particularly if the person is in new or unfamiliar surroundings
About 2% of people with visual impairments travel with the aid of a guide dog.
guide dogs do not take a person where he or she wants to go; like the cane traveler, the guide dog user must also have good O&M skills
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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12. SIGHTED GUIDE TECHNIQUE
Most people with visual impairments find it necessary to rely occasionally on the assistance of others. The sighted guide technique is a simple method of helping a person with visual impairment to travel.
When offering assistance to a person who is blind, speak in a normal tone of voice and ask directly, "May I help you?" This helps him locate you.
Do not grab the arm or body of the person who is blind. Permit him or her to take your arm.
The person with visual impairment should lightly grasp the sighted person's arm just above the elbow and walk half a step behind in a natural manner.
The sighted person should walk at a normal pace, describing curbs or other obstacles and hesitating slightly before going up or down. Never pull or push a person who is blind when you are serving as a sighted guide.
Do not try to push a person who is blind into a chair. Simply place his or her hand on the back of the chair, and the person will seat himself.
W. L. Heward, Exceptional Children, 6e,  2000 by Prentice-Hall, Inc. All rights reserved.
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