Visual Disabilities

Learners with Blindness or Low Vision

• Overview- Visual impairments seem to evoke more awkwardness than most other disabilities.

• One reason is that blindness is visible, whereas we often do not realize that a person has impaired hearing

• Blindness is the least prevalent of all disabilities, at least in children

Definition and Classification

• Legal Definition- legally blind- A person who has visual acuity of 20/200 or less in the better eye even with correction or has a field of vision so narrow that its widest diameter subtends an angular distance no greater than 20 degrees.

• Low vision- Visual impairments are not so severe that they are unable to read print of any kind

• Educational Definition- (low vision)- someone who has difficulty accomplishing visual tasks, even with corrective lenses, but who can enhance his or her ability to accomplish these tasks with the use of compensatory visual strategies

Prevalence

• Blindness is primarily an adult disability

• Blindness is approximately one-tenth as prevalent in school-age children as in adults

• About .05 percent of the population ranging from 6 to 17 years of age is classified by the federal government as “visually impaired”

Anatomy and Physiology of the Eye

• Cornea- A transparent cover in front of the iris and pupil in the eye; responsible for most of the refraction of light rays in focusing on an object

• Aqueous humor- A watery substance between the cornea and lens of the eye

• Pupil- The contractile opening in the middle of the iris of the eye

• Iris- The colored portion of the eye; contracts or expands, depending on the amount of light striking it

Anatomy of the Eye cont.

• Lens- A structure that refines and changes the focus of the light rays passing through the eye

• Vitreous humor- A transparent, gelatinous substance that fills the eyeball between the retina and the lens of the eye

• Retina- The back portion of the eye, containing nerve fibers connected to the optic nerve

• Optic nerve- The nerve at the back of the eye, which sends visual information back to the brain

Anatomy of the eye

Measurement of Visual Ability

• Snellen Chart- Used in determining visual acuity; each row corresponds to the distance at which a normally sighted person can discriminate the letters

• Visual efficiency- How well one uses his or her vision, such as control of eye movements, attention to visual detail, and discrimination of figure from background

• Functional visual assessment- An appraisal of an individual’s use of vision in everyday situations

Causes• Refraction- The bending of light rays as they

pass through the structures of the eye• Myopia- Nearsightedness• Hyperopia- Farsightedness• Astigmatism- Blurred vision caused by an

irregular cornea or lens• Glaucoma- A condition of excessive pressure in

the eyeball; cause is unknown; if untreated, blindness results

• Cataracts- Condition caused by clouding of the lenses of the eye; affects color vision and distance

Causes• Diabetic retinopathy- condition resulting from

interference with the blood supply to the retina• Retinitis pigmentosa- degeneration of the

retina; causes the field of vision to narrow and affects night vision

• Tunnel vision- problems in peripheral vision• Night blindness- problems in seeing at low

levels of illumination• Cortical visual impairment- childhood condition

that is characterized by large day-to-day variations in visual ability

Causes

• Retinopathy of prematurity (ROP)- Abnormal growth of blood vessels in the eye; related to premature birth

• Strabismus- Eyes are directed inward or outward; cross eyes

• Nystagmus- Rapid involuntary movements of the eyes; can indicate a brain malfunction or inner ear problems

Psychological and Behavioral Characteristics

• Language Development- the lack of vision does not have a very significant effect on the ability to understand and use language

• Intellectual Ability- there is no reason to believe that blindness results in lower intelligence

Psychological & Behavioral Characteristics Cont.

• Orientation and Mobility skills- the ability to have a sense of where one is in relation to other people and objects in order to move in the environment

• Cognitive mapping- allows for better mobility• Academic achievement- direct comparisons of

the academic achievement of students who are blind with that of sighted students must be interpreted cautiously because the groups must be tested under different conditions

Psychological and Behavioral Characteristics

• Social adjustment- social difficulties which may arise are more likely due to society’s inappropriate reaction to blindness

• Social skills may be difficult for people with visual impairments such as smiling; smiling is not as spontaneous a social response as it is for those who are sighted

Psychological and Behavioral Characteristics

• Stereotypic behaviors- Any variety of repetitive behaviors that are sometimes found in individuals who are blind, severely retarded, or psychotic; also called blindisms

Educational Considerations

• Braille– http://www.afb.org/braillebug/

• Use of Remaining Sight

• Listening skills

• Orientation and Mobility (O & M) Training

• Technological Aids

Educational Placement Models• Intinerant teacher services- services for

students who are visually impaired in which the special education teacher visits several different schools to work with students and their general education teachers

• Residential placement- 7 percent of students with low vision loss between the ages of 6 and 21 are placed in a residential institution, wheras only about .5 percent of students with mental retardation are so placed

Early Intervention

• Many infants who are blind lag behind their peers in motor development

• O & M training should be a critical component of preschool programming

• Many advocate that they should be placed in inclusive settings with sighted children; it is critical that teachers facilitate interactions between the children

• Extremely important for parents to be involved

Transition to Adulthood

• Many independent living skills need to be taught explicitly to those who are visually impaired

• Many working-age adults with visual impairments are unemployed, and those who do work are often overqualified for the jobs they hold

• The employment rate for adults aged 21 to 64 who have severe visual limitations was only 26%