Visual Sensory Impairments - Definitions, Prevalence, Etiology

Visual impairment- Genetic term; it ranges from people reading this text who have very mild visual impairment, to those with low vision, and includes those who are totally blind.

Low vision- a person’s corrected vision is lower than normal.

Blindness- an individual has no sight or so little that learning takes place through other senses.

Visual activity- the measure of the smallest image that is distinguishable by the eye.

Visual field- the entire area that can be seen when staring straight ahead, reported in degrees.
        

        Visual impairment is primarily an adult disability, about one-tenth as prevalent in children as in adults. In the general public, rates are 2.6 percent. People with low vision far outnumber totally or functionally blind people, with only 10 to 15 percent of the entire population of persons with visual impairments being totally blind. Although visual impairment is a low-incidence occurrence in the Western World, it is of particularly high prevalence in Third World countries where conditions such as water-borne blindness, vitamin A deficiency and lack of sanitation allow visual impairments to thrive.

        In children, blindness is the least prevalent of all disabilities. 1 in every 10,000 Canadian babies is diagnosed with legal blindness, and 1 in every 1000 children under the age of 18 has severe visual impairments. The majority of children with visual impairments attend general classrooms. Teachers must be aware of this issue and make the required adaptations and accommodations that will assist the students. Among the school aged population, students with low vision comprise between 75 and 80 percent of those who are visually impaired. Some children may be able to read by seeing clearly through one small area, but then have trouble getting around from place to place. Others may be able to see the entire work area, but have difficulty reading it.

        Many people have minor visual losses caused by one of the four common refractive errors: Myopia (being unable to focus images precisely), Hyperopia (too short an eye/too flat a corneal surface), Astigmatism (irregularity in curvature of the cornea) and Presbyopia (eye loses the ability to accommodate near objects). Eye pathologies, such as cataracts, glaucoma, retinoblastoma and retinal detachments, are most common in adults and are the result of damage or disease to one or more eye structures. There are a number of syndromes that are associated with visual impairments; Usher’s Syndrome stresses the link between visual and auditory impairments, and is the leading cause of deaf-blindness. Joubert Syndrome is a rare neurological disorder where individuals show ataxia, slow motor activity, and often abnormal eye movements. Leger Congenital Amaurosis is an inherited retinal degenerative disease.

A Few Facts on Visual Impairments:

-Worldwide, 285 million people are visually impaired due to various causes. 39 million of them are totally blind.

-221 million people are visually impaired because of in corrected refractive errors. Almost all of them could have normal vision restored with eye classes, contacts, or refracted surgery.

-90% of people who are visually impaired live in low and middle income countries.

-51% of all blindness is due to age-related cataracts.

Winser, M. (2008). Children with Exceptionalities in Canadian Classrooms (8th ed.).
Toronto, Canada: Pearson Prentice Hall, pp. 359 – 389.