Visual Impairments

Visual impairment is the consequence of a functional loss of vision, rather than the eye disorder itself. Eye disorders which can lead to visual impairments can include retinal degeneration, albinism, cataracts, glaucoma, muscular problems that result in visual disturbances, corneal disorders, diabetic retinopathy, congenital disorders, and infection.

The terms partially sighted, low vision, legally blind, and totally blind are used in the educational context to describe students with visual impairments. They are defined as follows:

Partially sighted - indicates some type of visual problem has resulted in a need for special education
Low vision - generally refers to a severe visual impairment, not necessarily limited to distance vision. Low vision applies to all individuals with sight who are unable to read the newspaper at a normal viewing distance, even with the aid of eyeglasses or contact lenses. They use a combination of vision and other senses to learn, although they may require adaptations in lighting or the size of print, and, sometimes, braille
Legally blind - indicates that a person has less than 20/200 vision in the better eye or a very limited field of vision (20 degrees at its widest point) and
Totally blind students learn via braille or other non-visual media.

There is a wide range of visual impairments. People may be able to discern light, colors, or shapes. Some may be able to read by seeing clearly through one small area but have trouble getting around. Others may be able to see a whole area but have difficulty reading. Some have diseases which cause their visual acuity to fluctuate. The definition of visual impairment used in school settings considers the extent to which a student's vision affects learning and makes special methods or materials necessary.

The rate at which visual impairments occur in individuals under the age of 18 is 12.2 per 1,000. Severe visual impairments (legally or totally blind) occur at a rate of .06 per 1,000.

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Assessments

Characteristics

The effect of visual problems on a child's development depends on the severity, type of loss, age at which the condition appears, and overall functioning level of the child. Many children who have multiple disabilities may also have visual impairments resulting in motor, cognitive, and/or social developmental delays.

A young child with visual impairments has little reason to explore interesting objects in the environment and, thus, may miss opportunities to have experiences and to learn. This lack of exploration may continue until learning becomes motivating or until intervention begins.

Because the child cannot see parents or peers, he or she may be unable to imitate social behavior or understand nonverbal cues. Visual handicaps can create obstacles to a growing child's independence.

Symptoms

The following are common symptoms of visual impairment:

blurry vision
double vision, or seeing two of everything. This occurs when the images that are coming from each eye do not line up properly.
difficulty focusing on either near or far objects
cloudy vision, often described as "looking through a dirty windshield"
seeing so-called floaters or black specks across the field of vision
inability to see certain colors
inability to see peripheral objects, meaning those objects that are to the side, up or down
loss of depth perception
ability only to distinguish light from dark
total loss or absence of all vision

Causes

A person may be born with visual impairments, or they may occur later in life. Common causes of visual impairment include the following:

damage to the visual nerves, such as that caused by head injury, brain tumor, or infection
diabetes
glaucoma, or abnormally high pressure inside the eye
injuries to the eye, such as corneal injuries
brain damage, such as that from a stroke, or brain attack
refractive errors, which means that objects appear blurry only when they are up close or when they are far away. This is commonly known as being nearsighted or farsighted. Nearsightedness, or myopia, means that objects that are far away are not seen clearly. Farsightedness, or hyperopia, means that objects that are close are blurry, while objects far away can be seen clearly. These conditions often are the reasons people need glasses.
color blindness, an inherited condition that is much more likely in males
macular degeneration, a common cause of poor sight in the elderly. This condition affects the retina, or back of the eye, and occurs for unknown reasons.
cataracts, another common cause of poor vision in the elderly, although it can occur even in newborn babies. Cataracts describe a clouding of the lens, or focusing, part of the eye. A congenital cataract is an opacity (cloudiness) in the lens of the eye that is present at, or develops shortly after, birth. The human lens is located behind the pupil and has an important function. It focuses rays of light into the retina to allow image formation. As the lens is able to change is shape, it can focus objects at different distances. Its cells are arranged so that it is transparent, like glass or water. When this arrangement is disturbed in any way, the transparency is lost and an opacity results. This results in blurring and blocking of the retinal image.
aging, which can cause people to need reading glasses or bifocals starting around the age of 40 or 50. This condition is called presbyopia and is considered normal.
astigmatism, or blurred vision in only certain areas of sight, which is caused by abnormal bending of light through the eye
medication side effects, such as those from the heart medication digoxin or the antibiotic ethambutol.
Vitamin A Deficiency (Xerophthalmia) - a recent analysis of data indicates that vitamin A deficiency is the leading cause of childhood blindness. It was estimated that 70% of the 500,000 children who become blind annually do so because of xerophthalmia. This corresponds to a prevalence of roughly 1 million in view of the high mortality among affected children.
Strabismic amblyopia occurs when a strabismus is present and the eyes are not aligned. The brain favors one eye over the other and the non-preferred eye is not adequately stimulated and the visual brain cells do not mature normally.