A person's vision impairment means that their eyesight cannot be corrected to a "normal" level. A loss of visual acuity, in which the eye does not see objects as clearly as usual, and can cause vision impairment. It could also be caused by a loss of visual field, in which the eye can't see as far as it used to without moving the eyes or turning the head.
There are various ways to describe the severity of a person's vision loss. "Low vision" is defined by the World Health Organization as visual acuity between 20/70 and 20/400 with the best possible correction, or a visual field of 20 degrees or less. Blindness is defined as having a visual acuity of less than 20/400 with the best possible correction, or having a visual field of less than 10 degrees.
The severity of vision impairment may be classified differently. In the United States, for example, the term "legal blindness" denotes a person's eligibility for certain educational or federal programs. Legal blindness is defined as having a visual acuity of 20/200 or less with the best possible correction, or having a visual field of 20 degrees or less.
Visual acuity alone cannot predict how much vision loss will affect a person's life. It is also necessary to evaluate how well a person uses their vision. Two people may have the same visual acuity, but one may be better at using his or her vision to perform daily tasks.
Most "blind" people have some usable vision that allows them to move around their environment and do things in their daily lives. A person's functional vision can be assessed by observing them in various settings and observing how they use their vision.
A child's understanding and functioning in the world is altered by vision impairment. Impaired vision can have an impact on a child's cognitive, emotional, neurological, and physical development by potentially limiting the range of experiences and information to which a child is exposed.
Almost two-thirds of children with vision impairment have one or more additional developmental disabilities, such as mental retardation, cerebral palsy, hearing loss, or epilepsy. Children with severe vision impairment are more likely than children with milder vision impairment to have additional disabilities.
People rarely lose their vision during their adolescence. When they do, it is usually due to an injury, such as being hit in the eye or head with a baseball or being involved in an automobile or motorcycle accident.
Some babies are born with congenital blindness, which means they are visually impaired. Congenital blindness can be caused by a variety of factors, including inheritance or infection (such as German measles) transmitted from the mother to the developing fetus during pregnancy. Following birth, the following conditions may cause vision loss:
Amblyopia is a loss of vision in one eye caused by a lack of use of that eye during childhood.Some conditions cause the eyes of a child to send different messages to the brain (for example, one eye might focus better than the other). The brain may then turn off or suppress images from the weaker eye, and vision in that eye may cease to develop normally. This is also referred to as a "lazy eye." Strabismus (crossed or misaligned eyes) is a common cause of amblyopia because the brain begins to ignore messages sent by one of the misaligned eyes.
Glaucoma is characterized by an increase in intraocular pressure. The increased pressure damages the optic nerve, impairing vision. Glaucoma is most commonly seen in older adults, though babies can be born with it and children and teenagers can develop it as well.
Cataracts are cloudy areas in the lens of the eye that can affect one or both eyes. The lens is crystal clear in people who do not have cataracts, allowing light to pass through and focus on the retina. Cataracts prevent light from passing easily through the lens, resulting in vision loss. Cataracts usually form slowly and affect people in their 60s and 70s, but babies can be born with congenital cataracts. Symptoms include double vision, cloudy or blurry vision, difficulty seeing in dim lighting, and faded colors.
Diabetic Retinopathy occurs when the tiny blood vessels in the retina are damaged as a result of diabetes. People with retinopathy may not have any vision problems at first. However, if the condition worsens, they may go blind. Diabetes teens should have regular eye exams because there are no early warning signs for this condition. Diabetes patients should also avoid smoking, keep their blood pressure under control, and maintain an even blood sugar level to help prevent retinopathy.
Macular Degeneration is the gradual deterioration of the macula, the most sensitive region of the retina.The condition causes progressive central vision loss (the ability to see fine details directly in front). Macular degeneration is typically associated with old age (it affects people over the age of 60), but it can occur in younger people as well. Excessive sun exposure and smoking can both increase the risk of age-related macular degeneration. Symptoms may include difficulty reading or watching television, as well as distorted vision in which straight lines appear wavy and objects appear larger or smaller than normal.
Retinitis Pigmentosa is a rare, inherited degenerative eye disease that results in severe vision loss. Symptoms frequently appear in childhood. They include blurred vision at night or in low light, as well as loss of peripheral vision (tunnel vision). While there is no cure for retinitis pigmentosa, medications can help treat its complications.
Trachoma occurs when a highly contagious microorganism known as Chlamydia trachomatis causes inflammation in the eye. It is commonly found in poor rural countries with overcrowding and limited access to water and sanitation. Trachoma-related blindness has all but disappeared in the United States.
If you or your family suspect that you have a visual problem, you will most likely consult an ophthalmologist a medical doctor who specializes in examining, diagnosing, and treating eyes and eye diseases. When someone visits an ophthalmologist, the ophthalmologist will examine the structure of that person's eye. An ophthalmologist may also perform the following simple tests:
Visual Acuity Exam: A person examines an eye chart to determine how well he or she sees at different distances.
Visual Field Exam: This test is used by ophthalmologists to assess side vision, also known as peripheral vision.
Tonometry Exam: This test measures the fluid pressure inside the eye to detect glaucoma.
Many treatments are available if your doctor determines that you have an eye condition that is likely to cause visual impairment. Options may include glasses, contact lenses, eye drops, and other medications. Surgery may be required in some cases. Cataracts, for example, are frequently treated by removing the clouded lens and replacing it with an intraocular lens (an artificial plastic lens that requires no special care and restores vision).
People with visual impairment, like you, do not think about their condition every day, just as you do not think about your eye color every day. However, someone with vision problems may become more easily isolated from others. If a visually impaired person asks for help, don't be afraid to offer it. However, someone who uses echolocation, a cane or a guide dog is likely self-sufficient and may not require assistance.
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