What is Visual Impaired?

  

What is Visual Impaired?

Vision impairment refers to when you lose part or all of your ability to see (or vision). The impairment must persist even with the use of eyeglasses, contact lenses, medication, or surgery.

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Many people have some type of visual problem at some point in their lives. Some can no longer see objects far away. Others have problems reading small print things. These types of conditions are often easily treated with eyeglasses or contact lenses. But when one or more parts of the eye or brain that are needed to process images become diseased or damaged, severe or total loss of vision can occur. In these cases, vision can't be fully restored with medical treatment, surgery, or corrective lenses like glasses or contacts. The American Foundation for the Blind estimates that 10 million people in the United States are visually impaired. Visual impairment is a term experts use to describe any kind of vision loss, whether it's someone who cannot see at all or someone who has partial vision loss. Some people are completely blind, but many others have what's called legal blindness. They haven't lost their sight completely but have lost enough vision that they'd have to stand 20 feet from an object to see it as well as someone with perfect vision could from 200 feet away.

Vision Impairment Types

How vision impairments are classified differs across countries. The World Health Organization (the WHO) classifies visual impairment based on two factors: the visual acuity, or the clarity of vision, and the visual fields, which is the area from which you are able to perceive visual information, while your eyes are in a stationary position and you are looking straight at an object.


The Snellen Chart is used to test visual acuity. Your visual acuity is calculated using two numbers. The first number is the distance between the person reading the chart and the chart. The second number is the distance that a person with normal vision would have to stand from an object to see what you did at 20 feet. For example, a visual acuity of 20/80 means that you can read the chart from 20 feet away as well as a person who could read the chart from 80 feet away. In other words, what a person with normal vision would see from 80 feet away, you can't see until you move closer to only 20 feet away. This image shows the crossover between the eyes to create the visual fields.

Three Types of Vision Impairments

The three types of vision impairments are low visual acuity, blindness, and legal blindness (which varies for each country):

• Low visual acuity, also known as moderate visual impairment, is a visual acuity between 20/70 and 20/400 with your best-corrected vision, or a visual field of no more than 20 degrees
• Blindness is a visual acuity of 20/400 or worse with your best-corrected vision or a visual field of no more than 10 degrees
• Legal blindness in the United States is a visual acuity of 20/200 or worse with your best-corrected vision or a visual field of no more than 20 degrees.

Vision Impairment Causes

The causes of vision impairment include:

• Glaucoma
• Cataracts
• Trachoma
• Diabetic retinopathy
• Amblyopia, or the lack of use of an eye in childhood and many others, etc.