What is Vision Impairment? - Definition, Causes & Symptoms

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  • 0:04 What Is Vision Impairment?
  • 0:17 Vision Impairment Types
  • 1:52 Vision Impairment Causes
  • 2:27 Impairment Signs
  • 3:15 Lesson Summary
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Lesson Transcript
Instructor: Yolanda Williams

Yolanda has taught college Psychology and Ethics, and has a doctorate of philosophy in counselor education and supervision.

Did you know that there are 285 million people in the world living with a vision impairment? Learn about vision impairments, what causes them, and more.

What Is Vision Impairment

A 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.

Vision Impairment Types

The way in which 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 in order to create the visual fields.

Visual Fields Chart

Three Types of Vision Impairments

The 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
  • Eye injuries, such as accidentally being poked in the eye at work
  • Inherited conditions, such as retinitis pigmentosa
  • Infections such as German measles and chlamydia that can be transmitted from the mother to a fetus during pregnancy
  • Age-related macular degeneration
  • Retinal detachment
  • Viral infections of the eyes as a result of Autoimmune Deficiency Syndrome, and/or
  • Retinoblastoma and other eye cancers

Impairment Signs

Children with vision impairments might:

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