page_title: Visual impairment
section_title: Classification
hierarchical_section_title: Visual impairment / Classification
context_page_description: Visual impairment, also known as vision impairment or vision loss, is a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses. Some also include those who have a decreased ability to see because they do not have access to glasses or contact lenses. Visual impairment is often defined as a best corrected visual acuity of worse than either 20/40 or 20/60. The term blindness is used for complete or nearly complete vision loss. Visual impairment may cause difficulties with normal daily activities such as driving, reading, socializing, and walking.
  The most common causes of visual impairment globally are uncorrected refractive errors, cataracts, and glaucoma. Refractive errors include near-sightedness, far-sightedness, presbyopia, and astigmatism. Cataracts are the most common cause of blindness. Other disorders that may cause visual problems include age-related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections. Visual impairment can also be caused by problems in the brain due to stroke, premature birth, or trauma among others. These cases are known as cortical visual impairment.
context_section_description: The definition of visual impairment is reduced vision not corrected by glasses or contact lenses. The World Health Organization uses the following classifications of visual impairment. When the vision in the better eye with best possible glasses correction is:
  20/30 to 20/60 : is considered mild vision loss, or near-normal vision
  20/70 to 20/160 : is considered moderate visual impairment, or moderate low vision
  20/200 to 20/400 : is considered severe visual impairment, or severe low vision
  20/500 to 20/1,000 : is considered profound visual impairment, or profound low vision
  More than 20/1,000 : is considered near-total visual impairment, or near total blindness
  No light perception (NLP) : is considered total visual impairment, or total blindness
  Blindness is defined by the World Health Organization as vision in a person's best eye with best correction of less than 20/500 or a visual field of less than 10 degrees. This definition was set in 1972, and there is ongoing discussion as to whether it should be altered to officially include uncorrected refractive errors.
caption: A typical Snellen chart that is frequently used for visual acuity testing.