Both eye injury and disease can affect vision. The clarity of vision is called visual acuity, which ranges from full vision to no vision. Acuity is usually measured on a scale that compares a person's vision at 20 feet with that of someone who has full acuity. Therefore, a person who has 20/20 vision sees objects at 20 feet with complete clarity, but a person with 20/200 vision sees at 20 feet what a person with full acuity sees at 200 feet.

In the United states, legal blindness is defined as visual acuity worse than 20/200 in the better eye even after correction with eyeglasses or contact lenses.


Several disorders can lead to blindness including:

  • cataract, which is the most common cause and can be cured with surgery
  • infection, which is preventable and is not common in North America
  • diabetes, which is often preventable
  • macular degeneration, which affects central vision and is preventable and treatable in fewer than 10% of people
  • glaucoma which is highly treatable and if treated early should not lead to blindness

The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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