What is blindness?

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Legal blindness

In the United States, people are legally blind if their best eye has 20/200 vision or less with the help of glasses or contact lenses. Having 20/200 vision means that a person cannot be more than 20 ft (6.1 m) away to see what a person with normal vision can see from 200 ft (60.96 m) away.

The United States also considers people legally blind if their visual field is 20 degrees or less, even with the help of glasses or contact lenses. Having a visual field of 20 degrees means that people have trouble seeing to the side (peripheral vision) when looking straight ahead. A vision test is used to measure a person's visual field.

Legal blindness does not mean that a person cannot see at all. People who are legally blind often have some vision, but their field of vision may be very narrow or blurry. Or they may have blind spots that glasses cannot correct.

Being diagnosed as legally blind restricts a person's ability to obtain a driver's license. But a legally blind person is usually eligible for low visibility aids and other benefits to help improve daily functioning.

How can you help prevent blindness from diabetes?

This table shows the major causes of blindness in people who have diabetes and what you can do to help prevent vision loss.

Keeping your blood sugar levels and blood pressure within a target range is always important. You also need regular dilated eye exams to help find eye diseases early. Finding and treating eye diseases early can help prevent or delay vision loss.

Major causes of blindness associated with diabetes


How it causes vision loss

How to help prevent it

Diabetic retinopathy

It damages the retina, the section of your eye that captures visual information.

  • Keep blood sugar levels in a target range.
  • Control blood pressure.
  • Get regular eye exams.
  • Treat retinopathy early to keep the disease from progressing.


It increases pressure in the eye, which damages your retina.

  • Get regular eye exams to check for the disease.


It clouds the lens, the section of your eye that focuses light.

  • Protect your eyes from ionizing radiation (X-rays) and UV radiation (sunlight).
  • Keep blood sugar levels in a target range.

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The content above contains general health information provided by Healthwise, Incorporated, and reviewed by its medical experts. This content should not replace the advice of your healthcare provider. Not all treatments or services described are offered as services by us. For recommended treatments, please consult your healthcare provider.