Anyone with uncorrectable, reduced vision is visually impaired. Uncorrectable means vision that is not further improved by spectacles or contact lenses, it does not mean vision when not wearing glasses.

The World Health Organization uses the following classifications of visual impairment. When the vision in the better eye with the best possible glasses correction is:

• 20/30 to 20/60, this is considered mild vision loss, or near-normal vision.
• 20/70 to 20/160, this is considered moderate visual impairment, or moderate low vision.
• 20/200 or worse, this is considered severe visual impairment, or severe low vision.
• 20/500 to 20/1000, this is considered profound visual impairment or profound low vision.
• Less than 20/1000, this is considered near-total visual impairment or near-total low vision.
• No light perception, this is considered total visual impairment, or total blindness.

There are also levels of visual impairment based on visual field loss (loss of peripheral vision).

In the United States, any person with vision that cannot be corrected to better than 20/200 in the best eye, or who has 20 degrees or less of visual field remaining, is considered legally blind.

Visual impairments take many forms and exist in varying degrees. Visual acuity alone is not a good predictor of a person’s vision problems. Someone with relatively good acuity (20/40) can have difficulty functioning, while someone with worse acuity (20/200) might not have any real problems performing daily activities.