Low vision is a subspecialty within the professions of optometry and ophthalmology and opticianry dealing with individuals who have less than normal vision even with the most accurate conventional prescription available. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the latter age-related macular degeneration.

Classifying low vision

Anyone with noncorrectable reduced vision is considered to be visually impaired, and can have a wide range of causes. 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

Legal blindness

• 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
• less than 20/1,000 : is considered near-total visual impairment, or near total blindness
• No Light Perception : is considered total visual impairment, or total blindness

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

Go to visual acuity to consult an international visual acuity expression chart.

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 (diameter) or less of visual field remaining, is considered to be "legally blind" or eligible for disability classification and possible inclusion in certain government sponsored programs.