Quick answerIn the United States, legal blindness is defined by how well you see, not by a glasses prescription number. You are considered legally blind if your best-corrected visual acuity is 20/200 or worse in your better eye (meaning even with glasses or contacts), or if your visual field is 20 degrees or narrower. A prescription of roughly -2.5 D on its own does not make you legally blind if glasses correct your sight.
Key takeaways
- Legal blindness in the U.S. is based on visual acuity or visual field, not the prescription itself.
- The threshold is 20/200 or worse in your better eye with best correction, or a field of 20 degrees or less.
- Because it is measured with correction, glasses that fix your vision usually mean you are not legally blind.
- A large minus number (like -8.00) is very nearsighted, but if glasses correct it to 20/40, you are not legally blind.
- Only an eye doctor can determine legal blindness; it is a clinical and legal status.
What does legally blind mean?
Legally blind is a threshold used in the United States for benefits and services, not a description of total blindness. It is defined by two measures: central visual acuity of 20/200 or worse in the better eye with best correction, or a visual field of 20 degrees or less. Many people who are legally blind still have some usable vision. The key word is corrected: the measurement is taken with your best glasses or contacts in place.
Is legal blindness a prescription number?
No. This is the most common misconception. A glasses prescription describes how much lens power you need, while legal blindness describes how well you can see after that lens is applied. Two people with the same prescription can have very different corrected vision. So there is no single diopter value, like -5.00 or -8.00, that automatically counts as legally blind.
How 20/200 vision works
Visual acuity like 20/200 compares your vision to normal. It means you must be as close as 20 feet to see what a person with standard vision can see from 200 feet. Normal vision is 20/20. If, even with the strongest helpful correction, your better eye cannot read better than the 20/200 line, that meets the acuity part of the legal-blindness definition.
| Measure | What it means |
|---|---|
| 20/20 | Normal reference vision |
| 20/40 | Often the minimum for a U.S. driver's license (varies by state) |
| 20/200 (best-corrected) | Meets the acuity threshold for legal blindness |
| Visual field 20 degrees or less | Meets the field threshold for legal blindness |
Can glasses correct legal blindness?
If glasses or contacts bring your vision to better than 20/200 in your better eye, you are not legally blind, even with a strong prescription. Legal blindness applies when correction cannot improve your sight past the threshold, which usually involves an eye condition rather than simple refractive error. This is why being very nearsighted is not the same as being legally blind.
When to see an eye doctor
Only an optometrist or ophthalmologist can measure your best-corrected acuity and visual field and determine legal blindness, which can affect eligibility for certain benefits. If your vision cannot be fully corrected with glasses, or you notice a loss of side vision, see an eye-care professional. This article is general education, not medical or legal advice. Understand your own numbers with our Prescription Decoder and how to read them in how to read a glasses prescription.
From our test bench. People often read a big minus number on their prescription and assume it means legal blindness. It does not. What matters is the vision you have with the lens on. We always separate the two: the prescription is the power your glasses supply, and legal blindness is about the sight that remains when the best correction still is not enough.
FAQ
What prescription is considered legally blind?
There is no specific prescription. Legal blindness in the U.S. is defined as best-corrected visual acuity of 20/200 or worse in the better eye, or a visual field of 20 degrees or less, not by a diopter value on your glasses prescription.
Is -2.5 or -8.00 legally blind?
Not by itself. Those numbers describe nearsightedness. If glasses or contacts correct your vision to better than 20/200, you are not legally blind, regardless of how strong the prescription is.
Does legally blind mean you cannot see anything?
No. Many legally blind people have some usable vision. Legal blindness is a threshold for benefits and services, defined by acuity or visual field, not total loss of sight.
Can you drive if you are legally blind?
Generally no. U.S. driving typically requires around 20/40 vision (rules vary by state), which is far better than the 20/200 legal-blindness threshold. An eye doctor and your state's licensing rules determine eligibility.
General education, not medical or legal advice. Related: how often to get an eye exam · Browse eyeglasses · Last updated: August 14, 2026
