Legally Blind in One Eye? Nonsense!

Legally Blind in One Eye?  Nonsense!

by Brian Chou, OD, FAAO, FSLS

  • October 7, 2021

Legal blindness refers to meeting specific criteria for reduced vision.  It is a technical definition which allows a visually impaired person eligibility for specific disability benefits, tax deductions, reduced rates for public transportation, and special assistance from utility companies to name a few social services.  Many lay people talk about legal blindness without realizing it has a strict definition.

Legal Blindness Means with Both Eyes and the Best Vision Correction

In the U.S., legal blindness is defined as the inability to see 20/200 even with both eyes open and the best glasses or contact lenses. Let me repeat, both eyes are open to meet the legal blindness criteria. That is why it is nonsense to say that you are legally blind in one eye. Furthermore, legal blindness is defined as vision with the best glasses or contact lenses. That is why it is also nonsensical to say that you are legally blind without glasses or contact lenses.  Finally, it also makes no sense to say that before having LASIK that you were legally blind.  If someone was legally blind before LASIK, they would necessarily still be legally blind after the procedure.

You Can Still Be 20/20 and Legally Blind?

Yes, you can be legally blind even if you can see the 20/20 letters!  An alternative qualification for legal blindness in the U.S. involves measuring the width of your peripheral vision.  An individual that can see the 20/20 letters is legally blind if the peripheral vision is limited to no more than a 20-degree field of view..

How big is a 20-degree field of view?  Hold your hand at arm’s distance away, with your fingers spread as far apart.  The distance between the tip of your pinky and thumb will approximate a 20-degree field of view.  As you can imagine, a 20-degree field of view is tunnel vision.

Causes of Legal Blindness

What are common causes of legal blindness? Cataracts, macular degeneration, retinal detachment, glaucoma, and diabetic retinopathy top the list. These conditions can impair vision even while wearing the best glasses or contact lenses.

Can Keratoconus Lead to Legal Blindness?

At ReVision Optometry, many of our patients have keratoconus, a condition affecting one in several hundred and usually requires special custom contact lenses to restore vision.  Fortunately, keratoconus by itself does not lead to legal blindness although it can cause substantial vision impairment.

Technological advances in treating keratoconus in the past decade – including corneal cross-linking and scleral contact lenses – can stave off disease progression and significantly restore vision.  However, those with keratoconus can also develop other eye conditions including glaucoma, diabetic retinopathy, and macular degeneration.  These other eye conditions, if left undiagnosed and unattended, may lead to legal blindness.  That is why patients with keratoconus still need routine eye examinations, even if their keratoconus has stabilized.


ReVision Optometry in San Diego is a referral-based practice serving the needs of those with keratoconus and other complex eye conditions requiring medically necessary contact lenses to restore vision.  Request an appointment online or call 619.299.6064.