Understanding Legal Blindness: Definitions, Criteria, and Types of Vision Loss

In the United States, a person is classified as legally blind when the best‑corrected central visual acuity in the better eye is 20/200 or worse. In practical terms, this means that an object a person with normal vision can read from 200 feet away must be within 20 feet for a legally blind individual, even when wearing glasses or contact lenses.

Blindness refers to a loss of vision that cannot be fully corrected. “Partial blindness” (often called low vision) describes reduced sight, whereas “total blindness” means no perception of light at all.

The legal definition has been in place since the mid‑1930s and is used to determine eligibility for services, accommodations, and benefits.

Official definition: “Central visual acuity of 20/200 or less in the better eye with correcting lenses, or a visual field whose widest diameter does not exceed 20 degrees.”

Thus, even with corrective surgery or lenses, a legally blind person must be within 20 feet to see what a person with typical vision could discern from 200 feet.

Someone whose best‑corrected vision is 20/40 to 20/200 is considered to have low vision or visual impairment. They are not legally blind but may experience difficulty in certain visual environments.

Functional vision loss (FVL), also known as non‑organic vision loss, describes a decrease in acuity or visual field that is not linked to an identifiable ocular lesion. FVL is classified under conversion disorder.

Central Vision Loss

Central vision provides the detail needed for tasks such as reading. Loss of this detailed vision is termed central vision loss.

Conditions that can affect central vision include:

• Age‑related macular degeneration
• Diabetic retinopathy
• Macular hole
• Other macular diseases

Tunnel Vision

Tunnel vision preserves central sight but restricts peripheral awareness, which can hinder navigation and mobility.

Potential causes include:

• Glaucoma
• Retinitis pigmentosa
• Optic nerve damage
• Advanced cataract

Blind Spots

Blind spots are localized areas where vision is absent, often caused by vitreous hemorrhage or retinal lesions. The size and location of these gaps may vary day to day.

Conditions that may produce blind spots include:

• Vitreous hemorrhage
• Retinal detachment
• Macular edema
• Optic neuritis

Partial Vision (Low Vision)

Partial or low vision denotes reduced visual function that differs among individuals, depending on the underlying condition, age, and overall eye health.

Some individuals with low vision meet the legal blindness threshold. Common causes are:

• Glaucoma
• Cataract
• Retinal dystrophies
• Optic neuropathy

Total Blindness

Total blindness means no perception of light whatsoever.

Causes include:

• Severe optic nerve damage
• Advanced retinal degeneration
• Congenital anophthalmia
• Traumatic injury to the eye or visual pathways

While the public often equates blindness with total loss of sight, U.S. legal definitions recognize a spectrum of visual impairment. Anyone who meets the legal criteria—despite corrective measures—may qualify for assistance with daily activities.