New Legal Blindness Guidelines Explained
Sunday, September 5, 2010 at 08:05PM
Laura Windsor, O.D. in Achromatopsia, Albinism, Cone Rod Dystrophies, Cone Rod Dystrophy, Diabetic Retinopathy, Diabtic Retinopathy, ETDRS Chart, Head Injury, Histoplasmosis, Legal Blindness, Legally Blind, Macular Degeneration, Retinitis Pigmentosa, Snellen Acuity, Stroke, TBI, Visual Acuities, Visual Field Loss, Visual Impairments

Many people are always curious what it means to be legally blind. A person can be declared legally blind by one of two ways: either their visual acuities are reduced or by a constriction of their peripheral visual fields. To be legally blind, you must have problems and loss in both eyes and it cannot be made better with the use of glasses or contact lenses.

Visual Field Constriction and Legal Blindness

A person can have a restriction of the peripheral visual field of 20 degrees or less in both eyes and be considered legally blind. The most common condition that causes this is retinitis pigmentosa (RP) and in some cases, a stroke or traumatic brain injury.

Visual Acuities and Legal Blindness

A few years ago, the United States Social Security Administration recognized the diversity in newer visual acuity charts and tests done being done by practioners. Some acuity tests only measured at 20/100 and  20/200 levels. Newer charts and low vision charts are able to test in increments between those levels like 20/120 and 20/160. This led to the change in the guidelines.

The Social Security Administration clarified the rules for the determination of legal blindness. They released this statement:

"Most test charts that use Snellen methodology do not have lines that measure visual acuity between 20/100 and 20/200. Newer test charts, such as the Bailey-Lovie or the Early Treatment Diabetic Retinopathy Study (ETDRS), do have lines that measure visual acuity between 20/100 and 20/200."

Therefore if the visual acuity is measured with one of the newer testing charts, and the patient cannot read any of the letters on the 20/100 line, the Social Security Administration will determine that the patient has statutory legal blindness based on a visual acuity of 20/200 or less.

For example: if a patient’s best-corrected distance visual acuity in the better eye was determined to be 20/160 using an ETDRS chart, the SSA will find that the patient has legal blindness. But, if your best-corrected visual acuity for distance in the better eye was determined to be 20/125+1 using an ETDRS chart, the SSA will find that the patient does not have statutory legal blindness as the patient was able to read one letter on the 20/100 line. The +1 at the end of the acuity signifies that they were able to read one letter on the 20/100 line.

The new guidelines specifies that regardless of the type of test chart used, the patient does not have statutory blindness if they can read at least one letter on the 20/100 line in one eye. This new guideline helps many visually impaired patients to qualify for disability that would have normally been denied coverage.

Common conditions that can cause legal blindness are age related macular degeneration, diabetic retinopathy, retinitis pigmetosa, albinism, achromatopsia, Stargardt's disease, cone rod dystrophies, histoplasmosis and many others. For more information about conditions that cause low vision, got to .

Article originally appeared on The Low Vision Blog (
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