Ever wonder what the term “legally blind” means?

There is much confusion about legal blindness, since most individuals who are legally blind have some functional vision and their eyes may look perfectly fine. Legal blindness ranges from low vision to total blindness.

Determining legal blindness

When describing a person’s vision, most people are familiar with the term, “acuity”, meaning how clear or blurred a person’s vision is compared to others. To be registered as legally blind in Massachusetts, an individual must have vision acuity of 20/200 or less in their better eye with the best possible correction (eyeglasses/contacts).

Let’s compare this to a person with 20/20 vision.

If an individual has 20/20 vision, they can see something at 200 feet clearly. If they have 20/200 vision, they must be only 20 feet away to see the same object as clearly as the individual who is 200 feet away.

The second measurement of legal blindness is a field loss of 10 degrees or less in the better eye. Other visual functions impacting vision loss are: Contrast Sensitivity, how clear or clouded the vision is; Motility, how the eyes move together or not and Cerebral vision, how the brain processes images. All these visual functions impact an individual’s vision impairment differently.

Causes and signs of vision loss

Low vision may be due to different eye diseases and/or health conditions. Some major causes of vision loss are Age Related Macular Degeneration, Diabetes, or Glaucoma (See illustrations below). Vision, once lost, cannot usually be restored so getting regularly eye exams is very important to keeping healthy vision. Most vision loss is gradual, painless and unnoticed until a significant vision loss occurs.

Signs of vision loss may include difficulty recognizing faces, inability to read road signs, and difficulty reading print. Complaints may range from ‘lights seem dimmer” or “it’s never bright enough”. Other signs may involve bumping or tripping over items; spilling or leaving food on the plate. For individuals with limited communication skills, new negative behaviors may indicate a recent vision loss.

Role of vision professionals

When telling an individual the news that they are legally blind, many doctors will say nothing can be done to ‘fix’ the person’s vision. This may be true, but there are also many vision professionals who make it easier for their patients transitioning into the world of vision loss.

In next week’s blog we will discuss resources and services available for someone with vision loss, to make it easier for you or someone you know.

illustration of normal vision

glaucoma simulation

illustration of diabetic retinopathy

simulation of age-related macular degeneration