National Technical Assistance Center on Blindness and Visual Impairment (NTAC-BVI)

NTAC-BVI
Mississippi State University

What is Blindness and Low Vision?

Often when we think of blindness we think of a person who has no vision at all, but how much can a person see and still be considered blind? Here in the United States we have had a legal definition of blindness in place since about 1935. The definition helps us to understand a level of vision loss that without some kind of intervention or training may result in difficulty or the inability to do certain everyday tasks like reading the newspaper or recognizing a friend.

Legally Blind:

"Central visual acuity 20/200 or less in the better eye with best correction, or widest diameter of visual field subtending an angle of no greater than 20 degrees."

Visual Impairment:

A person whose best corrected vision is between 20/70 to 20/200 is often referred to as "visually impaired" or having "low vision." This person would not be legally blind, but may still have some difficulty in certain visual environments.

Central Vision Loss

So, what is central vision loss? Most of our fine detailed vision is in the center of our visual field, and certain eye conditions like Macular Degeneration or Stargardt’s Disease may interfere with our central vision, making it difficult to read or recognize faces. Here are examples of vision loss with a severe case of macular degeneration:

Photo from the National Eye Institute
Photo from the National Eye Institute

Photo from St. Luke’s Eye Institute
Photo from St. Luke’s Eye Institute

There is damage to the retina that makes it challenging to see in the central part of your vision. A person may need more light to see details, and colors and fine details may be difficult to discern. This includes reading vision. In some cases, the person may have varying degrees of central vision and in the periphery, straight lines may appear wavy like the photo of the man playing golf. Severity of the central vision loss can vary considerably.

Possible accommodations

Accommodations vary depending on the individual and the task they are addressing, so it is always good to ask the person. However, there are a few accommodations that might be useful. A person might need more light, and magnification aids may be very beneficial in helping someone to read both close up and far away. A person with this type of vision loss might also benefit from a magnification program for a workstation computer. It will be very helpful for them to receive materials in an electronic medium so they can enlarge to a size that is useful for them.

Photo from Clarity solutions
Photo from Clarity solutions

Examples of some reading aids
Examples of some reading aids

Tunnel Vision

The definition of legal blindness also includes vision that might allow a person to see in the central part of their vision, but not in the periphery. This would include eye conditions like glaucoma or retinitis pigmentosa. The person might see something like this:

Photo from the National Eye Institute
Photo from the National Eye Institute

Photo from the National Eye Institute
Photo from the National Eye Institute

This type of vision might be considered tunnel vision, and can be very confusing to observers because the person may have 20/20 vision and be able to read small print, or see something across the room, but have difficulty finding a chair or have difficulty locating something outside their frame of vision. This type of vision impacts travel vision more than reading vision. Although these photos make it look as though there are black areas around the vision, that is not what the person sees. They only pick up the visual part, so often they may not be sure if they are missing something.

Possible Accommodations

The person may use a dog guide or a white cane to help them in identifying drops offs or obstacles along their path.

Blind Spots

Some people may have vision that makes it difficult to see because of blind spots and/or poor acuity. This would include eye conditions like diabetic retinopathy. This is how a person might see with diabetic retinopathy.

Normal Vision vs. Vision with Diabetic Retinopathy
Normal Vision vs. Vision with Diabetic Retinopathy

Photo from the National Eye Institute
Photo from the National Eye Institute


Notice everything is a bit blurry and there are places where there are blind spots. These spots may move around as they are often caused by traces of blood in the vitreous fluid in the eye. One confusing thing about this type of vision is that it may vary from day to day. So a person may see well enough to drive one day, and have difficulty seeing the next. As the blood is reabsorbed into the body, vision returns.

Possible Accommodations

A person with permanent or reoccurring blind spots may benefit from magnification, or even using a program that has speech or large print output. They also benefit from getting materials in an electronic medium rather than hard copies. Again, it is always good to just ask the person what their needs might be.

Low Vision

There is considerable variability in the ability of people with partial vision to sue their vision. Some might see some images better than others, depending on factors such as color, glare, movement, fatigue, lighting, and size. For example, a person with partial vision may see someone in a red shirt, and miss someone in a gray shirt, or they may experience temporary eye fatigue that causes them difficulty focusing. They may also avoid bright light or glare because it is uncomfortable or painful to them. Often, they may be considered legally blind. Partial vision, known as low vision, might include someone who has an advanced case of cataracts, retinitis pigmentosa, retinopathy of prematurity, or who experienced some type of eye trauma.

Photo from the National Eye Institute
Photo from the National Eye Institute

Possible Accommodations

A person with low visual acuity may benefit from magnification on a computer monitor, large print materials, or the use of a hand-held magnifier or desktop Electronic Magnification Device. If they need to do large amounts of reading they may prefer audio access, and can obtain access through speech output on a computer or through a digital recording. Depending on how much vision they have, they may use a white cane or guide dog.

Total Blindness

Many people who are considered totally blind may still have light perception or be able to see some movement or bright colors. Others may not have any vision, or may have had their eyes removed. Medically they may be referred to as having light perception only or no light perception. Either way, they are considered to have no useable vision for reading or mobility. Causes can include detached retinas, retinitis pigmentosa, corneal scarring, or glaucoma.

Figure 1: Light perception only
Figure 1: Light perception only

Possible Accommodations

Individuals who are blind may use braille, audio, or tactile means of getting information. There are computer access programs that allow them to access information on a computer, and many use iOS technologies to assist with visual tasks. For example, there are apps that identify money or colors. They make use of their other senses to get around, and usually use a white cane or guide dog for mobility.