Vision Loss

Key Terms for Understanding Vision Loss


In discussions about understanding vision loss, you’ll commonly hear phrases like visually impaired, low vision, or legally blind. I make reference to each of these terms a lot in my posts and social media. I even have it in my Instagram bio. But what do they actually mean, and and how is it determined what category those with vision loss may fall under?

Key Terms for Understanding Vision Loss

Young woman wearing glasses looking looking intently at phone screen as she holds it near her face. Written on bottom of image in blue lettering: Understanding Vision Loss; Common Terms and Definitions

Visual Acuity

Visual Acuity measures the clarity of your best corrected vision.  This value is determined when your doctor checks your vision using a Snellen eye chart.  A person with perfect vision has 20/20 vision, meaning they can see clearly at 20 feet what should normally be seen at that distance.  Someone with a visual acuity of 20/100 must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

Snellen Eye Chart used for testing visual acuity

The key phrase here is Best Corrected Vision. This means the smallest line you can read on an eye chart while wearing prescribed corrective lenses.  For many retinal diseases such as macular degeneration, retinitis pigmentosa, and Stagardt’s, the damage to the interior of the eye becomes significant enough that glasses/contacts/surgeries are no longer able to correct a portion or all of what that person sees.

Visually Impaired

Many people use visually impaired and low vision interchangeably, but I see them as slightly different classifications. Visual impairment can describe a wide range of visual function, from low vision through total blindness.  Moderate visual impairment occurs when an individual’s best corrected vision is 20/70 to 20/160, whereas severe visual impairment is a visual acuity that exceeds 20/200.  A visually impaired person may also have a range of other impacts to their vision, such as contrast sensitivity, light sensitivity, and difficulty adapting from light to dark spaces.

Low Vision

Magnifier held over open book to assist with understanding vision loss

A person with low vision has uncorrectable vision loss that interferes with daily activities, such as recognizing faces, cooking, reading, and driving, while retaining some usable vision.  Someone with low vision may have a blank spot in the center of their vision, but still see clearly using their peripheral vision, or vice versa.   It is a moderate form of visual impairment, as described above as having a best corrected visual acuity ranging between 20/70 and 20/200.  Many people who are classified as having low vision will undergo a “functional eye exam” at their doctor’s office. This helps determine the range of vision a person has and identifies which types of visual aides may be of the most use for them.

Legally Blind

As with the term visually impaired, legally blind isn’t a functional definition that tells you very much about what a person can see, but rather a classification system. It is used by government entities to determine eligibility for everything from vocational training, disability benefits, low vision devices, and tax exemption programs. A person is considered to be legally blind when their best corrected vision in their better eye exceeds a visual acuity of 20/200 or a visual field of 20 degrees or less.

In their article, What Does “Legally Blind” Mean?, All About Vision offers two interactive tools which show a progressive decline of visual acuity and visual field.

Where Do I Fit In?

Before I started reading more about understanding vision loss, I knew how legally blind was defined, but I wasn’t as clear about visually impaired vs. low vision.  I tend to shy away from classifying myself under any of these terms because even though myopic macular degeneration impacts how well I am able to see, I am still able to perform most functions normally.  If I am asked directly, I would say that I identify as a visually impaired person. I’ve chosen to go with the more broad label, as my visual ability can at times can fluctuate. I also enjoy the opportunity it gives me to dispel misconceptions have about visually impaired people and how although it’s a way to describe me, it’s not the most notable thing about me.

I hope this post clarifies what these different terms mean when you see them used in my posts, and helps you in understanding vision loss a little more!

Theresa is a Maryland native who is grateful to only be a 2-hour flight from Walt Disney World. She loves exploring new locations & cuisines, and can beat anybody in a game of “Oh! You know what else that actor was in?” Although myopic macular degeneration is deteriorating her eyesight, it hasn’t dampened her spirit or sense of humor; she likes to tell people this simply makes her a “temporary visionary.” Visit About Theresa to learn more or send an email to!

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