Defining Visual Acuity

The World Health Organization (WHO) defines visual acuity as the capacity of the eye to see fine detail using very clinical measurements as outlined below. These are important measurements as they provide comparisons of what most people can see at a prescribed distance.

An individual who has 20/20 vision is said to have optimal vision as they can see what most people can see at a distance of 20 feet. In comparison, if someone has 20/50 vision that person cannot see an object that is 50 feet away. They could only see the object if they were 20 feet away. In clinical terms the person’s visual acuity would be less than optimal 20/20 vision.

There are also other parameters that help to define vision including what is referred to as your field of vision.

Field of vision is defined as the entire area that a person can see when their eyes are fixed in one position. Simply put, if a person is able to see out of the side of their eye, as well as the front of the eye, they would have a “normal” field of vision. However, if someone is only able to see out of the front of their eye or can only see out of the side of their eye then their field of vision is compromised.

There are two separate conditions that are used to define legal blindness. The first deals with a person’s visual acuity. If you are legally blind your vision (with correction such as glasses or contacts) is 20/200 or less in your better eye. That means if an object is 200 feet away, you have to stand 20 feet from it in order to see it. But a person with normal vision can stand 200 feet away and see that object clearly.

The next way in which legal blindness is defined deals with your field of vision. If your field of vision (what you can only see out of part of your eye such as the front or side of your eye) is less than 20 degrees even if your overall acuity is better than 20/200, that individual would also be considered legally blind.
(WebMD)

Another element that impacts greatly on someone’s vision is lighting. In some instances, brighter lighting may significantly improve an individual’s ability to focus while more limited lighting may be what another person needs to maximize their visual acuity.

A person may also wear glasses or contacts which increases their visual acuity. In this case, a person whose vision without glasses is 20/70 but with correction is 20/20, then that person does not have low vision, as long as they are wearing glasses.

When someone’s vision is 20/70 or less with correction, this is where low vision begins. While they are by no means legally blind, at this level a person may begin to have trouble performing tasks that were never visually challenging in the past. This might include such things as reading standard text such as in a newspaper or performing household chores such as setting the temperature on an oven or identifying controls on a microwave.

People don’t realize that vision can change about every decade. It is commonplace to hear that an older friend or family member has begun to develop cataracts which is causing them to struggle with basic tasks usually because the cataract is blurring vision. At the time of diagnosis – a cataract is beginning to form – there is often a waiting period which can be several months before surgery can be scheduled. Prior to surgery many people do not realize there are simple things they can do to enhance their visual ability while waiting for surgery to happen.

There are many medical diagnoses that affect a person’s vision and anyone experiencing a change in vision should consult an eye professional such as an ophthalmologist. This is a medical doctor specializing in the diagnosis and treatment (including surgery) of eye diseases, and therefore is able to provide ultimate eye care. (An ophthalmologist's expertise is beyond that of an optometrist). While the ophthalmologist is essential to diagnosing various diseases of the eye, they are not generally attuned to knowing what strategies may be used to enhance a person’s ability to perform simple tasks that help to maintain independence.

Serpe Solutions, Inc., does not dispense medical advice. The intent of this company is to provide individuals with strategies and emotional support often accompanying either a temporary or permanent loss of vision.

If you or someone you care about is struggling with the effects of vision loss talk to someone who is living this experience. Contact Amy at 847-372-2523 or amy@serpesolutions.com for assistance. There is no charge for your initial conversation.

Definitions for Vision Impairment

Provided by WHO

World Health Organization

Best Corrected Vision with Glasses/Contacts

20/20 – optimal vision.
20/30 to 20/60 – mild vision loss, or near-normal vision.
20/70 to 20/160 – moderate
visual impairment, or moderate low vision.
20/200 to 20/400 – severe
visual impairment, or severe low vision. In the US, vision of 20/200 in the BETTER eye (with correction) is considered legally blind.
20/500 to 20/1,000 is
considered profound visual impairment, or profound low vision.
Less than 20/1,000 is
considered near-total visual impairment, or near total blindness.
No light perception is considered total visual impairment, or total blindness.