What Is 20/20 Vision?

One of the most commonly asked questions in an eye exam comes right after the refraction, or glasses prescription check: “What is my vision?”

Almost invariably, people know the term “20/20”. In fact, it’s a measure of pride for many people. “My doctor says I have 20/20 vision.” Or, on the other side of that same coin, having vision that is less than 20/20, say 20/400, can be a cause of great concern and anxiety. In this discussion I will describe what these terms actually mean.

To lay the foundation, let’s discuss some common terms. Visual acuity (VA) is clarity or sharpness of vision. Vision can be measured both corrected (with glasses or contact lenses) and uncorrected (without glasses or contact lenses) during the course of an eye exam. The result of an eye exam boils down to two different but related sets of numbers: your VA and your actual glasses prescription.

The notation that doctors use to measure VA is based off of a 20-foot distance. This is where the first 20 in 20/20 comes from. In Europe, since they use the metric system, it is based on meters. The 20/20 equivalent is 6/6 because they use a 6-meter test distance. The second number is the smallest line of letters that a patient can read. In other words, 20/20 vision means that at a 20-foot test distance, the person can read the 20/20 line of letters.

The technical definition of 20/20 is full of scientific jargon - concepts such as minutes of arc, subtended angles, and optotype size. If you’d like to read more of the technical details there is a well-written article with illustrations by Dr. John Ellman, you can find here.  For the purposes of our discussion here I’ll try to explain it in less technical terms.

“Normal” vision is somewhat arbitrarily set as 20/20 (some people can see better than that). Let’s say you have two people: Person A with 20/20 vision and Person B with 20/40 vision. The smallest line of letters that person B can see at 20 feet is the 20/40 line.  Person A, with “normal” 20/20 vision, could stand 40 feet away from that same line and see it. There is somewhat of a linear relationship in that the 20/40 letters are twice the size of the 20/20 letters and someone with normal vision could see a 20/40 letter at twice the distance as the person with 20/40 vision.

So how does this translate to a glasses prescription?

Eye doctors can often estimate what your uncorrected VA will be based on your glasses prescription. This works mainly for near-sightedness. Essentially, every quarter step of increasing glasses prescription (i.e. -1.25 as compared to -1.50) means a person can see one less line on a VA chart.

A prescription of - 1.25 works out to roughly 20/50 vision, -1.50 to 20/60 and so on. Anybody with an anatomically sound eyeball, meaning the absence of any kind of disease process, should generally be correctable to 20/20 with glasses or contact lenses. It is important to note, however, that rarely a person’s best corrected VA may be less than 20/20 with no noticeable signs of disease.

Far-sightedness is more difficult to estimate because it is affected by a number of other factors, including one’s age and focusing ability. But that’s a topic for another article.

So there you have it! Hopefully this has shed some light on what these measurements that we take actually mean, and it has allowed you to understand your eye health a little bit better.

What Is Refraction & Why Doesn't Health Insurance Cover It?

A refraction is a test done by your eye doctor to determine if glasses will make you see better and what your prescription is.

The charges for a refraction are covered by some insurances but not by all.

For example, Medicare does not cover refractions because they consider it part of a “routine” exam and Medicare doesn’t cover most “routine” procedures--only health-related procedures.

So if you have a medical eye problem like cataracts, dry eyes, or glaucoma then Medicare and most other health insurances will cover the medical portion of the eye exam but not the refraction.

Some people have both health insurance--which covers medical eye problems--and vision insurance--which covers “routine” eye care (no medical problems) such as refractions and eyeglasses.

If you come in for a routine exam with no medical eye problems or complaints and you have a vision plan, then the refraction is usually covered by your vision insurance.  But what if you have a known issue (cataracts, dry eyes, diabetes, etc) AND need a refraction?  It depends on the plan(s) of course which greatly vary in the what they permit and approve.  Some health plans work with these vision plans through a process called coordination of benefits to allow both same day, while others do not and either require the patient to pay the non-covered refraction test, or return a second time to address each (the routine and non-routine) issues individually.  

Confused yet? You're not alone, but we must follow the rules the insurance companies make. Bottom line: insurance is (overly) complicated.

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Our doctors and staff are committed to providing thorough care with personal attention. At Eye Doctors of Madison, you will find the compassionate care of a small-town doctors' office with the knowledge of a big-city institution. It is our mission to not only treat each patient uniquely but also like family.

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