What does 20/20 Vision Mean?

20/20 Vision

What does 20/20 Vision Mean?

In popular culture, we use the phrase ‘20/20 vision’ to mean that we have perfect eyesight, or as a metaphor to mean that we have a clear view of a situation. But while visual acuity literally means seeing clearly, there are few optical and neural factors that lead to 20/20 vision such as:

  • The sharpness of the retinal focus
  • The health and function of the retina
  • The brain’s interpretative ability

The History of 20/20 Vision

When glasses were first invented, the corrective lenses were mostly available as just a “one size fits all” option; reading glasses with convex lenses for close up vision, and concave lenses for seeing into the distance. The ability to correct vision was rudimentary and inexact, because no one had devised a way to measure visual acuity accurately. Various doctors had different eye charts and their own methods of eye testing, but there wasn’t a standardized version, and so the studies and results of eye tests were often inaccurate.

But that changed in 1862, when Dr. Herman Snellen, a Dutch eye doctor, created the Snellen chart.

The original chart used a combination of letters and numbers, but in 1959, the chart was changed to use 10 letters in a font that was specially created to represent an acuity test called The Landolt Broken Rings. The font created by Dr. Louise Sloan, and was designated as the US Standard for acuity testing by the National Academy of Sciences, National Research Council, Committee on Vision in 1980. The broken rings helped measure the minimum perceivable angle of the gap, which improves how we measure visual acuity.

The combination of the two charts is the same chart that is seen today in Kelowna optometry clinics, and it’s commonly known as the big E chart.

How the E Chart Works

The Snellen chart was developed to exact measurements, which became the standardized version. Each line is 25 percent smaller than the line above it, but, as everyone who wears glasses will know, the distance a person stands from the chart is just as important as the measurements of the letters on the chart.

It was determined that to measure the visual acuity, a distance of 20 feet would be the standardized measure used, and a person should be able to see the same detail as a person who doesn’t need glasses at a distance of 20 feet.

When you are reading the E chart, your optometrist may mention numbers like 20/40 or 20/10. The first ‘20’ in 20/20 vision refers to the visual range (in feet) of a person with normal vision; the second number refers to your eyesight range in feet.

The decreasing size of the letters on the chart measures the visual level ranges from 20/200 to 20/10. There are 11 rows of letters on the E chart. The first line with the big E is labeled 20/200; the next line is labeled 20/100 and so on down to the eighth line, which is labeled 20/20. If you can read beyond that line without needing glasses, congratulations, you have better than 20/20 vision.

Advances in Eye Testing

Of course, as eye doctors technology and knowledge of how the eye works became more sophisticated, we began to realize that even though the standard E chart testing we use today is the primary measurement of visual acuity, it doesn’t include other important measurements of sight such as depth perception, night vision, peripheral vision or colour blindness.

Today, our expectation of having 20/20 vision goes a lot further than it did in the 1800s.

A full eye exam has come a long way from merely reading the E chart. Today, we don’t merely check eyes for farsightedness or nearsightedness, we also check for cataracts, glaucoma, and any other abnormalities that may indicate deteriorating vision, which could be due to illness, injury, or aging.

Kelowna Eye exams today also measure how well you can see objects that are similar in brightness compared to their background to measure how well your eyes can see contrast, and how well your eyes can see moving objects. As you can imagine, these eye tests are vitally important for sports, driving, and working in a potentially dangerous environment.

Better than 20/20 Vision

We all aspire to having 20/20 vision, but how possible is it to have better than 20/20 vision?
It is quite possible and quite common; in fact, many young people with healthy eyes can read beyond the 20/20 line on the chart. However, it is normal to lose visual acuity as you age, and the range and type of visual acuity you have at any moment can vary depending on a variety of conditions, including weather, activity, fatigue, or temporary illness.

With today’s technology there is no reason why we should not all have 20/20 vision, and the range of visual aids and treatments means we can find a way to correct our vision that fits our lifestyle comfortably.

If you are experiencing difficulty reading the small print, or seeing properly at night, don’t hesitate to make an appointment with us at Sun Valley Optometry. Squinting and straining to see causes eyestrain and headaches, but more importantly, loss of vision can impair your ability to drive and that can have serious consequences.



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