Why 20/20 Vision May Not Be 'Perfect' - Smart Vision Labs

We have all heard the term ’20/20 vision’ but if you have it, does that mean your eyesight is perfect?

The answer is both yes and no, and no, this isn’t confusing. In fact, after reading about it, you will see your vision in a different way.

Let’s start with the term 20/20. The familiar on-the-wall eye chart checks your vision acuity, which is the sharpness of your vision. The letters on the chart are a specific size to measure your ability to see them at a certain distance.

In the term ’20/20′ the first number is the distance from the wall chart to the patient. The chart is positioned 20 feet in front of you.

The second 20 refers to your ability to read the letters. Each line of letters is a specific size which has been determined through a mathematical study of what normal vision should be. For instance, to have a rating of 20/20 means that you can easily read the fourth line from the bottom of the chart.

Interestingly, if you can read the letters below that line your vision would be ‘better’ than 20/20 and may be even 20/10 or 20/5 although not many people have this ability.

Although there is a solid mathematical base for this eye chart, having 20/20 vision does not mean that your eyesight is perfect in all situations.

The wall chart test is limited in several ways. First of all, it’s a static measurement. You sit still during the test and the chart is not moving. Real life is anything but still, which means your eyes are constantly focusing on objects that are in motion.

The eye chart also uses high contrast conditions to check your vision acuity. Usually, the letters are black against a white background. Once again, life is not limited to these conditions. Having 20/20 vision does not determine that you see well in dim situations, like night driving.

In a similar thought, the eye chart doesn’t measure if you see colored or moving objects normally either.

Because of the limitations of the eye chart, other tests should be taken into consideration at your next eye exam. The actual physiology of the eyes should be examined, through scans or photos. This information, combined with the vision acuity test, can better determine if you would see clearer with corrective glasses.

These additional tests would evaluate other key areas that affect vision. In large part, the clarity of your eyesight is dependent on how light travels through your eyes and whether it focuses on the retina. Vision is also affected by the sensitivity of the nerves in the retina and how the brain interprets the information received from the eyes. An eye chart alone cannot assess these things, but it will give you an excellent basis for you and your eye doctor to examine your vision and begin to diagnose any abnormalities.

While 20/20 is the standard by which vision is measured and the basis for most prescription lenses, having this designation does not tell the whole story about your eyes.

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