20/20 Vision: understanding what it means

 

 

If you have 20/20 vision  this is good news, but it does not  mean you do not need to see your eye doctor regularly. First, what does 20/20 vision really mean?

Visual Acuity: What is 20/20 Vision?

 

Normal acuity

Normal vision is known as “20/20 vision”. This defines normal visual acuity (the clarity or sharpness of vision) that is measured at a 20-foot distance.

To determine your visual acuity, your eye doctor uses an eye chart. To evaluate if you see well enough to drive, the DMV uses the eye chart as well. The top number refers to your distance in feet from the chart. The bottom number indicates the distance at which a person with normal eyesight can read the same line.

If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance.

Better acuity

Except for very rare cases, the best possible  visual acuity in humans is a 20/10 vision. Using the same formula, it means that you can clearly see at a 20-foot distance what a “normal” person can only see at 10 feet.

Lower acuity

The bigger the bottom number the less clear is your vision. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet. People with a vision of 20/200 or worse have remaining sight, but very poor acuity. They will be classified as legally blind.

In addition, some people  can see well at a distance but cannot see clearly objects that are close and are unable to read without glasses. This is due to either hyperopia (also called farsightedness), or presbyopia that occurs with age. In other cases, people can see well at a short distance but not from far away. This is  nearsightedness/ myopia.

The purpose of corrective lenses (glasses and contacts) is to bring your vision to 20/20 whenever possible.

I have 20/20 vision. Does it mean I see perfectly?

 

However, having 20/20 vision does not necessarily mean you have perfect vision. It is only an indication of how sharp and clear your vision is.  There are many other factors that your eye doctor uses to determine the quality of your vision:

  • Peripheral vision
  • Eye coordination
  • Eye focusing
  • Perception of depth, as well as
  • Color vision

Here are some conditions that the eye chart will not detect:

  • Convergence insufficiency: when looking at close objects (such as reading) both eyes are not working together as they should. It often promotes eye strain, blurred vision, headaches and even double vision.
  • Focusing problems: it usually happens when doing detailed work or when having to shift from near to far quickly. The vision can get blurry and the eyes tired. 
  • Strabismus:  or “crossed eyes” in common language, is due to the misalignment of one or both eyes.
  • Photophobia:  is a hypersensitivity or even an inability to tolerate light. With a lot of exposure to blue light from LED lights and digital devices, the eyes can become  more and more sensitive and develop dryness and other issues.

Visual acuity versus eye health

 

Additionally, keep in mind that eyesight and eye health do not necessarily go hand in hand together. In other words having 20/20 vision does not guarantee that your eyes are healthy.  For example, a progressive eye disease such as glaucoma can start to develop without your noticing any signs. The same is true about early stages of  age related macular degeneration. Both conditions can lead to partial or total blindness. Only a thorough eye exam will determine whether your eyes are in good health or need some help.

Get a complete eye exam

 

The assessment of your visual acuity is only one part of your eye exam. If you are over 40, regular vision screenings are important but not sufficient. This is the moment when signs of diseases or other eye conditions can start to show. You should get a comprehensive eye examination that may catch these problems early on, and allow your doctor to take care of them before it is too late.