Click on more info to Add to cart and more

20/20 vision explained

20/20 vision explained

The 20/20 scale measures the sharpness of a person’s vision. To test your vision, an eye doctor will place a chart 20 feet away and ask you to read the letters starting with the large capital E at the top and continuing down ten rows of letters. If you have normal 20/20 vision, you can read the first 8 rows of letters from 20 feet. If you have 20/50 vision, you can see at 20 feet away what a person with normal vision sees at 50 feet. And so on.

No matter your number, with the proper vision correction, such as prescription eyeglasses or contact lenses, you can improve your vision and see the world in all its beauty.

In Europe and some parts of Canada, they do not use 20/20 as the base measurement of visual sharpness. Instead, they use 5/5 or 6/6, reflecting the usage of the metric system.


When you receive your prescription, you’ll be given a number for every category that requires attention. This number represents diopters, a unit used to measure the lens power needed to correct your vision. When learning how to read your eyeglass prescription keep in mind that usually the further from zero the numbers are, the worse your eyesight is. A plus or minus sign in front of your prescription number indicates what type of sight problem you have. If there is a plus, it means you’re farsighted or have blurred near vision. If there is a minus, it means you’re nearsighted, meaning you have blurred distant vision.

Making sense of numbers
Prescription terms and letters


There are many different abbreviations and terms used in eye prescriptions which can make learning how to read an eyeglass prescription confusing. Remember, the information is typically written in a grid with the abbreviations SPH, CYL, AXIS, and PRISM written across the top row, and with ADD, O.D., O.S., and O.U. written down the left column. “ADD” is added magnifying power in the bottom of a multi-focal lens to correct presbyopia, the inability to focus on close objects. "O.D.," "O.S.," and "O.U." are abbreviations for oculus dexter, oculus sinister, and oculus uterque, the Latin terms for right eye, left eye, and both eyes.

Your eyeglass prescription explained:

•  SPH(or Sphere) indicates the prescription power, or how strong your lenses need to be to correct your vision. For an indicator of how much magnifying power is needed in a bifocal or progressive lens to correct your vision problems, look for ADD.

•  CYL (or Cylinder) denotes astigmatism, a condition where the cornea is irregularly shaped causing blurred or distorted vision. It also tells the lens strength needed to fix it.

•  AXIS describes the degree and direction of your astigmatism.

•  PRISM tells you the amount of prismatic power needed to correct eye alignment problems. However, only a small percentage of eyeglass prescriptions have this.

Once you understand how to read your eyeglass prescription, it’s easier to see what your prescription says about your vision. Make sure to have your eyes evaluated each year to ensure your prescription eyewear is up to date—so you always have a crisp, clear view of the world. Schedule your annual eye exam* today.