What Do Those Numbers Mean? How To Read Your Eyeglass Prescription

4 January 2016
 Categories: , Blog

If you've been to the optometrist and are told you need glasses, you probably received a complicated-looking prescription. The prescription may look like a bunch of strange numbers and abbreviations that looks like a mathematical formula. However, it's actually not complicated to figure out what these numbers mean and how they relate to your vision. Here are some common prescription terms and what they mean.


Sphere refers to the shape and power of the lens and is measured in diopters. The sphere is used for the overall lens and is either positive, for farsightedness or negative for nearsightedness. The larger the diopter, the more correction is needed. For example, a diopter of 1.00 is mild, while one that is 5.00 is more severe. These numbers don't directly translate into visual acuity. While someone may have 20/40 vision and need a -1.00 lens, someone else needing the same type of lens may have 20/100 vision.


Cylinder refers to the amount of correction needed for astigmatism. Astigmatism is an imperfection in the shape of the cornea that can affect visual acuity. If you have no or only mild astigmatism, your prescription might not have a number for this column. Like sphere, cylinder measurements are listed in diopters.


Axis refers to where your astigmatism is on your eye and tells the lens maker the direction of the imperfection. Eyes are divided up into meridians ranging from 1 to 180 degrees. The number of your axis, if you have astigmatism, refers to the position of the astigmatism on that meridian. The lens will be modified to correct the astigmatism in the area where it occurs.

Add and prism:

The add column is used if you need bifocals and usually refers to magnification around the bottom of the lens. The number is almost always positive and is the same for both eyes. Prism refers to a small raised area on a lens to help with unusual problems such as alignment issues, lazy eye or crossed eyes. It convinces the brain that the eyes are working together and helps solve problems with double vision.

If you have a simple prescription, chances are you will only have a number for sphere and nothing else. As your eyes change, you may see other numbers appear on your prescription. Often, the more complicated the prescription, the more precise it will have to be in order to eliminate distortions. See your optometrist and optician any time you feel that your prescription is not working for you.

To learn more, contact a company like Eye Tech Optical