How to Read Your Eyeglass Prescription

If you have less than perfect vision, you might be wondering how to read your glasses prescription. There are a variety of numbers, terms, and symbols on the prescription, and it can be difficult to know what they mean. However, there are important reasons why the prescription is written the way it is.

Eyeglasses prescriptions use the same standard format and common notations. This makes them universal, meaning that they can be read anywhere in the world.

The article will help you decipher an eyeglass prescription by walking you through what the terminology means.

OD vs. OS

Providers who write eyeglasses prescriptions may include Latin abbreviations. While they have been used for a long time, Latin abbreviations are becoming less common.

OD is an abbreviation for the Latin term oculus dexter and refers to the right eye. OS is an abbreviation for the Latin term oculus sinister and refers to the left eye.

Sphere (SPH)

Sphere is abbreviated as "SPH" on a prescription and indicates whether you have nearsightedness or farsightedness.

Nearsighted people have trouble seeing things that are far away. Farsighted people have trouble seeing things at all ranges.

Cylinder (CYL)

The next number is the "cylinder" measurement. On your prescription, "cylinder" might be abbreviated as "CYL."

The cylinder measures the amount of astigmatism in your eye. The number shows how much lens power will be needed to correct astigmatism. If there's no CYL number on the prescription, that means your healthcare provider hasn't found an astigmatism that needs to be corrected.

Axis (AX or X)

On your prescription, "axis" is sometimes abbreviated as "X" or "AX." This number is an angle in degrees from 0 to 180. If you have astigmatism, this number points to where it is in your cornea, which is the clear covering of your eye. It is the part of your eye that does most of the focusing.

ADD Number

The ADD number notes how much power needs to be "added" to the distance prescription. This addition helps a person see better for reading and other activities that they do up close.

Younger people's prescriptions usually do not have an ADD number. While some young people can have near-focusing problems, it usually develops as you approach 40.

ADD vs. Powers for Readers

Some people think the ADD number is the power needed for over-the-counter (OTC) reading glasses (or "readers"), but it's not the same thing.

To get the right number, you need to do a little math.

To find the right reading glasses, add the sphere number to the ADD number. Next, look at the cylinder measurement and the axis measurement. Astigmatism is typically not corrected in over-the-counter reading glasses.

Other Abbreviations

You may also see a few other words or abbreviations on your eyeglasses prescription:

• SVD: This means you only need glasses for single vision distance (for distance vision correction only).
• SVN: This means you only need glasses for single vision near (for reading glasses only).
• PD (pupillary distance): This is how much space there is between the centers of the two pupils of your eyes. This measurement is how your provider makes sure that your glasses are comfortable to wear and optically perfect.
• Prism: This measurement usually only applies to people with crossed eyes (strabismus) or other eye muscle or focusing disorders. In glasses with this measurement, the image in the lens is displaced in a certain direction.

What Do the Numbers Mean?

In addition to terms and abbreviations, eyeglasses prescriptions also include a lot of numbers. These numbers indicate how much correction your vision needs. The higher the number, the more correction your vision needs.

One of the numbers, the axis, refers to the location of your astigmatism. If you don't have astigmatism, you won't see an axis number.

Nearsighted vs. Farsighted Prescription

You'll also see some mathematical symbols like the plus sign (+) and minus sign (-). The plus sign refers to farsightedness and the minus sign refers to nearsightedness.

Being nearsighted means that you can see closer objects better than ones that are far away. This happens when light focuses in front of the retina instead of on it, possibly due to the shape of your eyeball or cornea.

If you are farsighted, distant objects appear clearer than closer ones. This happens when light focuses behind the retina instead of on it, again due to the shape of your eyeball or cornea.

Your glasses will be designed to correct your specific problem. The greater the number next to the plus or minus sign, the more correction you need.

Summary

Your eyeglasses prescription may include Latin abbreviations, numbers, and mathematical signs. These numbers are used to describe the correction you need in your glasses. A plus sign next to the number means you are farsighted, while a minus sign means nearsightedness. The higher the number, the more correction your vision needs.