How to Read an Eyeglass Prescription

If you need eyeglasses, you might be confused by the numbers, terms, and symbols on your prescription. However, there are important reasons why it's 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 use a sample eyeglasses prescription to walk you through how to read your own.

Latin Abbreviations

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

On your prescription, you might see abbreviations for specific terms instead.

For example, the word "power" is sometimes written as "PWR." Another common term is "sphere" which is sometimes abbreviated as "SPH" on a prescription.

Here's what the Latin abbreviations on the example prescription mean:

• OD stands for "oculus dexter" and refers to the right eye.
• OS stands for "oculus sinister" and refers to the left eye.
• OU stands for "oculi uterque" and refers to both eyes.

What Do The Numbers Mean?

In addition to terms and abbreviations, eyeglasses prescriptions also include a lot of numbers.

You'll also see some mathematical symbols like the plus sign (+) and minus sign (-).

Sphere

In the example prescription, the first number to the right of OD is -2.00. This is the "sphere" part of the prescription, which may be abbreviated as "SPH."

The sphere number indicates whether you have nearsightedness or farsightedness.

Nearsighted people have trouble seeing things that are far away. Farsighted people have trouble seeing things that are up close.

You'll also see a plus sign or minus sign before the number.

• A minus sign (-) means you need a negative-powered lens. These lenses are used to correct nearsightedness.
• A positive sign (+) means you need a positive-powered lens. These lenses correct farsightedness.

Cylinder

The next number in the sample prescription is -0.50. This is the "cylinder" measurement. On your prescription, "cylinder" might be abbreviated as "CYL."

The cylinder measures the degree of astigmatism in your eye. The number shows how much lens power will be needed to correct astigmatism.

Axis

The next number is x 180, which is read as "axis 180." 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 eye.

The cornea is the clear covering of your eye. It is the part of your eye that does most of the focusing.

In the example, the left eye's "sphere" number is plus one (+1.00) DS.

The letters DS mean "diopters sphere." This number means the left eye’s correction is spherical with no astigmatism.

In other words, the right cornea probably has a slightly oblong shape while the left cornea is very close to being perfectly round.

ADD Number

In the example, the ADD number of +1.75 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.

In the above example, for the right eye, this would be -2.00 and +1.75, which equals -0.25. For the left eye, add +1.00 and +1.75 to get +2.75.

Next, look at the cylinder measurement and the axis measurement.

In the example, the correct number for the right eye is -0.25 -0.50 x 180 while the correct number for the left eye is simply +2.75.

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.

Summary

Your eyeglasses prescription may include Latin abbreviations, numbers, and mathematical signs. These numbers are used to describe the shape of your eye and the correction you need in your glasses.

For example:

• OD and OS refer to the right and left eye.
• SPH shows if you have nearsightedness or farsightedness.
• CYL and AX/X numbers note if you have astigmatism.
• ADD indicates the amount of correction that will need to be "added" to your prescription for reading.
• PD is the distance between your pupils; this number ensures that your glasses are the right fit for your face.

If you're confused about what the words and numbers on your prescription mean, ask your eye healthcare provider to explain them to you.