How to Read an Eyeglass Prescription

Your eyeglasses prescription can look a little confusing. There are good reasons, though, why it is written the way it is.

An eyeglasses prescription needs to be readable no matter where you are in the world. This is why most eyeglasses prescriptions use the same standard format and common notations.

The article looks at a sample eyeglasses prescription. It also walks you through how to read your own prescription.

Latin Abbreviations

Most eyeglasses prescriptions use Latin abbreviations. Latin is often used in healthcare to write prescriptions.

These abbreviations are becoming less common. This is because state and federal rules are starting to reduce dependence on them. Because of this, not all prescriptions will look like the example below.

How to Read an Eyeglass Prescription
Verywell / Alex Dos Diaz

Example Prescription

OD: -2.00 – 0.50 x 180

OS: +1.00 DS

ADD: +1.75 OU

Abbreviations used:

  • The letters OD stand for "oculus dexter." This refers to the right eye.
  • The letters OS stand for "oculus sinister." This refers to the left eye.
  • The letters OU stand for "oculi uterque." This refers to both eyes.

What Do The Numbers Mean?

Eyeglasses prescriptions contain a lot of numbers. Here's what they mean.

Sphere

In our example above, the first number to the right of OD is -2.00. This is the "sphere" part of the prescription. The sphere number indicates nearsightedness or farsightedness.

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

  • Generally, a minus sign (-) means you need a negative-powered lens. This is used to correct nearsightedness.
  • A positive sign (+) means you need a positive-powered lens. This is used to correct farsightedness.

Recap

OD and OS refer to the right and left eye. The sphere measurement indicates nearsightedness or farsightedness.

Cylinder

The next number in the sample eyeglasses prescription is -0.50. This is the "cylinder" measurement. It measures the degree of astigmatism in your eye. The number describes the amount of lens power that will be needed to correct your astigmatism.

Axis

The next number is x 180. It is read as "axis 180." It indicates an angle in degrees from 0 to 180. If you have astigmatism, this number points to its location on your eye.

For the left eye in the above example, the "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. The left cornea, however, is very close to being perfectly round.

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

It is common to write SPHERE or DS as a place holder where the astigmatism number’s goes. This ensures the reader knows the doctor did not forget to record the cylinder or astigmatism correction.

ADD Number

Finally, the ADD number of +1.75 represents the power that needs to be "added" to the distance prescription. This will give the patient clear vision for reading and other close activities.

Younger people's prescriptions don't usually have this number. Some young people can have near focusing problems, but it usually develops as you approach 40.

Some people think the ADD number is the power needed for over-the-counter reading glasses. It is not the same number, though. To get the right number, you need to do additional calculations.

To find the right reading glasses, add the sphere number to the ADD number. In the above example, this would be -2.00 and +1.75 with the result -0.25.

The cylinder measurement comes next, followed by the axis measurement. So for the right eye, the correct number is -0.25 -0.50 x 180. For the left eye, add +1.00 and +1.75 to get the result +2.75.

Most people have prescriptions that aren't like the example. The numbers are usually similar in power for both eyes.

The example was chosen to show the difference between nearsighted and farsighted prescriptions.

Recap

The ADD number is the power that needs to be added to the prescription for reading and other close work. It is not the same as the number you would use to shop for a pair of reading glasses.

Other Abbreviations You May See

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

  • SVD: Single vision distance. These are glasses for distance vision correction only.
  • SVN: Single vision near. These are glasses for reading only.
  • SPH or Sphere: This refers to the strength of the lens.
  • Cylinder: Cylinder power corrects astigmatism. This number is the difference between the greatest power of the eye and weakest power of the eye.
  • Axis: Points to where the correction for astigmatism is needed.
  • PD or Pupillary Distance: This is the distance between the centers of the two pupils. This measurement is essential for glasses that are comfortable and optically perfect.
  • Prism: Prism is not common. This measurement usually applies to patients with crossed-eye 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 and numbers. These numbers are used to describe the shape of your eye and the correction you need in your glasses.

OD and OS refer to the right and left eye. The sphere number describes nearsightedness or farsightedness.

Your prescription may also include cylinder and axis numbers. These numbers describe astigmatism. ADD refers to the correction that will need to be added for reading.

Your prescription may also include other abbreviations, like PD. This is the distance between your pupils. It helps ensure that your glasses are the right fit.

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3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Vimont C, Turburt C. What do astigmatism measurements mean? American Academy of Opthomology.

  2. MedlinePlus. Presbyopia.

  3. Porter D. What is prism correction in eyeglasses? American Academy of Opthomology.

Additional Reading
  • Eskridge, J. Boyd, John Amos and Jimmy D. Bartlett. "Clinical Procedures In Optometry." Copyright 1991 by J.B. Lippincott Company, Chapter 18 - "Monocular Subjective Refraction" by Polasky Michael, pp 174-188.