How to read an eyeglass prescription

Reviewed by: Dr. Matthew Miller, OD on May 6th, 2020

Knowing how to read an eyeglass prescription is essential! While you likely know whether you’re nearsighted, farsighted or have astigmatism, determining that from your prescription slip is another thing entirely. That’s why we’ve put together a short guide to help you learn how to read your eye prescription so you can get to ordering your new set of eyeglasses as quickly as possible.

How to Read an Eyeglass Prescription

If you complete an eye exam and find your eyes’ needs have changed, you need to order a new prescription as soon as possible. That’s where your new prescription from your optometrist or ophthalmologist comes in.

Most online retailers ask you to read and input your prescription into their order form, but if you don’t know how to read your prescription, that process can get complicated.

What do all these letters and numbers mean?

The numbers on your eyeglass prescription describe precisely how your glasses lenses should be cut. Keep your prescription up to date so these numbers can accurately reflect your visual needs. Typically, you’ll see several abbreviations and words labeling all of the important data on your prescription. See below to learn the meaning of SPH, CYL Axis, Prism, PD, and more.

  • Nearsighted prescriptions

    A nearsighted prescription will feature a number with a minus (-) symbol in the ‘sphere’ box. This means your lenses will be shaped to improve your distance vision.

    Glasses Prescription
    Patient Expiration date
    Distance OD
    OS
    Sphere Cylinder
    -4.00
    -5.00 -0.50
    Axis Prism
    180
    Base Add
    Pupilary distance (PD):62
    Additional information:
    Hover on the prescription form to find out what all those number and abbreviations mean
  • Farsighted prescriptions

    A prescription for someone who is farsighted will feature a number with a plus (+) symbol in the ‘sphere’ box. This indicates that your lens should be shaped to correct near vision.

    Glasses Prescription
    Patient Expiration date
    Distance OD
    OS
    Sphere Cylinder
    +2.00
    +2.00 -0.50
    Axis Prism
    180
    Base Add
    Pupilary distance (PD):62
    Additional information:
    Hover on the prescription form to find out what all those number and abbreviations mean
  • Astigmatism prescriptions

    If you have an astigmatism, you will have a number in the ‘cylinder’ column of your prescription that indicates the lens power needed to correct the astigmatism. There will also be a number in the ‘axis’ column that’s needed for astigmatism correction.

    Glasses Prescription
    Patient Expiration date
    Distance OD
    OS
    Sphere Cylinder
    -4.00
    -5.00 -0.50
    Axis Prism
    180
    Base Add
    Pupilary distance (PD):62
    Additional information:
    Hover on the prescription form to find out what all those number and abbreviations mean
  • Bifocal & progressive prescriptions (multifocal)

    A multifocal prescription will include an ADD value, sometimes marked as NV. This indicates the required strength for the near prescription in your lens.

    Glasses Prescription
    Patient Expiration date
    RX
    Multifocal OD
    OS
    Sphere Cylinder
    -4.00
    -5.00 -0.50
    Axis Add
    +2.00
    180 +2.00
    Pupilary distance (PD):62
    Near PD:59
    Additional information:
    Hover on the prescription form to find out what all those number and abbreviations mean
  • Prescriptions with prism correction

    A prescription for correcting eye alignment issues will include a PRISM and BASE value. These are needed to tell us how to shape the lens so that it can accurately align the wearer’s eyesight. The base value will show either “in” or “out”, or “up” and “down”, indicating the direction the prism should be angled.

    Glasses Prescription
    Patient Expiration date
    Distance OD
    OS
    Sphere Cylinder
    -4.00
    -5.00 -0.50
    Axis Prism
    180
    Base Add
    down +2.00
    up +2.00
    Pupilary distance (PD):62
    Additional information:
    Hover on the prescription form to find out what all those number and abbreviations mean
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How often should you get an eye exam?

If you don’t have any medical issues that affect your vision, you should have a comprehensive eye exam every one to two years.

Children should have their first eye exam when they are around six months old, and then another just before they start school. This ensures that they can see clearly in class; poor vision can seriously impact a child’s learning

FAQ

What do ‘OD’ and ‘OS’ mean?

‘OD’ and ‘OS’ are abbreviations of the Latin words ‘oculus dexter’ and ‘oculus sinister’, respectively. In the context of an eye prescription, ‘OD’ means ‘right eye’ and ‘OS’ means ‘left eye.

What does Sphere, Cylinder and Axis mean?

In the context of an eye prescription. ‘Sphere’ is basically a measure of how strong your prescription needs to be. The number marked ‘axis’ describes the orientation of astigmatism. It will be a number between 1 and 180. The number under ‘cylinder’ provides the lens power needed to correct the astigmatism.

What does ‘base’ mean on an eye prescription?

Your prescription may have a ‘base’ column, or it may be included in the same column as ‘prism’ this gives further information about the required prism correction, telling us the orientation needed in the lens.

What does ‘add’ mean on an eye prescription?

The number under the ‘add’ column tells us the 2nd lens prescription needed for multifocal lenses.

What is a strong eye prescription?

The higher the number on your prescription, the stronger your prescription is. A number with a minus symbol before it means you are nearsighted, and a number with a plus symbol, or no symbol, means you are farsighted. A number over 5 is generally considered to be on the stronger side.

What is an astigmatism?

If you have an astigmatism, indicated by an “axis” and “cylinder” number on your prescription, it means that the front of your eye is irregularly shaped. This stops light from focusing properly on your retina and makes your vision blurry. It usually occurs along with near or farsightedness.

Is astigmatism hereditary?

Astigmatism is often present at birth, but it can develop, or become more severe, as you get older.

What is a diopter count?

Diopter is the measurement used for the strength of eyeglass lenses. The number under the ‘OD’ and ‘OS’ measurement in your prescription is measured in diopters.

Now that you understand those mysterious letters and numbers, you know how to read a glasses prescription! Knowing what they mean will also help you more easily discuss your prescription with your eye care professional.

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