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How to Read a Glasses Prescription?

Reviewed by: Henry from Basames on 2019-01-21
  • 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 a glasses prescription so you can get to ordering your new set of eyeglasses as quickly as possible.

    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.

    OD vs. OS Eye

    OD is short for the Latin term oculus dexter which means right eye.

    OS is an abbreviation of the Latin oculus sinister which means left eye. You’ll often see this terms on eyeglass prescriptions.

    Sphere, Cylinder, and Axis on Eye Prescriptions

    Sphere: The sphere (SPH) on your prescription indicates the lens power you need to see clearly. A minus (-) symbol next to this number means you’re nearsighted, and a plus (+) symbol means the prescription is meant to correct farsightedness.

    Cylinder: The cylinder (CYL) number indicates the lens power needed to correct astigmatism. If this column is blank, it means you don’t have an astigmatism.

    Axis: An axis number will also be included if you have an astigmatism. This number shows the angle of the lens that shouldn’t feature a cylinder power to correct your astigmatism.

    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.

    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.

    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.

    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.

    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.

    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.

    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.

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