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    If you’ve ever looked at your prescription and wondered what the bunch of numbers on it meant, there’s help at hand. Grab a copy of your prescription and we’ll explain all the terms so you can understand the values and what they mean.

    Note: Before we get started: please ensure that you have a copy of your eyeglass prescription and not your contact lens prescription as the two are usually a bit different. Do NOT use your contact lens prescription to order eyeglasses!


    On a typical prescription, you will see two sets of rows. Usually, the top portion is for your Right Eye (OD) and the bottom portion is for your Left Eye (OS). These will be clearly marked.

    Standard layouts of prescriptions are as given below:

    Understanding the Various Terms:

    Click on any link below to see what the term means




    ADD or Near Addition

    Understanding your PD

    Measuring your PD


    The sphere value (SPH) determines the strength of the lens, and therefore its thickness. The SPH is in 0.25 increments. For distance correction (Short-Sightedness), there is usually a value under sphere (SPH) and it is marked as negative (-). The abbreviation is “D.V.” or Distance Vision.

    Opticians often indicate negative values by putting a dash above the number. If the sphere reading is negative in one eye then it is normally negative in the other eye and vice versa.

    It's normally a number between -15 to +15. eg, -1.75. some opticians don't include the decimal point eg, -175

    In this box you may also see the following signs:

    This sign is quite common and looks like an 8 on its side but it stands for ‘infinity’. Sometimes ‘PL’ is used instead. You should select the value 0.00 in the drop down if you have Plano on your prescription.


    The cylinder value determines the strength of the astigmatism correction. It should be a number between -4 to +4, in 0.25 increments.Doctors will often use positive (+) cylinder but some use negative (-), there is a BIG difference between the two so please pay close attention to the signs.

    Not all prescriptions have Cylinder (CYL)/AXIS values. If you do not have astigmatism correction, doctors may leave it blank but they might also put SPH, 00, Plano, or DS which means sphere or Diopter Sphere.

    If fill your prescription online you can enter either nothing (leave the column blank), or select the value 0.00 in the drop down.


    The axis value is the angle of the astigmatism correction.

    Please note that that Cylinder (CYL) and Axis are always provided together. For any value of Cylinder there should always be a value for Axis. Axis should be from 1-180 degrees. If you see a number like ‘6’ under axis, it is also the same as ‘006’ or ‘6 degrees.’ It should always be a whole number and never with a decimal point on the axis.
    Please note: when inserting your axis into the field provided, only insert a number like 6 instead of 006.

    ADD or Near Addition

    The Add concerns bifocal/progressive reading and near correction.

    Sometimes opticians write the addition as a complete additional line on your prescription, sometimes once (same for both eyes) and sometimes once for each eye. Only one ADD means that the addition for both the left and right eyes are the same.


    This person has an Add of +2.75, which should be put in for both eyes

    Opticians write this all over the prescription, sometimes once (same for both eyes) sometimes once for each eye.


    If you are ordering bifocal or progressive glasses please make sure you enter your ADD measurement as a separate reading in this box.
    OR ELSE If you have a prescription for bifocal glasses but want to purchase single-vision lenses for distance correction only, leave this field blank and do not enter the value for ADD.

    Understanding your PD

    In order to create glasses that fit you best, we need to create lenses that can match the distance between your eyes, so the center of each lens aligns with the center of your pupils. For this reason, we need your pupillary distance measurement – also known as the PD measurement.

    Unfortunately, many opticians don’t include your PD in the prescription. We suggest that you either ask your optician for your pupillary distance measurement or if you would prefer not to, we can make your glasses using an average pupillary distance measurement . While it works well for most customers, it can cause discomfort or strain for others. If you have a strong prescription or your PD is significantly differently from the average, you may experience some problems with eyeglasses that have the average PD measurement.

    Average PD is about 63mm and most people fall within the 54 to 74 range. If your number is outside this range, you may have made a mistake. Please do not guess or assume your PD.

    Occasionally, PD is written like 32/34.5 (for example), which means the measurement from the center of the nose to either eye plus your PD is the sum of the two – 32+34.5=66.5 (Mono R + Mono L = PD) and you can enter this as 66 or 67.

    You may also be able to get your PD from a previous optician. Unlike a prescription, your PD does not expire with age. Opticians are required, under federal law, to give you your PD as well as your full prescription.

    Pupillary distance CAN be measured on your own with a tape measure.

    To measure your PD:

    1. Place the millimeter ruler on the bridge of your nose.
    2. Have a friend face you about arms length away.
    3. Have your friend measure the distance between the center of your pupils (the black dots in the middle of your eyes).
    4. (Or you can do it yourself simply by looking in the mirror).

    Download a printable ruler here (pdf).

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