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How To Read Prescription

We understand that many look at their prescriptions and see only a confusing jumble of numbers, symbols, and abbreviations. The following guide will help you decipher this important information.

Here are some examples of how your prescription might look:
Example 1:

Example 2:

Example 3:
R: -3.75 / -1.25 x 178
L: -3.75 / -1.50 x 180

First, let’s translate the abbreviations.

O.D. = right eye. In example 1, the top row contains measurements for the right eye.
O.S. = left eye. In example 2, the bottom row contains measurements for the left eye.
SPH = SPHERE power, or the main correction power which corrects refractive error.
CYL = CYLINDER power corrects astigmatism refractive error.
AXIS = shows where an astigmatism is located along the eye’s horizontal axis.
ADD = the amount added to the sphere (SPH) value for those requiring reading glasses, bifocal or progressive lenses.
PRISM = indicates the image’s displacement value through the lens for those with unusual conditions like a squint or lazy eye.

Some other abbreviations you might see:

D.S. or DS = diopters sphere which indicates that you have only a sphere value and no cylinder value; therefore you need no correction for astigmatism.
D.V. = distance vision
N.V. = near vision, sometimes written as N.V.O.
O.U. = both eyes
X = axis
P.D. = pupillary distance

Further information

SPH / SPHERE
All prescriptions have this measurement and this indicates the strength of your prescription in increments of 0.25. It is measured in diopters for either nearsightedness (myopia) or farsightedness (hyperopia). The number is sometimes written without the decimal point. For instance, 150 is 1.50.

Often the + or – sign is written above the number, so please check and select these signs carefully. You might also find an infinity (∞) symbol, Pl or PL in the sphere column. When ordering your glasses please select the ‘infinity’ or ‘plano’ option in the drop-down menu. In the prescription example 3, -3.75 is the sphere value for each eye.

CYL / CYLINDER

If you have an astigmatism, your prescription will have a number in this column. The number should be between +/-4 and in 0.25 increments. It’s common for the cylinder value to be the same for both eyes.

For any cylinder value provided, there will always be a value for axis.
There’s a huge difference between a positive (+) and negative (-) cylinder, so pay close attention when ordering, and select the correct sign.

In prescription example 2, the person has a -0.25 cylinder value for both distance and near vision. Sometimes the optometrist will leave out the decimal point, and you might find the negative symbol written above the number and not before it.

If you find a ‘DS’ or ‘SPH’ in the CYL column, this means that you have no astigmatism and hence no cylinder value, only a sphere power in your prescription. In this case, select the ‘CYL none’ option in the drop-down menu.

In example 3, the person has a -1.25 cylindrical value in the right eye and a -1.50 cylindrical value in the left.

AXIS

If you have astigmatism, the axis value indicates where your astigmatism is located along your eye’s horizontal axis. Not all prescriptions have axis and cylinder values; however if you have astigmatism you should have both of these values on your prescription. The axis number will be between 1-180 degrees, and it should always be a whole number - there should be no decimal point.
In example 3, the person has an axis value of 178 in the right eye, and 180 in the left eye.

ADD / NEAR ADDITION

This value can be written anywhere on the prescription. It indicates the amount to be added to the SPH value for reading, intermediate glasses or computer work. If you can only find one ADD value, this means that your ADD is the same for both eyes. If you find two figures, then you have a different ADD value for each eye.

If your prescription has a completely separate column for ADD, this means that this measurement is for the lower or reading section of your bifocal lenses.

PRISM and BASE

The prism and base sections are usually left empty, as they are not commonly seen on most prescriptions. Prism is used to treat people with a muscular imbalance or other conditions like a squint or lazy eye. While the prism value refers to the displacement of the image through the lens, the base value refers to the direction of this displacement.

Please enter your prism and base information into the ‘Any extra information’ box when ordering online.

BALANCE

If there is little or no vision in one eye, the optician might write ‘balance’ on your prescription to ensure that your lenses are a similar weight and thickness for cosmetic reasons.

If you have this written on your prescription, please enter this information in the ‘Any extra information’ box.

Extra tips

• For distance correction, most of the time the value under sphere is negative.
• For reading-only correction, most of the time the value under sphere is positive.
• Please ensure that you get the + or – symbol correct. This will make a huge difference to the accuracy of your lenses.
• If some of the boxes on your prescription are blank (e.g. no CYL or AXIS or ADD values), leave those boxes blank when ordering.
• If you have a value under “Near Vision” (N.V., N.V.O.) then enter the power in the BOTTOM half of the form and leave the ADD power blank or ("0.00").
• For bifocal and progressive lenses, please check with your optometrist whether the Addition (ADD) value is for bifocals or progressives.
• Sometimes optometrists will leave out the decimal point on the Sphere, Cylinder and Addition values. For example, -25 is understood as -0.25, and +175 is +1.75.
• If you see a PAL note written on the prescription, then this simply indicates that your prescription is for PROGRESSIVE lenses.
• Please be advised that we process a minimum of +1.00 and maximum of +3.00 for ADD powers.

If there is anything else on the prescription that you are confused about, please call or e-mail our Customer Service and we’ll be happy to assist you.

Pupillary Distance Measurement

Pupillary Distance is the distance between the center of one pupil (the central black dot of your eye) to the center of the other pupil. Measured in millimeters, PD is important as it helps the laboratory technician to accurately create your eyeglasses frames by lining up your pupil with the center of the lens. As for obtaining your PD measurement, eye doctors are generally not legally obligated to give you this as it’s technically not part of the eye test itself, but something measured for the purpose of creating eyeglasses frames.

So if for some reason you can’t obtain the PD measurement from your optometrist, you have the option of measuring it yourself:

Step 1

Stand 20cm in front of a mirror (or with a friend facing you), and place a millimeter ruler on the bridge of your nose so that the ruler’s ‘0’ measurement is exactly in line with the center of your left pupil. Keep the ruler straight.

Step 2

Read the measurement in the mirror’s reflection (or let your friend read it) between the left pupil and the right pupil while you look straight ahead.

Step 3

Repeat this a few times for accuracy.

Your final option is simply to use an average PD measurement, which is the least accurate method. Most adults have a PD distance ranging between 57-65mm. For single vision lenses, adults have an average pupillary distance of 62mm. In the event that you cannot obtain your own pupillary distance from your optician or measure it yourself, it’s satisfactory to use this average PD measurement, but please remember that this is the least accurate option.

For those requiring bifocal or progressive lenses, we strongly recommend you get this information directly from your optician. After you receive your PD from the optician, you may notice there are two different values. If you have the numbers ‘65/60’ for example, the first PD is usually for distance vision and the second number is for near vision or reading.