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How do I read my prescription?
An eyeglass prescription is written in a standardized format, however sometimes they can be hard to understand. Here is what the numbers mean:
Right And Left Eye
The letters OD (usually the top line of your prescription) and OS (usually the bottom line) in front of a prescription let us know which eye each row of numbers is for.
OD (Oculus Dexter) = right eye
OS (Oculus Sinister) = left eye
OU (Oculus Uterque, Oculus Unitas or Oculus Uniter) = both eyes.
(Note – PL = PLANO; a placeholder for the number zero)
SPH – Sphere or Spherical
The first number in the prescription is the Sphere (or Spherical) and it is the spherical refractive error (farsightedness or nearsightedness). When there is a minus sign in front of the SPH number, the patient is nearsighted (meaning they would need glasses to see things that were far away like the TV). A plus sign would indicate someone who was farsighted (meaning they had trouble reading a menu or their watch). People who are nearsighted would need “distance” glasses, and people who are farsighted would need “reading” glasses.
CYL – Cylinder
The second number in the prescription is the Cylinder and it is used to indicate a correction for astigmatism. (An eye that is no longer round but more like an egg or football shape). If there is no astigmatism, you may see a zero or the letters DS or SPH after the first number to let the optician know that the doctor didn’t just forget to write in the astigmatism. (Note: -75 = -0.75 // +125 = +1.25) If your prescription does not have an astigmatism correction just choose zero.
The last number in a basic prescription is the Axis or direction of the astigmatism. Astigmatism, a football-shaped eye, can be measured in any direction around the clock. The axis numbers indicate the orientation of the football shape. (Note: X = axis – sometimes written as X 80 or AXIS 080 – the number “80” is just used for this example, your number will probably be different).
There may be additional numbers in a glasses prescription. The ADD numbers denote the amount of power that gets added to the distance prescription (SPH) and is used to create your “reading-only” prescription for “readers” – or for the lower portion of bifocal and progressive lenses.
Note: Sometimes you might have a prescription that has “NV” on it. This means it is for Near Vision – or in other words, for reading glasses or “readers”. This means that the SPH power and the ADD power have already been added together by your doctor for your readers.
Otherwise it would be a “DV” prescription Distance Vision prescription and, if you wanted to make “readers” out of them, there would be an ADD number and our lab would do the addition to get reading glasses instead of distance glasses.
If there is only one ADD power on your prescription for bifocals, this means that the same ADD power is used for both eyes. If there is no ADD power given, leave this section blank when ordering.
A Prism correction is used to treat muscular imbalance or other conditions, and the numbers are usually left blank on the prescription. Sometimes, if the basic prescription is followed by a small number with a superscript (1^) it indicates prism correction. There may be more than one set of prism numbers for each eye.
Note on entering your prescription info: It’s very important to pay close attention to the plus and minus sign, as this will greatly affect the lens. If there is anything on the prescription you are not familiar with, please call our Customer Service and we will be happy to assist you.
Also very important: When choosing frames for bifocal or progressive lenses, you must have a lens height of at least 28mm. It is for this reason that our site blocks sizes smaller than 28mm so you can’t make a mistake.
Here is some more detail on prescriptions…
On a typical prescription, you will see two sets of rows. Most of the time top portion is for your OD or right eye while the bottom portion is for your OS or left eye.
For Distance Correction, there should always be a value under Sphere and most of the time it is negative. Its abbreviation is ‘D.V.’ which stands for Distance Vision.
For Reading-only correction, there should always be a value under Sphere and most of the time it is positive. If there is 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 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. Some doctors use positive (+) cylinder and some use negative (-), there is a big difference between the two so please pay close attention to the positive and negative signs. If you don’t have astigmatism correction, doctors might just leave it blank or simply SPH or DS, which means Sphere or Diopters Sphere. Axis should be from 1-180 degrees, if you see a value like ‘5’ under axis, this is also the same as ‘005’ or ‘5 degrees’. It should always be a whole number and there should no be decimal point on the axis.
What is the PD (Pupillary Distance)?
PD, or pupillary distance, is the distance from the center of the pupil (the black spot in the eye) of one eye to the other. This measurement refines the positioning of your lenses within the frame you have chosen.
This measurement is necessary to ensure the correct positioning of your lenses within the frame you have chosen. Your optician or doctor can provide it in minutes, and so we recommend that you ask for it when you have your vision checked. Or you may ask someone to measure it for you but advise them to be at about an arm’s length away from you.
You can also have a friend measure or measure by yourself by facing a mirror. For single vision lenses, you may choose to use an average PD of 63mm, but for Bifocal or Progressive lenses, we still strongly recommend to get this information from your optician.
For your information, most adults’ PD are between 55-65mm and most kids’ PD’s are between 42-54.
Why isn't the PD (Pupillary Distance) on my prescription?
The PD is part of the fitting process. Many doctors do not put it on your prescription because they assume you will come back to them to get the glasses or else you will get the measurement done wherever you buy them. They do measure it and you can call them and ask them.
If you are getting SINGLE VISION glasses (for distance or reading) then you can measure it yourself (see below). If you are getting MULTI-FOCAL glasses (for bifocal or progressives, you should CALL YOU DOCTOR and get the correct PD as it can really make a difference with these types of glasses.
Why do I have 2 numbers for my pupillary distance measurement?
Sometimes the PD is measured from one pupil to the other and sometimes it is measured from the center of your nose to each pupil. If you have 2 numbers, you can add them together and you will get a numbers somewhere in the sixties (millimeters).
Sometimes you will have a Distance Vision PD (e.g. 64mm) and a Near Vision PD on the same prescription. You can use the Distance (usually the larger one) unless there is more than a 5mm distance in which case you average – take the middle. Example: D=67 / N=61 use 64mm.