How to read your prescription (Rx)

January 27, 2016

So, you came to Umizato and found a fantastic pair of glasses -- like our beautiful Bagan in tortoise or our ultra-lightweight Orion in red, and now you need to get a new prescription or enter one that is current. If you are about to go out and find an ECP (Eye Care Professional) to provide you with a new Rx, then please make sure to know your rights and also remember to ask for your PD (pupillary distance)! Of course, if you don't have your PD, you can always use our handy PD measure tool online.

If, on the other hand, you have your Rx in your eager hands, then the following will help you in deciphering the codex that is your eyeglass prescription. Keep in mind, there are no standard formats for the prescription, but, generally, they all provide the core set of information in a similar fashion.

In all prescriptions, here is the minimum information you will find:

  1. Patient name
  2. Date of the exam
  3. Expiration date of Rx (normally at least one year)
  4. Patient contact information
  5. Right eye (OD) and left eye (OS) sphere power in diopters with a negative or positive sign
  6. OD and OS cylinder and axis if needed -- if you have a cylinder then you must have and axis designation

Not all ECPs will want to provide a PD if you are not purchasing the eyewear from them, but some states require that they give it to you anyways.

Let's take a look at a couple of examples of what the prescription can look like.

glasses prescription example

 All prescriptions choose to designate the right eye and left differently. Some write it very simply (as this one does) and many tend to use the medical abbreviations for the right eye (OD or oculus dexter) and left eye (OS or oculus sinister), and then some use both. There are also some prescriptions that have OU or oculi uterque meaning both eyes.

The Rx above uses the plain and simple strategy for "Right" and "Left" eyes. The first column after each eye is the "Sphere" column. This sphere is the power of the lens needed to correct the refraction error for each eye. If this number is negative, you are myopic (nearsighted or you are able to see near easier). If this number is positive then you are hyperopic (farsighted or you are able to see far away easier).

The second column is the "Cylinder" column. This column is only filled in if you have astigmatism and if this column has a number, then the corresponding "Axis" column should be filled in, too. You may have astigmatism in one eye, in both, or in neither eyes. In this example, "Sphere" is designated for the right eye and this is just the doctor's way of saying there is no correction needed. The left eye in this example has a cylinder and an axis. The cylinder will be in diopters (similar to sphere) and the axis will be a number between 1 and 180.

In this example, there is an entry for "type" which is "SVL." This means that this is for single vision lenses as opposed to a prescription for bifocals or progressives which would then need a add power. Also, you will notice that this prescription doesn't even have columns for prism and diopters. We will discuss this in the next example.

eyeglass prescription example

Notice the differences in this second Rx example. Let's start with the labels for the right eye and left eye are replaced with the medical terminology of OD and OS respectively.

In the sphere column, the powers are both negative, which is far more common than the previous example which had a negative power for one eye and a positive power for the other eye (quite rare). The doctor also chose not to write the decimal in the numbers for the sphere powers which is common. The right eye (OD) would be read as -4.50 and OS would be -4.25. The decimal is left out as a sort of a shorthand. It's obvious to the optician that this is not -450 power as there are no lenses of such power -- the patient would need a cart to carry such glasses! 

In this second example, the cylinder for the right eye is left blank to denote that there is no correction necessary.

Unlike the previous example, this prescription has "PRISM" and "BASE" columns. These are provided for correction of only a small percentage of patients and is normally not used.

This example is particularly unique from the first in that it provides an "ADD" column. The add number is measured in diopters and is used to correct for near vision, normally for reading. If you need bifocals or progressives, it would be necessary to have these values -- although in most cases these numbers will be the same and some prescriptions will write a single number to show the add power for both eyes.

Our last example shows a couple differences from the other prescriptions. The first difference is how the OD and OS columns are grouped with the labels "D.V." and "N.V." respectively. DV is for distance vision and NV is for near vision. If this patient needed reading glasses, then the NV rows would be most likely filled with only values in the "SPHERICAL" column to denote the dioptic power for each eye.

Something else you will notice in this third example, is the "DS" written in the "CYLINDRICAL" columns. This is just means there is no astigmatism present and cylinder powers are not necessary for correction (DS is short for diopters sphere). Doctors may also write "SPH," or "Plano," or even "00," which all mean pretty much the same thing -- that there is no astigmatism for that particular eye and no correction is needed.

Wow, so just from 3 examples you can see how much prescriptions can differ in how the doctor wishes to designate the values. There are many more and if you are still having problems reading your Rx, please don't hesitate to message/chat with us via Facebook Messenger, send us a question via our contact page, or call us.


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