Pull out your eyeglass prescription and it can look like a secret code: rows of abbreviations and plus or minus numbers. The good news is that every part has a simple meaning. Here is what each one tells you about your vision.
OD and OS (and OU)
These come from Latin. OD (oculus dexter) is your right eye, and OS (oculus sinister) is your left eye. If you see OU (oculus uterque), that refers to both eyes together. Your prescription lists a separate set of numbers for each eye because they rarely need exactly the same correction.
SPH (Sphere)
Sphere is the main strength of the lens, measured in units called diopters. A minus sign (for example, -2.00) means you are nearsighted and need help seeing things far away. A plus sign (for example, +1.50) means you are farsighted and need help with close-up vision. The bigger the number, the stronger the correction.
CYL (Cylinder) and AXIS
These two go together and describe astigmatism, where the eye is shaped a little more like a football than a basketball. CYL is the amount of astigmatism correction, and AXIS (a number from 1 to 180) tells the lab the angle where that correction is placed. If both are blank, you simply do not have astigmatism, which is perfectly normal.
ADD
ADD is extra magnifying power added to the bottom of the lens for reading. You will usually see it if you wear bifocals or progressives. It is always a plus number and is often the same for both eyes.
PD (Pupillary Distance)
PD is the distance between the centers of your pupils, measured in millimeters. It is not always printed on the prescription, but it matters: it lets us center each lens exactly in front of your eye so your glasses are comfortable and sharp. If you are ordering, we can measure it for you.
Prism and Base
Most prescriptions do not include these. When they do, prism corrects how the eyes work together (it can help with double vision), and base is the direction the prism points. If your prescription has these, it is worth talking through with your optician.
The bottom line
You do not need to memorize any of this. Bring your prescription to us and we will translate it, recommend the right lenses, and make sure everything is centered correctly. A current prescription is usually valid for one to two years, so if yours is older than that, an updated exam is a good first step.