You go to your optometrist or ophthalmologist and they test your eyesight. Unless you have perfect vision, they hand you a slip of paper (or send an electronic file) that has all these numbers and words that probably mean nothing to you. But they’re your eyes, and you want to know what your prescription means.
I’m going to break down each aspect of your eye prescription, so you can fully understand what’s going on with your sight.
OD, OS, and OU
One of the first things you’ll probably notice are the rows starting with either OD or OS (and sometimes OU). These codes are much simpler than you might realize.
- OD stands for oculus dexter, which means your right eye
- OS stands for oculus sinster, which means your left eye
Occasionally, you could see an OU.
- OU stands for oculus uterque, which means both eyes
Normally the first column will be an “S,” a “SPH,” or “Sphere.” This is the amount of nearsightedness or farsightedness you have.
A zero (0) would be no correction. So the farther away you get from zero, the more correction you need. These numbers describe how many diopters (the measurement of lens power) that you need to have perfect vision.
To determine what direction that correction should go (either to help you with seeing far away or seeing up close), there will be a plus or minus:
- When the sphere number is by a plus sign (+), you are farsighted
- When the sphere number is by a minus sign (-), you are nearsighted
Here are two examples: If your prescription reads +1.25, you are slightly farsighted. If your prescription reads -5, you are significantly nearsighted.
The next column may be a “C” or “Cylinder,” and it’s used to describe astigmatism, which just means your eye isn’t perfectly round (like most people!).
Some people’s astigmatism is bad enough that it needs lens adjustments to fix it. Just like with a sphere, a number is given and a plus or minus sign. The bigger the number, the worse your astigmatism.
The “Axis” is also related to astigmatism. Where the cylinder describes how much astigmatism you have, the axis tells you where it is located.
You will find a number somewhere between 0 and 180. This ensures the astigmatism lens fix is placed at the perfect spot on your glasses.
The “Add” is all about magnifying power if you are getting multifocal lenses (commonly bifocals, but sometimes trifocals). This is always a “plus” for farsighted, but you will rarely see an actual plus sign (+) noted.
This number will almost always be the same in both eyes and range somewhere between 0.75 and 3.00.
Very few eye prescriptions will have this next part, but it’s good to know about in case it’s on yours. The “Prism” is there for those with eye alignment issues only.
There will be a number as well as a direction like “base up” or “base down” – this just describes where the thicker edge of the prism lens will go.
Reading Your Eye Prescription
Now you should be able to make sense of your eye prescription. Make sure you visit your eye care specialist regularly to see if any numbers need to be changed.
And don’t forget that vision is not the only reason for primary eye care – it’s important to have a full set of tests done to check for eye diseases (and even other diseases like heart disease and stroke!) regularly.