Eye exams may seem simple: you visit the doctor, get your vision tested, and walk out with a prescription. But for many patients, understanding your eye prescription can feel like decoding a foreign language. What do all those numbers and abbreviations actually mean?
Let’s break it down so you can better understand your vision and make more informed choices about glasses or contact lenses.
What Does 20/20 Vision Mean?
Most people know that 20/20 vision is considered “perfect” eyesight. It means you can see clearly from 20 feet away—what a person with normal vision should be able to see at that same distance.
If your vision is 20/40, for example, it means you need to be 20 feet away to see what someone with normal vision sees from 40 feet away. The higher the second number, the worse the eyesight.
Common Terms on Your Eye Prescription
Here are the most common elements you’ll see on your eyeglass or contact lens prescription:
OD and OS
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OD (oculus dexter) = Right eye
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OS (oculus sinister) = Left eye
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Some doctors use RE and LE instead for clarity.
Sphere (SPH)
This indicates the strength of your lens prescription.
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A minus sign (-) means you’re nearsighted (can see up close but not far).
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A plus sign (+) means you’re farsighted (can see far away but struggle with close-up vision).
Cylinder (CYL) and Axis
These numbers relate to astigmatism, a common condition where the eye isn’t perfectly round, causing blurred vision.
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CYL shows how much correction is needed.
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Axis shows the orientation of the astigmatism in degrees (between 1 and 180).
You’ll only see CYL and Axis if you have astigmatism.
Add
This is the added magnification used for bifocals or multifocal lenses, helping with close-up tasks like reading.
Prism
Prism correction is used to address eye alignment issues. It helps reduce double vision by properly aligning how your eyes work together.
Need Help Understanding Your Eye Prescription
Your eye prescription is a custom blueprint for your vision needs. Understanding the meaning behind each value—especially SPH, CYL, and ADD—can help you take better control of your eye health. If you ever have questions, don’t hesitate to ask your eye doctor or optical provider for clarification.
Eye exams may seem simple: you visit the doctor, get your vision tested, and walk out with a prescription. But for many patients, understanding your eye prescription can feel like decoding a foreign language. What do all those numbers and abbreviations actually mean?
Let’s break it down so you can better understand your vision and make more informed choices about glasses or contact lenses.