Getting an eyeglass prescription can be confusing if you don’t understand the numbers and abbreviations. OD, OS, SPH, CYL—what do they mean? This guide will break it all down so you can read your prescription and choose the best glasses for your needs.

1. What Do the Abbreviations Mean?

Your prescription includes terms that specify your vision correction needs:

• OD (Oculus Dexter): Right eye

• OS (Oculus Sinister): Left eye

• OU (Oculus Uterque): Both eyes

• SPH (Sphere): The power of your prescription (+ for farsightedness, - for nearsightedness)

• CYL (Cylinder): Correction for astigmatism

• AXIS: A number (0–180°) that indicates astigmatism orientation

• ADD: Additional power for reading or bifocal lenses (common for presbyopia)

• PD (Pupillary Distance): The distance between your pupils, ensuring proper lens alignment

2. Common Prescription Types

✔ Single Vision: Corrects one type of vision, for nearsightedness, farsightedness, or astigmatism.
✔ Bifocals/Progressives: Corrects two or more distances of vision, usually for far and near up. Includes additional magnification for reading (ADD value).

3. Why Understanding Your Prescription Matters

• Choosing the Right Lenses: Knowing your SPH, CYL, and ADD helps select single vision, bifocal, or progressive lenses.

• Buying Online: Many online retailers require you to input your prescription manually.

• Pupillary Distance (PD): Essential for proper lens alignment—sometimes not included on the prescription, so you may need to measure it.

4. Can You Use Your Eyeglass Prescription for Contact Lenses?

No, a contact lens prescription includes additional details like base curve (BC) and diameter (DIA), which are not found on eyeglass prescriptions. Always get a separate contact lens exam.

Conclusion

Understanding your eyeglass prescription empowers you to make informed decisions when purchasing glasses. Whether you buy from an optician or online, knowing what OD, OS, SPH, and CYL mean ensures you get the best fit for clear and comfortable vision.