How to Read Eyeglasses Prescription
Understanding your prescription is key to ensuring your lenses correct your vision accurately. This guide breaks down the components of a typical prescription to help you decode it like a pro.
1. OD and OS: Which Eye Is Which?
Eyeglass prescriptions use Latin abbreviations to denote eyes:
- OD (Oculus Dexter): Your right eye.
- OS (Oculus Sinister): Your left eye.
Some prescriptions may use OU (Oculus Uterque), meaning "both eyes," if the correction is identical.
2. Sphere (SPH): Correcting Nearsightedness or Farsightedness
The Sphere (SPH) value indicates the lens power needed to correct your vision:
- Negative numbers (-): Nearsightedness (difficulty seeing distant objects).
- Positive numbers (+): Farsightedness (difficulty seeing close objects).
For example, a "-3.50" SPH means you need correction for moderate nearsightedness.
3. Cylinder (CYL) and Axis: Addressing Astigmatism
If you have astigmatism (an irregularly shaped cornea or lens), your prescription will include:
- Cylinder (CYL): The power needed to correct astigmatism. This can be positive or negative (e.g., -1.25).
- Axis: A number between 1 and 180 indicating the orientation of the astigmatism correction. For instance, "Axis 90" means the correction aligns vertically.
4. Pupillary Distance (PD): Ensuring Proper Lens Alignment
Pupillary Distance (PD) measures the distance (in millimeters) between your pupils. This ensures lenses are centered correctly. PD values typically range from 54–74 mm. Many prescriptions omit this, so ask your optometrist to include it if you’re ordering glasses online.
5. Add Power (ADD): For Multifocal Lenses
If you need bifocals or progressive lenses, Add Power (ADD) indicates the magnification for close-up tasks (e.g., reading). This number is always positive (e.g., +2.00) and is the same for both eyes.
6. Prism and Base: Rare but Important
A small percentage of prescriptions include prism correction to address double vision or eye alignment issues. This will list:
- Prism Power: Measured in prism diopters (e.g., 1.5△).
- Base Direction: The direction the prism is oriented (e.g., "Base In" or "Base Up").
Eyeglasses Prescription Chart Example
A prescription written for someone with nearsightedness.
A prescription written for someone with farsightedness and astigmatism.
Progressive prescriptions (multifocal)
Prescriptions with prism correction
Reminders
● Your eyeglasses prescription is also eligible to use for sunglasses, but not for contact lenses.
● Expiration Date: Your eye prescription probably won’t be the same forever—it’s important to have your eyes examined regularly to make sure they’re seeing as best as they possibly can. Eye prescriptions are normally valid for a year or two before they expire (the exact time period can vary depending on state laws). After that, you’ll need to renew it by scheduling an eye exam.
● If you have any problems reading your prescription, please contact our customer service and we will help you purchase your favorite new glasses!