To read an eye prescription, you need to understand the common abbreviations and numbers that describe your vision correction needs:
Key Components of an Eye Prescription
- OD and OS : These indicate which eye the prescription refers to.
- OD (oculus dexter) = right eye
- OS (oculus sinister) = left eye
- OU means both eyes
- SPH (Sphere) : This number shows the lens power needed to correct nearsightedness or farsightedness, measured in diopters.
- A minus (–) sign means you are nearsighted (difficulty seeing far away).
- A plus (+) sign means you are farsighted (difficulty seeing close up).
- The higher the absolute number, the stronger the prescription
- CYL (Cylinder) : This indicates the amount of lens power needed to correct astigmatism, which is caused by an irregularly shaped cornea.
- If this box is empty, it means no astigmatism correction is needed.
- A higher number means more astigmatism correction
- AXIS : This number (from 1 to 180 degrees) shows the orientation of the astigmatism correction. It tells the optician where to position the cylindrical power in the lens. It does not indicate strength, just direction
- PRISM and BASE : These are less common and relate to prism correction for eye alignment issues. Prism helps with double vision or eye coordination problems. The BASE indicates the direction of the prism
- PD (Pupillary Distance) : This measures the distance between your pupils in millimeters, ensuring the lenses align correctly with your eyes. It may be listed as a single number or two numbers (for each eye)
Additional Notes
- Contact lens prescriptions include additional parameters like base curve and diameter because lenses sit directly on the eye, unlike glasses
- Prescriptions usually expire after about two years, so regular eye exams are recommended
In summary, to read your eye prescription:
- Identify OD and OS for right and left eyes.
- Look at SPH to see if you are nearsighted (–) or farsighted (+) and the strength.
- Check CYL and AXIS if you have astigmatism.
- Note PD for proper lens alignment.
- Understand any prism correction if present.
This will help you understand what lenses you need for clear vision
