How to Read an Eye Prescription

Looking at an eye prescription can feel like reading a foreign language. However, decoding the grid of numbers is straightforward once you understand the core clinical abbreviations.

OD vs. OS (The Eyes)

  • OD (Oculus Dexter): Your Right Eye.
  • OS (Oculus Sinister): Your Left Eye.
  • OU (Oculus Uterque): Both Eyes.

The Power Values (Measured in Diopters)

1. SPH (Sphere)

This indicates the primary lens power. A minus sign (e.g., -2.00) means you are nearsighted (myopic). A plus sign (e.g., +1.50) means you are farsighted (hyperopic).

2. CYL (Cylinder)

This indicates the amount of lens power needed for astigmatism. If this box is blank, you have little to no astigmatism.

3. AXIS

If you have a CYL value, you MUST have an Axis. This is a number between 1 and 180 that tells the lab exactly where to align the astigmatism correction on the lens.

4. ADD (Addition)

The added magnifying power applied to the bottom of progressive lenses or reading glasses. Want to know what your ADD means? Try our Reading Power Calculator.

Medical Disclaimer

This article is provided for educational and informational purposes only. CorrectLens does not provide medical diagnosis, treatment, or prescription services.

Online vision tests measure visual acuity (clarity of sight) and basic visual performance. They cannot detect eye diseases such as glaucoma, cataracts, macular degeneration, retinal disorders, or neurological conditions.

A comprehensive eye examination performed by a licensed eye care professional is required for medical diagnosis and prescription accuracy.

Medical References