How do I know my eyeglass prescription?

Deciphering Your Eyeglass Prescription: A Simple Guide

So you’ve just had an eye exam, and you’re handed a slip with numbers and abbreviations. This is your eyeglass prescription, a critical piece of information for your optical needs. But how do you decipher it? Let’s demystify the elements of an eyeglass prescription.

eyeglass prescription

1. Understanding the Basics

An eyeglass prescription contains specific terms and numbers indicating the correction needed for each eye. This correction addresses refractive errors that blur vision, such as myopia (nearsightedness) or hyperopia (farsightedness).

2. Key Terms on Your Eyeglass Prescription

  • OD & OS: These abbreviations stand for “Oculus Dexter” (right eye) and “Oculus Sinister” (left eye), respectively. If you see “OU,” it means “Oculus Uterque” or both eyes.
  • SPH (Sphere): Indicates the lens power required to correct nearsightedness or farsightedness. A negative value (-) suggests myopia, while a positive value (+) indicates hyperopia.
  • CYL (Cylinder): This number, if present, pertains to astigmatism, a condition where the eye isn’t perfectly round, causing distorted vision.
  • AXIS: Accompanying the CYL value on your eyeglass prescription, AXIS indicates the orientation of astigmatism, ranging between 0 and 180 degrees.
  • ADD: This is relevant for bifocal or multifocal lenses, showing the magnifying power for reading or close-up work.
  • PD (Pupillary Distance): Represents the distance (in millimeters) between the centers of your pupils. It’s essential for aligning the lenses properly in front of your eyes.

3. How to Read Your Eyeglass Prescription

Typically, the layout will resemble a chart with columns for OD, OS, SPH, CYL, AXIS, and possibly ADD. The corresponding numbers in each column inform lens makers about the necessary adjustments for each eye.

4. Prescription Expiry

Remember, prescriptions usually have an expiration date, often one to two years from the exam date. Regular check-ups ensure your prescription remains up-to-date.


Understanding your eyeglass prescription is empowering. While you may not craft the lenses yourself, knowing what each term signifies ensures you’re informed when choosing glasses. When in doubt, always consult with your optometrist for clarity.


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