If you are having trouble navigating your eyewear prescription, you are not alone. The good news is that it is not that difficult once you make sense of several key terms and abbreviations. Let’s explore these together:

OD vs. OS: What Do They Mean?

OD and OS are Latin abbreviations that ophthalmologists and optometrists use to distinguish between eyewear prescriptions for the right and left eye.

  • OD (Oculus Dexter) refers to the right eye.
  • OS (Oculus Sinister) refers to the left eye.

You may also stumble upon the abbreviation OU (Oculus Uterque), which refers to both eyes together.

Other Abbreviations to Know

  • Sphere (SPH) indicates the lens power prescribed to correct nearsightedness or farsightedness. SPH is measured in diopters (D).
  • Cylinder (CYL) represents the additional lens power required to correct astigmatism. CYL is also measured in diopters (D).
  • Axis is the orientation of the CYL power in degrees, ranging from 0 to 180.
  • ADD (Reading Addition) represents the additional magnifying power required for close-up vision, typically used for bifocals or reading glasses.
  • Prism indicates the amount of prismatic power necessary to correct eye alignment issues like double vision. Prism is measured in prism diopters.

How to Understand the Numbers

Most abbreviations on your eyewear prescription will be followed by numbers. These numbers indicate how much correction your vision needs; they will be negative when correcting nearsightedness and positive when correcting farsightedness.

For instance, if your prescription reads +3.00, your eyeglasses need 3 diopters of strength to correct farsightedness. If your prescription reads -1.50, that means that your glasses require 1.5 diopters of strength to correct nearsightedness. The higher the number, whether accompanied by a + or – sign, the more correction is needed.

Prescription for Contact Lenses

Contact lens prescriptions differ from eyeglasses prescriptions in several ways:

  • Contact lens prescriptions are measured in millimetres for the base curve and diameter of the lens rather than diopters.
  • Contact lens prescriptions often combine SPH, CYL, and Axis values into a single power known as the spherical equivalent.
  • ADD may be already included in contact lens prescriptions, while glasses prescriptions specify a separate reading prescription for bifocals.

The Importance of Regular Check-Ups

Once you decipher your eyewear prescription, know that it will likely change several times over your lifetime. Regular check-ups will help you to keep your prescription and eyewear up-to-date, keeping your eyes healthy and comfortable. Contact Laurier Optical today to book your examination.