How to Read Your Eyeglass or Contact Lens Prescription

July 18, 2020
A doctor showing a patient a screen that displays a lens.


When you look at your eyeglass or contact prescription, you will see a bunch of numbers and letters listed but you may not really know what they mean. In fact, you may even know which power is for which eye, but you still don’t know why. We’re here to educate you on how to interpret your eyeglass or contact lens prescription.

What do OD and OS Mean?

The first part of getting what your eyeglass prescription means is determining what “OD” and OS” mean. They abbreviate the words oculus dexter and oculus sinister: Latin words for “right eye” and “left eye.” You may also see a column labeled “OU,” and this abbreviates the Latin term oculus uterque. This means “both eyes.”

Nowadays, you will just see the abbreviations RE (right eye) and LE (left eye) rather than the more confusing OD and OS. On your eyeglasses prescription, the information for your right eye (OD) comes before the information for your left eye (OS). This is because eye doctors see your right eye on their left (first) and your left eye on their right (second).

Your eyeglass prescription will also contain others terms and abbreviations such as:

Sphere (SPH): The amount of lens power, measured in diopters (D), which corrects nearsightedness or farsightedness. If the number under this heading features a minus sign (–), this means you’re nearsighted; if it has a plus sign (+), this means you’re farsighted.

Cylinder (CYL): The amount of lens power for astigmatism. The number in this column may be preceded with a minus sign or a plus sign (for farsighted astigmatism).

Axis: This is the lens meridian with no cylinder power, meant to fix astigmatism, represented by a number between 1 and 180. The number 90 shows the vertical meridian of the eye, and the number 180 shows the horizontal meridian.

Add. This is the additional magnifying power that applies to the bottom portion of multifocal lenses to fix presbyopia. It ranges from +0.75 to +3.00 D and is the same for both eyes.

Prism. This is the amount of prismatic power, measured in prism diopters that compensates for eye alignment problems.

Contact Lenses

You will need a separate contact lens prescription if you want to wear contacts. Contact lens and eye glasses prescriptions are not interchangeable.

  • Power, PWR, Sphere or SPH: Usually listed first after OD, OS, or OU, indicating the strength of correction needed for that particular eye.
  • Base Curve or BC: Indicates how curved the inside of your lens is, usually ranging from eight to 10.
  • Diameter or DIA: The width of the contact lens from edge to edge, measured by millimeters.
  • Brand: This is the name of the specific contact lens brand or type you’ve been prescribed.

Contact Simon Eye

Still have questions? We can help. Contact us at 302-239-1933.

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