Example of eyeglass prescription

If you’ve been wearing glasses for a while, you’ve probably heard your eye doctor make a reference to your eyeglass prescription. If you wear contacts, you might have also noticed the numbers on the sides of your contact lens box. Those numbers are a huge part of your eye care experience and can indicate the next steps towards fixing your vision.

What are the different prescription abbreviations?

Your doctor may write down your prescription on a card featuring a variety of letters. Each of these letter sets have their own meaning:

Specific eye

  • OD: Oculus dexter (right eye)
  • OS: Oculus sinister (left eye)
  • OU: Oculus uterque (both eyes)

Lens power

  • PWR or SPH: Power or sphere

Lens curvature and diameter

  • BC: Base curve
  • DIA: Diameter

What are the different numbers?

Now that you know what each of the abbreviations represents, you can begin to look at the numbers in each of the categories.

Power or sphere

This number represents the lens power needed to correct your vision, written in increments of 0.25. Positive numbers indicate farsightedness, while negative numbers indicate nearsightedness.

Axis and cylinder

For patients with astigmatism, they will have additional numbers to indicate the direction of the condition (axis) and lens power (cylinder) to correct it. The axis is measured in degrees between 1ᵒ to 180ᵒ, while the cylinder is measured in increments of 0.25.

Base curve and diameter

Your contacts are not a “one size fits all” as the curvature and diameter of your lenses are determined for the most comfortable fit. Your base curve, or BC, is measured in millimeters and ranges between 8.0 to 10.0. Your diameter is also measured in millimeters and typically ranges between 13.0 to 15.0.


For those ages forty and up who require bifocals or reading glasses, this extra category signifies extra magnifying power. Like power and cylinder, this too is measured in increments of 0.25.

How do I update my eyeglass prescription?

Over time, your prescription for your glasses or contact lenses will need to be updated to ensure that your vision is as accurate as possible. At CEENTA, our ophthalmologists and optometrists can examine your eyes to find the right lenses for you. Schedule your next prescription update with CEENTA today to enjoy the sights around you again. 

This blog is for informational purposes only. For specific medical questions, please consult your doctor. New patients can make appointments online with our eye doctors in North and South Carolina. Current patients can also make appointments through myCEENTAchart with physicians they have already seen.


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