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How to Select the Right Base Curve (BC)

May 05,2022 | Lensweets

The base curve of colored contact lenses is one of the important factors in ensuring wearing comfort. Wearing lenses with the correct base curve helps them stay firm and float on the cornea's surface. Wearing an inappropriate base curve, either loose or too tight to bear.

The base curve does not determine the size of the colored contact lenses. The base curve determines the curve, and the diameter (DIA) determines the size. If the base curve is too large, the lenses will slide and move. If the base curve is too small, it is difficult to tolerate contact. Your eyes can become dry because they affect oxygen flow and tear exchange.

What is Base Curve?

Base curve (BC) is a measurement of the curve of the interior side of contact lenses. If we imagine a contact lens fitting perfectly on an imaginary sphere, the base curve is calculated as the radius of that sphere. As a result, the higher the base curve value, the flatter the lens will be, as the imaginary sphere is larger.


Why is Base Curve Important?

The BC of your colored contact lenses will determine how tight of a fit your contacts have, which will, in turn, affect how comfortable they feel to wear depending on your cornea’s shape, as well as how effectively oxygen transmission and tear exchange can occur while wearing them.


This comes into play, particularly for people who haven’t been prescribed lenses by an eye doctor and therefore don’t know their ideal BC. Colored contacts can be non-prescription, but the BC of each pair will usually be standardized and may not align with what is best for your eyes. Aside from causing discomfort, badly fitting contacts can place unnecessary strain on your eyes and cause headaches and vision problems. In order to avoid this, it’s important to make sure your contacts fit properly, and one key to this is figuring out your ideal BC.

How to Know if Your Lenses Have the Right BC

The vast majority of people will find themselves perfectly comfortable wearing lenses with a BC between 8.4 and 8.8 mm, a range that most Lensweets contacts fall into. However, here are some things to look out for that may indicate that you need a different BC:

Too loose/Need lower BC

  • The lens is excessively off-center
  • Excessive post-blink lens movement
  • Lens displacement from the cornea
  • Lens folding or falling out
  • Corneal staining
  • Discomfort

Too tight/Need higher BC

  • The lens is excessively off-center
  • Little to no lens movement
  • Redness (hyperemia)
  • Inflammation
  • Corneal staining (more severe than if too loose)
  • Discomfort

If you experience any of these symptoms, try a pair of tighter or looser lenses, depending on what you think you need. Alternatively, you can consult an eye doctor to figure out the problem or find your ideal BC. Please consult all Lensweets product descriptions to ensure that you purchase color contacts that are suitable for your eyes.