How To Measure the Base Curve of Your Contact Lens

Inserting a contact lens

The measurement of the base curve of a contact lens is also known as BCR or base curve radius or the posterior apical radius. This measurement is taken so that the contact lens will fit the cornea of the one wearing it. The right measurement of the base curve is needed so that the person wearing it will be comfortable and will feel as though nothing is worn on the eyeball. The base curve is the measurement of the back surface of the base contact lens.

Improper fitting of base wear contact lenses can make your eyes irritated. This can lead to inflammation of the eyeball, swelling, or the eyeball can even have abrasions. These cases can lead to eye infection and can further decrease your ability to see clearly.

Here are some tips on how to measure the base curve of your contact lens:

  • Measurement. The base curve measurement of the contact lens is done in millimeters. This measurement must approximately match the radius of your cornea so that it will fit your eye. Usually, the values of the base lens curve of contact lenses range from 8 mm. up to 10 mm.
  • How base curve is measured. The base curve of the contact lens is measured when you go to the optometrist. The doctor does this so that you can have the proper lens fitting. He will give you a prescription so that you can have a soft contact lens made with the right size.
  • Lens clock. The lens clock is a device that is used to measure the base mirror curve of the contact lens. This lens clock is used by the optometrist in order to know the curvature of the cornea. The lens clock is made of three probes that will have contact on the lens. A mathematical formula is then used to be able to determine the base curve of the contact lens.
  • Transducer. A transducer can also be used to measure the base curve of a contact lens. It is a device that is primarily used to obtain the lens height or thickness, but it can also be used to measure the base curve. Transducers from Olympus are the ones that are most commonly used commercially. Some of the best models are the Model 25 Multi Plus, the Model 35 or the Model 35DL.

It is best to have your base curve measured by an optometrist once every few months so that your contact lens can be updated. The prescription for your contact lens is just like a prescription for medicines.

Once you get your base curve measured, you can choose base colors for your soft contact lens. You can also have clear contact lenses. Make sure to have eye drops with you when you are wearing contact lenses so that you won’t have dry eyes. Also, remove your contact lenses and let your eyes rest during the nighttime when you are asleep. When you are in the house, you can just wear eyeglasses so that you will still be able to see without your contact lenses.  


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