You may understandably think that your prescription will be the same regardless of whether you plan to wear glasses or contact lenses. But, in fact, they’re different. That’s because eyeglasses rest on your nose, a few millimeters away from your eyes, while contact lenses sit directly on them.

Your contact lens prescription may also change based on the brand and type of lens you and your eye doctor decide on. Different manufacturers make lenses differently. So, your eye doctor may need to adjust your prescription slightly.

That’s why your doctor will also note the type of lens you wear, such as Acuvue Oasys, Clariti 1day, or Alcon Total30, to name a few. 

If you plan to wear contacts instead of glasses, tell your eye doctor before your exam. That way, they can capture all the measurements needed for contact lenses specifically.

Here are a few other measurements you’ll find on your contact lens prescription.
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BC or BASE CURVE

This indicates the curvature of your contact lens. It helps ensure the lenses fit closely to the surface of your eye for better vision and comfort. Measured in millimeters, it is always a value between 8 and 10. 
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DIA or DIAMETER

This measures the distance across your contact lens. Measured in millimeters, it is usually between 13 and 15.
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ADD or ADD POWER

This means to add magnification for bifocal, trifocal, or progressive contact lenses. However, instead of a number as you’d seen on a glasses prescription, your eye doctor will note low, medium, or high in the Add Power column for contact lenses.
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EXPIRES

All prescriptions have an expiration date. For contact lenses, the expiration date is one year from the date of your eye exam. It could be shorter if your prescription changes rapidly or you have a health condition that can affect your vision. In that case, your eye doctor may set a shorter expiration date so that you return for evaluation sooner.