What Does Base Curve or “BC” for Contact Lenses Mean?

When it comes to wearing contact lenses, comfort and fit are key factors to ensure optimal vision and eye health. One crucial aspect that dictates these factors is the ‘base curve’, often abbreviated as BC. Though most contact lenses come in specific base curve options when your doctor prescribes them to you, it’s important to know the role that base curve can play in the comfort and effectiveness of your contact lenses.

Base Curve (BC) Meaning

The Base Curve of a contact lens is the measurement of the back curvature of the contact lens, the “fitting curve”. Base Curve is the term that is used to describe the caliber of steepness of the lens needed for properly matching the shape of the person’s cornea of their eye.

• When a person has a more rounded shape of their cornea, they need a steeper lens to fit their cornea. 
• When a person has a less rounded shape of their cornea, they need a flatter fitting contact lens.

When you receive a prescription for your contact lenses, it must at the very least include these three criteria:

1. Lens Power
2. Diameter (DIA)
3. Base Curve (BC)

The base curve is an important part of your contact lens prescription, and your prescription will be deemed “invalid” without it.

The back curve has to be determined to appropriately fit the front curve of the cornea (the clear dome over the color part of the eye) so that the contact lens fits comfortably.

Base Curve Explained (Video)

Range of Base Curve Values

Base curve numbers are measured in millimeters (mm). Contact lens manufacturers will provide one or more options for the different BC sizes that their lenses will come in.

The normal range for soft disposable contact lenses is from 8.3mm through 9.0mm, with 8.6mm being the average base curve. 

Here is a way to visualize what the base curve actually is:

How to Select a Base Curve For Your Contact Prescription

You’ll find out what your specific base curve is during an eye exam with a doctor.

Your base curve is determined by your doctor by using an instrument called a keratometer. The keratometer measures the shape (steepness) of your cornea. 

Once the doctor understands the steepness of your cornea and combines that information with other details learned during the eye exam, then they can choose a contact lens that is made in a base curve most suited to your eye. 

Not all contact lens designs have the same base curves, so don’t expect your base curve to remain the same if you switch to a different design of contacts. You can still find a contact lens that fits perfectly comfortably within a certain range of the exact base curve of your eye.

Your doctor must choose the best option available based on that specific design of contact lens base curve availability.

Risk of Using Contacts with the Wrong Base Curve

If your contact base curve number is not right, then our eyes may be less comfortable or even experience damage over time. Permanent damage from an incorrect base curve would take prolonged use of these contacts, so don’t worry too much. But be sure to talk to your eye doctor if you experience any discomfort with new contacts.

Symptoms that could result from an incorrect base curve include:

• Redness
• Irritation
• Dryness
• Infection
• Long-term damage

A base curve is a required part of any valid contact prescription. Even though the soft disposable contacts are made to make almost anyone comfortable, it’s still important to determine the curve that is correct for you for maximal cornea comfort and health. 

Think of it like buying a new pair of shoes. When fitting shoes, it’s not just important to know shoe size, but it is also important to know the arch and width of the foot. If you randomly choose a fit that is not your own, your foot won’t get its maximal comfort either. 

What does Deliver Contacts Do to Ensure that I Have the Correct Base Curve?

We make sure that every prescription we receive has all of the necessary details included in the script, including the Base Curve. 

Some products that we carry are limited in base curve selection, but we ensure that you have the ability to specify your base curve at the time of order. This way, you can ensure that your order with us aligns with your correct prescription.

Frequently Asked Questions (FAQs)

What does “base curve” on contacts mean?

The Base Curve of a contact lens is the measurement of the back curvature of the contact lens, the “fitting curve”. Base Curve is the term that is used to describe the caliber of steepness of the lens needed for properly matching the shape of the person’s cornea of their eye.

What is the average base curve (BC) number for contact lenses?

The normal range (in millimeters) for soft disposable contact lenses is from 8.3mm through 9.0mm, with 8.6mm being the average base curve. 

Does the base curve on contacts matter?

A base curve is a required part of a contact prescription. Even though the soft disposable contacts are made to make almost anyone comfortable, it’s still important to determine the curve that is correct for maximal cornea comfort and health. If the fit is not right, then our eyes may become red, irritated, dry, infected, or damaged.

How do I know my BC number for contacts?

You’ll find out what your specific base curve is during an eye exam with a doctor. Once the doctor understands the steepness of your cornea and combines that information with other details learned during the exam, then they can choose the base curve that is most suited to your eye. 

Can I change my contact lens base curve without consulting an optometrist?

You should not try to change your contact lens base curve without consulting your optometrist. In fact, it is a required value on your prescription to be able to order contact lenses. The base curve is a crucial parameter that determines how well the lens fits your eye. Using a lens with an incorrect base curve can lead to discomfort, poor vision, and even potential eye health issues. Always consult your eye care professional if you want any changes to your contact lens prescription.

Can I wear contact lenses with a different base curve than prescribed?

While contact lenses with a different base curve than prescribed might fit and even feel comfortable initially, they could lead to issues over time. An incorrect base curve might cause the lens to fit too tightly or loosely, which can lead to complications like redness, irritation, blurred vision, and potential eye damage. Therefore, it’s crucial to always use lenses with the base curve specified in your prescription.

Do I need to get a new base curve measurement for every new pair of contact lenses?

If you’re switching to a different brand or type of lens, it’s a good idea to have your fit reassessed by your optometrist.

How often should I check if my base curve prescription has changed?

An annual eye examination is typically sufficient to ensure your contact lens prescription, including the base curve, is still suitable for your eyes. However, if you experience discomfort or irritation, it’s a good idea to schedule an appointment with your eye care professional sooner.