About Your Contact Lens Prescription
A contact lens prescription might look like a bunch of confusing numbers that have no meaning, but each part of your prescription has an impact on your vision. If you're new to contacts or you've been getting them for years, you may be wondering how to read the prescription. Read on to learn more about contact lenses and how the numbers your eye doctor uses play a role in your eyesight and help you achieve better vision.
What is BC for Contacts?
Your contacts should have something to indicate the BC, or Base Curve. This number determines what kind of fit you need in order for your contact lenses to meet with the curve of your eye. Your eye doctor will usually write the BC number in millimeters, and they may include other descriptors. Some words you may see near the BC number include flat, medium, or steep. These words describe the curvature of your eye and help determine how to shape your lenses for the best fit.
Other Parts of a Contact Lens Prescription
Apart from your BC or Base Curve, there are other elements of a contact lens prescription. These may include:
- Power Sphere: This number will show whether you're near or farsighted and it determines how much correction your eyes need. For those who are farsighted, the number will begin with a plus sign, and for those who are nearsighted, it will start with a minus sign. The number is then increased from 0 in 0.25 diopter increments and the higher this number, the more vision correction you need.
- Diameter: The DIA or Diameter determines the width that will best fit your eye, and it's also written in millimeters.
- Cylinder: You'll only see this number if you are getting toric lenses for astigmatism. The cylinder is always a negative number and determines the amount of astigmatism and any extra visual-related requirements to correct it.
- Axis: Since astigmatism is caused by an irregular curve of the eye, the axis dictates the angle of correction needed to help you see clearly. You'll see the Axis displayed anywhere from 0 to 180 degrees.
- Addition or ADD: This number is for those dealing with presbyopia and determines how much vision correction is needed so you can see clearly at close distances. The ADD number is always positive and is between 0.50 and 3.00. It may also be referred to as high, medium, or low for some contact lens brands.
- Dominant: People who need multifocal or bifocal contacts will need identification for the dominant and non-dominant eye. The dominant eye is usually noted with the letter D, which prioritizes distance vision. The nondominant eye noted with the letter N prioritizes near vision.
Contact Lenses and Your Prescription
You must obtain a prescription from your eye doctor in order to purchase contacts in the United States. Contacts are a medical device and if they don't fit properly, it can potentially cause a problem like vision loss, discomfort, infection, swelling, and more. Your contact prescription should only be valid for one year from the issuance date. You will need to schedule a new eye exam every year to confirm your current prescription is still correct or to get a new one.