Confused about what the numbers and terms on your contact lens prescription mean? We’re here to help! After an eye exam, you’ll receive a contact lens prescription with specific information about your eyesight and vision correction needs. Here is a quick guide to understanding how to read a contact lens prescription and what the values on your contact lens box mean.
How To Read A Contact Lens Prescription
The three main measurements on your contact lens prescription are power, base curve, and diameter.
Base Curve
What Does BC Mean on Contact Lenses?
The base curve of the lens is marked as BC on most contact lens prescriptions. The base curve measures the steepness or flatness of the contact lens. A doctor will evaluate a lens on the eye to make sure the fit is not too tight or too loose.
The Diameter
The diameter of the lens is marked as DIA. The diameter of a lens is the same as the diameter of a circle. It measures the distance from one side of the lens to the other.
Power
The power of your prescription is marked as PWR and is made of up of 1 or 3 numbers. If there is only 1 number you have a spherical lens. It will either be a plus or a minus number. In the example below, the patient is a -0.75.
How to read a contact lens prescription for astigmatism
If your prescription has 3 numbers you have an astigmatism lens also referred to as a toric lens. One number that remains the same will be the sphere power (like a spherical lens). The second number is the amount of astigmatism, sometimes listed as cylinder or CYL.
The third number is the meridian or where the astigmatism lies. This is called the axis. In this example, the patient has a -2.25 astigmatism power aligned at 160 degrees.
OD eye vs OS eye
It is also perfectly normal to have a different prescription in each eye, but how do you figure out what lens goes in which eye? This is where you might find OD/OS on your prescription.
- Oculus dexter (OD) means “right eye” in Latin. All values for OD on your prescription will be for your right eye.
- Oculus sinister (OS) means “left eye” in Latin. All values for OS will be for your left eye.
These initials will help you to quickly understand which contacts go in either eye!
Contact lens prescription vs glasses prescription
Can I use my glasses prescription for contacts?
The simple answer to this is “no”. Glasses and contact prescriptions are not the same. Your contact lens prescription may not be the same as your glasses prescription and, in fact, for most people, it isn’t. Contact lenses sit on the surface of your eyes and glasses are perched on the face are further away, so the power of the lens will vary. To get a valid and accurate contact lens prescription, an eye exam and contact lens fitting from an eye doctor is required. Learn more about contact lenses and how to properly wear them on our contact lens care page.
How long is a contact prescription good for?
In Indiana, a contact lens prescription expires in one year. We recommend a yearly eye exam for all contact lens patients to ensure you’re seeing your best!
We hope this clears up any mystery surrounding your contact lens prescription! If you have any questions about contact lenses you can get in touch with us or schedule an appointment online at drtavel.com