When we started Simple Contacts, we realized most people (ourselves included) had no idea how to read their own contact lens prescription. Year after year, we go to the doctor and get a new one handed to us, but most of us don’t pay much attention to what’s on it.
Ever wondered what all those numbers actually mean? We created a handy guide to break it down for you.
First, let’s clarify that a contact lens prescription is completely different than a glasses prescription, although they are often issued together. You can tell the difference between a glasses and a contact lens prescription because a contact lens prescription will always indicate a brand name and a glasses prescription will not.
Here’s a run down of the common terms you may see on your prescription:
OD/OS: Oculus dexter (OD) is Latin for the “right eye” and oculus sinister (OS) is Latin for the “left eye”. This is the strength of lens prescribed for each of your eyes.
Fun fact: OD typically comes before OS on a prescription because when your doctor is facing you, looking at your eyes, they see your right eye on their left (first) and your left eye on their right (second).
OU: Oculus uterque, which is Latin for “both eyes”. If both of your lenses are the same strength, you may see this term instead of OD and OS individually.
Power, PWR, Sphere or SPH: Usually listed first after OD, OS, or OU, this number indicates the strength of correction needed for that particular eye. A (+) before the number indicates hyperopia, or farsightedness and a (-) indicates myopia, or nearsightedness. You may also see PL, or plano, which means the eye doesn’t need any correction and the strength is 0. Power is measured in diopters (D), and manufacturers create contact lenses in 0.25 D increments (e.g. -4.00 D, -4.25 D, -4.50 D, -4.75 D). The farther away the number is from 0, the stronger the prescription.
Base Curve or BC: This number indicates how curved the inside of your lens is. It typically ranges from 8-10 and assures that the lens fits well against your eye so it feels comfortable. A lower number means a steeper curve, and a higher number means a flatter curve.
Diameter or DIA: This is the width of the contact lens from edge to edge, measured in millimeters. This helps ensure that your contact lens will properly cover your eye.
Brand: This is the name of the specific contact lens brand/type you’ve been prescribed. Different brands of contact lenses are made out of different materials and may have unique measurements, so it’s important to know which brand of lenses your doctor has prescribed for you. By law the retailer that fills the prescription can only issue the exact brand listed--no substitutions are allowed.
Color: The color of a contact lens typically has no effect on your vision, but it's still important to get a prescription for them to make sure they fit your eyes properly. There are several types of colored lenses:
Visibility tinted lenses - These lenses have a slightly tinted color (typically blue) to help you see and handle the lens when it’s in the case.
Enhancer lenses - These lenses contain a medium tint that is intended to enhance or embellish your natural eye color.
Opaque lenses - These lenses will mask your natural eye color. They’re made with a solid ring of color around the iris and a clear circle in the middle so you can see. You can get them in all sorts of fun colors like blue, green, gray, purple, brown and more!
Cylinder or CYL: If you have an astigmatism, you’ll see an additional value for cylinder, which indicates the amount that the lens needs to correct for the astigmatism.
Axis or X: This works hand in hand with the cylinder measurement and determines where in the lens the astigmatism correction should be located.
Add Power or ADD: If you require contact lenses with bifocals in them, you’ll see this additional measurement, which indicates the amount of power the contact lens needs to allow for clear vision at a close range.
If you have further questions on your prescription, one of our team members can talk you through it, or reach out directly to your eye doctor to get additional information.
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