What do the POWER and BC measurements mean on my contact lens prescription?
Before you can get your contact lenses, you will need to go to your optometrist for a professional eye exam. This test will give your optometrist the information they need to identify your contact lens prescription, which is vital for ensuring you get the right lenses for your eyes. Without the correct prescription you can experience headaches, dizziness, eye strain and other uncomfortable symptoms while wearing your contact lenses. That's why it's important to ensure you visit a qualified optometrist first. Your prescription will contain a number of measurements and numbers that might seem like jargon to you at first. However, they each contain an important piece of information about your eye and the strength of your vision.
The 'Power' or 'Sphere' section of your prescription indicates how much correction your vision needs to function properly. This is sometimes written as PWR/SPH or just PWR. This will be given in the form of a number, which will have a minus or plus sign preceding it. The further this number is from zero, the more correction your eyes need. A minus sign before it indicates myopia or shortsightedness, while a plus sign means you have hyperopia or longsightedness.Don't worry if your left and right power measurements are different. Many people require different levels of correction for each eye, and in some cases the gap between the two can be quite significant. The 'BC' or base curve measurement indicates the back curvature of your contact lens, in millimetres. This is important for comfort, as the BC of your contact lenses should match your eye's natural curve as closely as possible to ensure a better fit when you are wearing your contact lenses. It also means your contact lenses will be less likely to fall out. A lower BC number means a steeper curve of your cornea (the clear front surface of your eye). A higher BC number means your cornea is flatter.