Eye health resources

How to read contact lens prescriptions

Q: Can you convert your glasses prescription to a contact lens prescription?

Since eye glasses sit away from your eyes and not on them like contact lenses, the prescription can be a little bit different. Additionally, glasses prescription will not provide the BC that is needed for the lens to fit on your eye correctly. You may be able to find conversion calculators online, but contact lenses are medical devices, so you’ll need an eye doctor to write you a prescription specific to contact lenses.

Q: What does +0.25 mean?

A sphere prescription of +0.25 means that you have very minor farsightedness. A cylinder prescription of +0.25 means that you have a very minor astigmatism.

Q: What is power PWR/SPH?

PWR (Power) or SPH (Sphere) is a measurement that tells you how strong your contact lenses or glasses need to be to help you see clearly. A “plus” number (+) means it helps with farsightedness, and a “minus” number (-) helps with nearsightedness.

Q: How much weaker should contacts be than glasses?

It isn’t that contact lenses should be weaker than glasses, but that contact lenses sit on your eye rather than in eyeglass frames, meaning the prescription will be different. This is why you can’t directly convert an eyeglass prescription into a contact lens prescription.

Q: Is 0.25 astigmatism a lot?

Since prescriptions are measuring in increments of 0.25, this is the lowest level of astigmatism a person can have. In fact, most people have this level of astigmatism or more.

Q: What does BC mean for contacts?

When referring to contact lens prescriptions, BC stands for Base Curve, or the curvature of your contact lens. Depending on the shape of your eye, certain base curves may fit better than others.

Q: How bad is my astigmatism?

It’s important to talk to your eye doctor to understand the severity of your astigmatism. Generally speaking, cylinder prescriptions -2.50 and above are considered high or severe myopia. This level of astigmatism can cause significantly blurred or distorted vision.