This is a test of commonsense. Complete the next sentence:

How to save money on contact lenses
Keep a copy of your prescription.
You will need a prescription from within the last year to order contacts, so always ask your eye doctor for a copy after an exam. If you are considering trying to order contacts without an up-to-date prescription, know that online sellers are required to contact your doctor to verify your prescription.
Ask if your eye doctor will match online prices. If they will, this offers the best of both worlds.