No, you don't. If you know your prescription values, just enter the right correction in the Sphere (SPH) field. But we do recommend ordering from a prescription.
In order to purchase glasses with the right correction, it's best if you have your prescription available. We recommend using a recent prescription (less than two years old). You get your prescription from an optometrist, based on a sight test.
The most common ways to receive a prescription are:
Immediately after the sight test
By sending an e-mail to your optometrist
By calling your optometrist
When you've received your prescription, you're ready to order eyeglasses!