No,you don't need to if you can enter the prescription to the required place. Usually, you will be asked to enter your prescription after you have chosen the frame that you prefer, you can enter the value of your prescription according to the number on your prescription paper. You can send an email to service centre if you have problem entering your prescription.
You don't have to emali your eye prescription when you want to order glasses online. At the online optical store, you will enter a web page where you will find a bunch of blanks. Then you are asked to fill in the blanks with your prescription information. Then they will know what your prescription is.