How Important is PD?

Have you experienced ordering your glasses online? Or do you still go to the optician who used to do your glasses. What if you want to order your glasses from Zenni: the #1 online eyeglasses store, but the thing is you get No PD for you from Opticians. How important is this is PD? What is PD? in other words? PD is pupillary distance, the distance between the center of the pupils in each eye. This measurement is used when preparing prescription glasses. Now what do you do if your optician does not give you your PD. In my opinion you can always ask for it. It's your right since you already have paid him in the past. Now if it's your first time to ask for your PD from an optician, it's just right to pay him a certain amount but not too much. Sometimes optician overcharge simply because they want the patients to buy the glasses from them. What if some patients want to order it online simply because it's what they can afford?