Not for manufacturing, but you need good designs first, something people will want to buy. And most people will want to buy something with a BIG BRAND NAME on it.
I tried buying glasses online and discovered another problem: the industry hasn't standardized on measurements. It's very difficult to buy frames online. The numbers/measurements will be, for example, for lens width and nose bridge width only — go figure how large the entire frame is. I tried, and failed, accepting that I pretty much need to visit a store.
The frame size is normally written (in Europe, at least) on the inside of one of the arms of the glasses. Find an existing pair that fits you and note the measurements. That measure, together with your prescription and PD should be sufficient to order online.
I tried buying glasses online and discovered another problem: the industry hasn't standardized on measurements. It's very difficult to buy frames online. The numbers/measurements will be, for example, for lens width and nose bridge width only — go figure how large the entire frame is. I tried, and failed, accepting that I pretty much need to visit a store.