I wanted to make certain before I replied to this but according to Brian Muir they did NOT use ski goggles. The lenses were custom made. Mr Muir himself sculpted the lens shape into the clay master (this is from a post by Mr Muir on the Prop Den from 2008).
My memory was foggy on this point so I wanted to be sure. My recollection was that we spent ages searching for goggles with the exact lens shape/color and while we got close we never found anything exact. Then Brian Muir came along and set us straight so we dropped it. I don't know how much money I spent on ski goggles that didn't work, lol.
Also, I wanted to suggest a clarification regarding the asymmetry of the helmet. On page 24 of his book "In the Shadow of Vader" Brian Muir writes: "I have been asked many times in recent years if the asymmetrical look of the face was intentional or just a result of the moulding process. I had put a slight difference in the cheek areas so that it would not have the appearance of a robot but during the moulding and casting process, it became slightly exaggerated." So the asymmetry was intentional just not as much as we got, lol.
Dave C