See what those Special Editions have done?
Sorry Sean but there were MANY instances where Dave Prowse's eyes could be seen behind those red lenses back in the pre-SE days. Heck, one can still see them on the LD edition of the movie (along with Kenny Baker's face in R2's clear eye while on the sandcrawler). All that's been,
ahem, fixed now in the special editions.
Granted, the concept was..."What is this guy? Machine or man?", but the limitations of time and technology in the '70s (and no army of fans ripping things to shreds via the internet LOL) made those eyes quite visible...