pliny the elder at 2011-10-20 14:20:54:
Eyes are supposed to be the gateway to the soul, and it always struck me that at some point the replicants had accidentally been given that gift by their creators.
What is it that Batty wants, or why does he want to live longer? To experience more, to have the thing he cherishes the most, his extraordinary memories, linger instead of disappearing "like tears in the rain".
Don't forget Tyrell Corp's slogan: "More human than human". imho that's what Rachel, and Deckard to some extent represent: that they're real beings, with fully intact souls, and mankind's next evolutionary step.
It's a little far, imho, to think of Deckard and Rachel as some kind of replicant Adam and Eve, but the script quotes Blake (on Ridley Scott's request), and the imagery is supposed to be some kind of vision of hell.
It would be interesting to me, to see how Ridley Scott would remake this movie, 30 years later, now that he's a much better actor's director, as opposed to the brilliant visual director he's always been. I feel he'd explore that theme more strongly.