It was explicit in Blade Runner that the eyes are made separately -- the old technician/scientist that Roy and the other Replicant accost makes eyes.
Okay: So they are made separately and put in later? But the Replicant we see "born" in front of Nicander Wallace I think already had eyes -- that I guess doesn't mean they are not added to the body before birth.
Do we know anything about the process? Are Replicants grown or is it pretty clear they are assembled, perhaps in addition to eyes, other parts are made separately and added? If so, the sack in which the Replicant was before "birth", very much like a placenta is not a place where Replicants are grown but merely where they are kept after assembly? Is there some process they undergo after assembly that requires that they be in this placenta-like container?
Is this discussed in any of the books?