Surely anyone can see who is a rep and who is not… [Well... not really!]
The use of the glowing eyes is a narrational device, a cinematic technique employed by the movie’s makers to tell the audience who is a replicant and who is not. This “device” goes outside of the movie’s reality, meaning: we, the audience, see it, but the characters in the movie *do not*. Hence the importance of the V-K test, which in the story is the only way to tell a replicant apart from a human.
Posted in: 4.2. Glowing Eyes