Roubando @ Möoz answer
É uma referência da quarta parede para o público.
Dado que só vemos o efeito de 'olhos brilhantes' quando os personagens do universo não o reconheceram, isso nos diz que isso deve ser uma característica que não é aparente para eles.
Além disso, de acordo com Paul Sammon:
Ridley Scott maintains that this effect "was strictly a stylistic device, one more bit of detailing, if you like. If the replicant's eyes really did glow like that within the context of the story, then why would you need a VoightKampff machine to sniff them out?"
-Sammon, Paul M. (2000). "VIII: The Crew". Future Noir: THE MAKING OF Blade Runner.
E a importância dos olhos dentro do filme Blade Runner é enfatizada por Mary Jenkins quando ela diz:
[Ridley] Scott said of the replicants' sometimes glowing eyes: "that kickback you saw from the replicants' retinas was a bit of a design flaw. I was also trying to say that the eye is really the most important organ in the human body. It's like a two-way mirror; the eye doesn't only see a lot, the eye gives away a lot. A glowing human retina seemed one way of stating that".
-Jenkins, Mary. (1997) The Dystopian World of Blade Runner: An Ecofeminist Perspective, Cite note 6