Princess Luna Eye Animation

Y'know, I've long wondered why so many characters have eyes that start glowing when they power up.

I mean, why the eyes? Emitting light from an organ that's supposed to take in light would seem like it should blind you. And even if the light is just a by product of the power build up, why would it only escape out of the eyes (and optional electric crackle/power aura - but that's another rant)? Why not the mouth, or the ears, or nose, or other body cavities?

I know I'm over thinking it; and yet...