How come some peoples eyes glow and some do not?

Mine used to, they were lumicent like christmas trees. Literally, and I see some famous people have the same thing and then other peoples eyes are perfectly normal. But even on my drivers license you can see it.

I've noticed attractive people have a gleam in their eyes. Whether the eyes are blue or brown, there is a certain gleam.. its strange.

I don`t know why, maybe there is a health aspect to it.

I find more puzzling why some peoples eyes change colors?. For example mine go from light brown to green to even yellow?.

I have found no rational explanation for it, not that I have really reserched though....

I guess I`m lazy and I want someone to tell me.

That is nutty , but I have noticed that. But it must be like what happens to platinum blond babies. They grow up and their hair gets darker. They also don't look as pasty white as they did in their childhoods.