We use "есть" if the point of the sentence is the existence of something.
For example, if your interlocutor doesn't know that my brother is married, you can say:
"У моего брата есть красивая жена".
If the existence is not the point, then we do not use the word "есть".
For example, I can say to a woman:
"У тебя красивые глаза."
Since I focus on the beauty rather than on the existence (my interlocuter knows she has eyes), I do not use the word "есть".