I thought the title was mundane after viewing:
Eyes Wide Open: General Society, and all of the "facades" that people have in the movie. Like that director/Actor who had the girl OD was the first insight into the Underground of all those rich folks.
Eyes Wide Shut: You think you know everyone by their facades, and that's how you relate to them. But in reality, the cover of the book, is just a cover, so what you think you know, you don't, and what you think is true isn't, even in NK, and TC's life, as we saw was full of misconceptions (looked like a great, happy, successful couple, but had problems themselves) so in reality even though you thought your eyes were wide open, they were really WIDE SHUT.
That's my 02c.