VR for macbook?

I am looking for a VR headset to work with my macbook.

I heard they don't exist? But it would be quite simple to stream to a head mounted display from a Mac so I don't get why it wouldn't exist?

Is it just the speed of the Mac that is too slow? But then, can't I just turn down the resolution?

I'm not sure how a VR image is rendered. Is it kind of like the same complexity as real-time raytracing?