Hello, I'm not an expert of the subject but what I understood is that the iris don't pop out, it's pop inward. BUT the transparent cornea pop outward. So the light is masked by the right border and highlight the left part. The white dot is the light reflection on the cornea so on the right part. The white of the eyes is also a sphere going outward so the light is at the right and the shadow at the left. Hopes it helps.
Ah sorry googled some stuff. I mentioned the iris but I confused it with the cornea it seems, my bad. Still then, I'd expect the section of the cornea that you have painted yellow to be in shadow, and the section of the iris that you have painted blue to be yellow.
The point is : the iris is opaque, the cornea is not. So the yellow cornea is in the shadow but we don't see it (transparent like glass), We see the iris enlighten underneath. You can forget the cornea since it is transparent (except for the small white dot) and focus only on the iris which is concave.
Ah! I think I got it now. The iris is opaque and shaped like a bowl that is upright, so the highlight correctly showcases a transition in the planes there. At the same time, the cornea is also shaped like a bowl, but upside-down ( it pops out ), however it is transparent, so it does not cast a shadow on the left part of the iris. Merely the opposite, since as we said the iris is like an upright bowl a little bit. Tysm!
I think you got it ! Happy to be of help