I have no idea what you mean by a system that involves no information exchange, much less why that seems to be your starting point for arguing about the evolution of eyes.
But I can tell you step one in the evolution of eyes. Change a g-protein coupled receptor so it becomes sensitive to the presence or absence of light. That means the g-protein binds a chromophore (such as retinal), and a mutation to lysine at position 296 (in the typical opsin) in the g-protein makes it able to affect the conformational change in the g-protein that ultimately results in changed genetic expression (and thus cellular behavior).
A membrane bound chemical receptor of a certain class (GPCRs), already tied to regulated cellular behavior, becomes an opsin. The cell now reacts to the presence of light. You now have your first eye.
Done.