In eye-operations such as Lasik and Femto, the thickness of cornea is key decision factor whether the operation is feasible. A normal thickness is between 500-600 $\mu m$. Cornea consists of a very special tissue having no blood supply and no vessels so it gets nutrients through diffusion of tear fluid and oxygen directly from air (hence in a way, it has its own respiration system not dependent on lungs).
Now I started to think the following questions:
I. What determines the thickness of cornea?
II. Is the thickness of cornea determined genetically so twins have the same cornea thickness?
III. Is the thickness determined by the environment and psychological things? Eg. how does diving affect cornea? Look it cannot get oxygen anymore through the air with the mask. What about drying? Does cornea gets too much nutrients all of a sudden from eye fluids?
IV. Does Homo Sapiens have more this kind of independent tissues? What about other animials? What determines the thickness of Cornea there?