The most interesting disease to know

 It is a rare condition called polycoria. It is when people have more than one pupil.

Each has its own sphincter muscle. Unfortunately, it does not confer any benefits or superpowers.

For some it has no side effects and for others it impairs their vision to the point that it is difficult to see with that eye (many who have it cannot see at all).

It is usually not as pretty as in the first photo and often looks strange. If I had to choose one and it didn't affect my vision I guess I would choose the lower right:

It can also occur with an injury to the pupil, giving a similar appearance, but in this case it is usually possible to repair it with sutures, which is how polycoria is also fixed.

If I could sell any one of my seven senses for millions of dollars, I think vision would be one of the last to go.