That book is one of my favorites! Isn't it interesting about why we have interchangeable eyes?
When the sunglasses factory blew up in 2999 AD, it took man kinds' eyes with them. The human race went blind for centuries!
Sunglasses used to be green. The explosion in 2999 AD took human eyes with it. In 3710 AD, people had metal implanted in their eyes. The new interchangeable eyes also had metal on them. This allowed the eyes to send signals to the brain, allowing humans to see.
Sunglasses used to be green.When people first got their eyes back, they were small. This is because they were man-made. Everyone had to get their eyes worked on to get metal gagets in their eyes. The new eyes had metal pieces on them so that they would have a metal on metal reaction.