Why aren't both eyes exactly the same after laser eye surgery?

Question: Is your right hand exactly the same as your left? Of course not you say but many of my patients are often quite surprised to hear that their eyes aren't a perfect matching pair. And therefore eyes will not turn out exactly the same after laser eye surgery or cataract surgery.

Your pair of eyes are not the same from birth. No human is born perfectly symmetrical. Birth marks are a perfect example- you don't have one directly in the middle of your body like you are a piece of paper folded in half, do you? And as your brain grows and develops, the two eyes compete for attention like two children trying to be the favorite child. The one that wins has more nerve and brain connections than the other and becomes your dominant eye and will always be the stronger of the two. Surgery doesn't change that. You will always favor this eye if you go take a photo with a DSLR camera or if you are playing billiards and closing one eye to take a shot.

The eyes also differ in prescription, shape, rigidity and neural innervation. Often patients will tell me one eye was more sore after surgery than the other. The obvious conclusion is " well maybe the surgery was more difficult on that side" - but that's often not the case. One eye is usually more sensitive and that's why it feels it more.

So what I am saying in short is, your eyes weren't symmetrical before surgery, why would you expect them to be exactly the same after? :)