Origin of Expressions - "Apple of One's Eye"

My wife got me a game for Christmas called The Origin of Expressions. Working with words every day, I find it very intriguing. Especially when a card was drawn that carried a phrase that Gordon Kennedy and I used in a song a couple years ago. Here's what we wrote (from "Mosaic" [Cooper/Kennedy, ©2008] on Ricky Skaggs' album with the same title):

Photo by Abhijit Thembekar. Used with permission.

CARVED MY NAME UPON A TREE
A KNIFE INTO THE BARK
TRYING TO MAKE A MARK
SO THEY REMEMBER ME

WANTING TO MATTER TO SOMEONE
MAYBE BE A REASON WHY
BE THE APPLE OF AN EYE
BEFORE MY LIFE IS DONE

Here's how origin of the phrase "apple of one's eye" came to be (as quoted from the game card):

"In old English, the pupil was called an apple because it was thought to be round and solid like the fruit. As an important part of the eye, it was seen as precious."

Keep writing,

Ben