Apple of my eye
The phrase apple of my eye refers to something or someone that one cherishes above all others. Apple of eyes is a very famous idiom and very commonly used in English language, the meaning of apple of eye is: the person of whom one is extremely fond, favorite, loving, for example "She has three children, but her youngest son is the apple of her eye." 
hwæt on ðæs siwenigean eagum beoð ða æpplas hale, ac ða bræwas greatigað, forðam hie beoð oft drygde for ðæm tearum ðe ðær gelome of flowað, oððæt sio scearpnes bið gewird ðæs æpples.
The pupils of the bleared eyes are sound, but the eyelashes become bushy, being often dried because of the frequent flow of tears, until the sharpness of the pupil is dulled.
Shakespeare also used it in the 1590s when he wrote A Midsummer Night's Dream:
"Flower of this purple dye, / Hit with Cupid's archery, / Sink in apple of his eye".
It also appears in the King James Bible Translation from 1611:
He found him in a desert land, and in the waste howling wilderness; he led him about, he instructed him, he kept him as the apple of his eye.
in the Book of Psalms 17:8
Keep me as the apple of the eye, hide me under the shadow of thy wings
in Proverbs 7:2
Keep my commandments, and live; and my law as the apple of thine eye.
Lamentations 2: 18
Their heart cried unto the Lord, O wall of the daughter of Zion, let tears run down like a river day and night: give thyself no rest; let not the apple of thine eye cease.
as well as in Zechariah 2:8
For thus saith the LORD of hosts; After the glory hath he sent me unto the nations which spoiled you: for he that toucheth you toucheth the apple of his eye.
The original Hebrew for this idiom, in all but Zechariah 2:8, was 'iyshown 'ayin (אישון עין), and can be literally translated as "Little Man of the Eye." This is a reference to the tiny reflection of yourself that you can see in other people's pupils. Other KJV translations of the word 'iyshown include dark and obscure, as a reference to the darkness of the pupil.
This Hebrew idiom is surprisingly close to the Latin version, pupilla, which means a little doll, and is a diminutive form of pupus, boy, or pupa, girl (the source also for our other sense of pupil to mean a schoolchild.) It was applied to the dark central portion of the eye within the iris because of the tiny image of oneself, like a puppet or marionette, that one can see when looking into another person's eye.
In Zechariah 2:8, the Hebrew phrase used is bava 'ayin (בבה עינ). The meaning of bava is disputed. It may mean "apple"; and if so, the phrase used in Zechariah 2:8 literally refers to the "apple of the eye." However, it appears that most Hebrew scholars think this Hebrew phrase communicated the meaning conveyed by the English word, "eyeball" (E.g., see The Hebrew and Aramaic Lexicon of the Old Testament, vol. 1, p. 107).
"Poor Richard was to me as an eldest son, the apple of my eye."
- "The meanings and origins of sayings and phrases". Phrases.org.uk. Retrieved October 17, 2012.
- Gregory I. Pope (January 1, 1999). King Alfred's West-Saxon Version of Gregory's Pastoral Care. Elibron.com. p. 68. ISBN 978-1-4021-9636-2. Retrieved October 17, 2012.
- Transactions and Proceedings of the American Philological Association, Vol. 73, 1942[dead link]