apple of someone's eye

The story

1. Old English · inherited fromæppel on the ēagan
2. Middle English · inherited fromappel of the eie“pupil of the eye; cornea; (figurative) something highly valued”
3. English todayapple of someone's eye

PIE word *h₂ébōl From Middle English appel of the eie (“pupil of the eye; cornea; (figurative) something highly valued”), from Old English æppel on the ēagan, used in biblical texts (Deuteronomy 32:10, Psalm 17:8; Proverbs 7:2, Lamentations 2:18, and Zechariah 2:8; compare the quotations) to designate the pupil of the eye as something precious to be protected. The use of "apple" in English is apparently due to the pupil or cornea being thought of as a solid, globular object.