Figuratively it is something, or more usually someone, cherished above others. What's the origin of the phrase 'The apple of my eye'? 'The apple of my eye' is an exceedingly old expression which first appears, in Old English, in a work attributed to King Aelfred (the Great) of Wessex, AD 885, titled Gregory's Pastoral Care.

The phrase " apple of my eye " refers in English today to something or someone that one cherishes above all others. Originally, the phrase was simply an idiom referring to the pupil of the eye. Originally this term simply referred to the "aperture at the centre of the human eye", i.e. the pupil, or occasionally to the whole eyeball.