[2] 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.
[3] The earliest appearance of the term is found in the ninth-century Old English translation of the Latin Cura pastoralis attributed to Alfred the Great.
[2][4] The sense "pupil" appears to be the meaning Shakespeare used in his 1590s plays A Midsummer Night's Dream, and Love's Labor's Lost.
In the A Midsummer Night's Dream, the fairy character Oberon has acquired a flower that was once hit by Cupid's arrow, imbuing it with magical love-arousing properties, and drops juice of this flower into a young sleeping man's eyes, saying "Flower of this purple dye, / Hit with Cupid's archery, / Sink in apple of his eye".
However, Hebrew scholars generally regard this phrase as simply referring to the "eyeball".