apple of one's eye" 這一詞最早出現於聖經裡：詩篇17:8：Keep me as the apple of the eye, hide me under the shadow of thy wings;《申命記》三十三章的第十節：In a desert land he found him, in a barren and howling waste. He shielded him and cared for him; he guarded him as the apple of his eye。跟東方一樣，在西方，人們也一直都把蘋果視為一種吉祥的水果。不是還有另一句英文諺語："An apple a day, keeps doctor away"。所以"apple of one's eye"就是指「珍貴的東西」，也就常被引申為「珍愛的人或物」。
