The phrase "apple of the eye" refers to someone or something that is highly valued and cherished. There are several synonyms for this phrase, including "jewel in the crown," "prized possession," "treasure," and "darling." These phrases all express the same sentiment as the original phrase, highlighting the deep emotional attachment and importance that we place on certain people or things. Other similar phrases include "heart's desire," "pet project," and "beloved." All of these phrases emphasize the strong personal connection that we feel towards someone or something that we hold dear, making them all effective ways of expressing our feelings of affection and admiration.