שְׁמֹ֣ר מִצְוֺתַ֣י וֶחְיֵ֑ה וְ֝תוֹרָתִ֗י כְּאִישׁ֥וֹן עֵינֶֽיךָ׃
Keep my commandments and live, And my teaching as the apple of thine eye.
Rashi on Proverbs
like the apple of your eyes The pupil of the eye, which is like darkness, like the darkness of night.