light of one's eye

noun2

1. •
   The way in which one's eyes sparkle with joy and life.

   • We look'd for the youth of the sunny glance, Whose step was the fleetest in the chase or dance! The light of his eye was a joy to see, — 1828
2. •
   (figurative) Someone beloved to the speaker, such as their life partner or offspring.

   • Mohammad Reza was his father's love — the light of his eye, as the Persian saying goes. — 2009