In manga and anime, when a character's eyes shine light—as in: they glow—turning into four-pointed sparkles, it's typically because they've set their eyes on something, like a predator ready to pounce the prey, or because they've just seen or heard something that piqued their interest extremely.
It's usually accompanied by a grin. In some cases, it's just an exaggerated way to draw sparkling eyes.
Right: Shikada Kokonotsu 鹿田ココノツ
Anime: Dagashikashi だがしかし (Episode 1)