I’m not sure if it’s an actual “sparkle” or “twinkle.” It may be from light reflecting in a person’s eye.
A person with twinkling eyes is smiling and happy. When this person talks to you, you feel like they like you. This person talks in an animated way.
It’s possible that when a person smiles or speaks in an animated fashion, their eyes change shape. This can cause light to be reflected in a certain way, causing the “sparkle” or “twinkle.”