For eyes that shine just a little brighter than naturally. This could be a usual visual trait of the character or it could indicate the character is using some sort of special power. It can also be used humorously to indicate that the character is about to respond aggressively to an opportunity or provocation, often involving an unsuspecting victim.
If only a single eye is glowing, use glowing eye instead.
This tag implicates glowing (learn more).