A free mod for Witcher 3, by plasticmetal.
This mod allows you to change the appearance of your character's eyes between three sets: the base eye texture, Black Eyes, and Alt Eyes. The change is made by a special effect that is activated when the player is in a particular state.
The Alt Eyes and Black Eyes effects are activated once the following are met: Toxicity Threshold, Dark Environment, Toxicity Threshold while in Dark Environment, Any Potion Active, Cat Potion Active, Witcher Senses active, In Combat Day, Combat Dark Button Trigger, Always On, Always Off.