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Eyebright is one of the more common plants used to make witcher potions. In particular, it is used for the Cat potion.

The witcher smiled wryly — he knew what he looked like. After drinking a mixture of banewart, monk's hood and eyebright the face takes on the colour of chalk, and the pupils fill the entire iris. But the mixture enables one to see in the deepest darkness and this is what Geralt wanted.
— pg(s). 22, "The Witcher", in the collection The Last Wish (US edition)