It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Truffles (kam'ah) are from manna (a kind of it), and their water is a cure for the eye."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12954