Lens

​​A Lens is an item that is dropped by Demon Eyes. It can be sold for 1 Silver Coin each and stacked up to 99. 6 of these are required to make The Suscpicious Looking Eye, which can be used to summon Eye of Cthulhu. 3 of these are required along with 5 Copper Bars, 5 Iron Bars, and 7 Souls of Light to make the Mechanical Eye, which can be used to summon The Twins.