When a character is afflicted with Blindness it can mean true Blindness from the loss of an eye, manipulation, deep darkness, poison, or simply being blindfolded properly. However it happens, characters will have DISADV on (or be unable to perform at the GM's discretion) many actions which require sight. A common example is attacking. All attacks made by the blinded character have DISADV and all enemy attacks made against them have ADV.
Blindness: Earth 5