The creature can’t see, which means its targets have total concealment against it. The creature takes a -10 penalty to Perception checks. The creature grants combat advantage. The creature can’t flank.A blinded creature cannot have combat advantage against anyone. This condition applies to creatures that have been temporarily blinded, such as by exposure to brilliant light or a magical darkness clouding their eyes. It doesn’t apply to creatures that are naturally blind (such as oozes).
Published in Player's Handbook, page(s) 277, Player's Handbook 3, page(s) 220, Rules Compendium, page(s) 229, Monster Vault: Threats to the Nentir Vale, page(s) 122.