There is a Variant Rule on page 27 of the DMG called Damage to Specific Areas.
Sometimes, despite the abstract nature of combat, you’re going to want to apply damage to specific parts of the body, such as when a character’s hands are thrust into flames, when he steps on caltrops, or when he peeks through a hole in the wall and someone shoots an arrow into the hole from the other side. (...)
The rule suggestsuggests to apply a –2 penalty to any action that the character undertakes using that portion of his body. There There is a table that shows which actions would suffer this penalty. It also says that
Severe damage to both eyes causes a character to become blinded.
Severe damage to both ears causes a character to become deafened.