A black eye is a relatively common result of some injury to the face or head. A black eye is caused when blood and other fluids collect in the space around the eye.
Most black eyes are relatively minor injuries.
Many will heal on their own in a few days. Sometimes they signify a more serious injury. The tissues around the eye may be significantly discolored and swollen without any injury to the eye itself. Think of it as a bruise around the eye. Like a bruise , as a black eye heals, the swelling around the eye will decrease, and the bruise will gradually fade away.