A black eye may result from any injury to the face, but usually follows a blow to the eye or nose. Occasionally, black eyes lead to blurred vision, and sometimes, the swelling can make it difficult to open the affected eye. Both of these changes are temporary and will usually go away as the swelling goes down. If not, see a doctor for a more thorough evaluation.
The first thing to do for a black eye is to apply ice - the rule of thumb is to use ice for 20 minutes out of every hour you're awake for the first 24 hours after the injury. You can use ice cubes wrapped in a cloth, a bag of frozen vegetables wrapped in a cloth, or a commercial ice pack. Don't ever use ice directly on the skin, and do not fall asleep with ice on your face. In spite of what Hollywood portrays, it will not help to put a steak or a piece of raw meat over your eye.
You may be able to speed the healing process by taking bromelain, a pineapple enzyme available in capsule form in health food stores. Take 200-400 mg three times a day on an empty stomach (at least two hours after eating). If you notice any itching after you take bromelain, discontinue treatment. The itching may signal an allergic reaction.
Homeopathic arnica can help, as well. Use 30x potency tablets of Arnica Montana. Take four tablets immediately, letting them dissolve under the tongue, then four more every hour while awake the first day. The second day, cut back to four tablets every two hours; then four tablets four times a day and continue treatment for four to five days. Be sure not to handle the tablets themselves. Instead, shake them into the bottle cap and then toss them under your tongue.
See a doctor if you develop any of the following signs of more serious injury: persistent double vision, loss of sight, loss of consciousness, inability to move your eye, blood or clear fluid running from the nose or ears, blood on the surface of the eye itself, or persistent headache.
To prevent black eyes in the future, be sure to wear protective eye gear whenever you engage in contact sports or while you're doing carpentry or other work that could lead to an eye injury.
Andrew Weil, M.D.