A black eye is simply a bruise around the eye. The most common cause of a black eye
is a blow to the eye or the nose. Depending on where the blow lands, one or both eyes
may be affected. When an object strikes the eye, the force of impact breaks delicate blood vessels in the eyelids and surrounding tissues. Since the skin around the eye is
very loose, fluid tends to accumulate easily beneath it. 

Blood collected under the skin causes the black or blue discoloration. Because the skin around the eye is relatively thin and transparent compared to skin in other parts of the body, the black and blue color of a bruised eye may seem darker and more intense than bruises elsewhere on the body. Gravity encourages the blood to pool in the eyelid
and area under the eye.

Most swelling and discoloration disappear within seven to
10 days after the injury. Just as with bruises elsewhere on the body, the color of the
skin around the eye normally changes from black or blue to greenish-yellow tones as the blood trapped beneath the skin breaks down and is reabsorbed. Allergic reactions, and insect bites can also cause pronounced swelling around the eyes but these conditions
do not result in the black and blue appearance found in impact injuries.

Home Treatment

• Ice packs or cold compresses during the first twenty-four hours, particularly when used promptly after being injured, could help minimize bleeding and swelling.  Ice wrapped in a washcloth or a baggie of frozen veggies make an effective ice pack.
   
• Keep your head elevated (sleep with an extra pillow, for example) to help limit swelling and pooling. Over-the-counter pain relievers, such as acetaminophen, can help relieve inflammation and minimize discomfort. Avoid aspirin since it decreases the blood's ability to clot.
   
• On the second day following the injury, applying warm washcloths or compresses can help increase circulation to the injured tissue. This aids in the re-absorption
  of any leftover blood that has collected at the injury site, promoting healing.

Most black eyes are not dangerous. However, a black eye can sometimes be
a sign of a more serious problem, such as a fracture of the eye socket or an injury to the inside of the eye. Bleeding within the eye, called a hyphema, can reduce vision and damage the cornea. Glaucoma can also result.

• Difficulty turning the eye in any direction (looking up, down, right or left)

• Flashing lights or an increase in "floaters"

• "Bulging" of the injured eye out of its socket or a "sunken in" appearance

• Numbness in your cheek or upper teeth on the same side as the injured eye

• A cut on your eyelid or on the inside surface of your eye 

• Blood on the surface of the eye itself

• Persistent headache

• Swelling after a bee sting near the eye or from a suspected eye infection

Go to a hospital's emergency room immediately if you have any of the following:

• Broken bones or teeth

• Loss of consciousness

• Vomiting after the injury

• Change in behavior after the injury

• Inability to walk after the injury

• Blood or clear fluid from the nose or the ears

• People who take blood thinners, such as warfarin (Coumadin), or those with
  a history of bleeding problems, such as hemophilia, should go to a hospital's emergency department.

Almost all eye injuries can be prevented. To decrease your risk of eye injuries:

• Use appropriate protective eyewear at work. Studies have shown that face shields, goggles and other protective eyewear can reduce the risk of work-related eye injuries by more than 90%.
   
• If you are an athlete, always wear protective eyewear that is appropriate for your sport. Baseball and basketball cause the greatest number of eye injuries. When a baseball or basketball strikes the eye, there is a risk of more serious trauma, including fractures of the eye socket.