A black eye, periorbital hematoma, or shiner, is bruising around the eye commonly due to an injury to the face rather than to the eye. The name is given due to the color of bruising. The so-called black eye is caused by bleeding beneath the skin and around the eye. Sometimes, a black eye indicates a more extensive injury, even a skull fracture, particularly if the area around both eyes is bruised, or if there has been a prior head injury.
Although most black eye injuries are not serious, bleeding within the eye, called a hyphema, is serious and can reduce vision and damage the cornea. In some cases, abnormally high pressure inside the eyeball (ocular hypertension) can also result.
Progression of periorbital hematoma over ten days: the blood is gradually absorbed, but the iron-laden pigments in the blood remain in the tissue leaving a discoloration that persists for longer.
Despite the name, the eye itself is not affected. Blunt force or trauma to the eye socket results in burst capillaries and subsequent haemorrhaging (hematoma). The fatty tissue along with the lack of muscle around the eye socket allows a potential space for blood accumulation. As this blood is reabsorbed, various pigments are released similar to a bruise lending itself to the extreme outward appearance.
The dramatic appearance (discoloration purple black and blue and swelling) does not necessarily indicate a serious injury, and most black eyes resolve within a week.