Blood under the conjunctival and above the sclera. "Black eye" when skin around the eye turns red or black/blue (after some time) due to hemorrhaging under the skin.

Etiology

Can be a result of one of the following or more than one of the following factors-
Coughing, lifting weights, straining, pressure over the chest or abdomen (Purtscher's syndrome)

Injury to the eye or head
Hypertension, bleeding disorders, leukemias
Associated with epidemic keratoconjunctivitis (viral)
Digitalization during sleep, specially if sleeping with kids
Idiopathic (no known cause)

Treatment

Firstly look for one of the above factors, if found treatment is directed to the cause.

For the eye no treatment is required, artificial tears may be used, cold compresses if gross swelling associated. Usually clears on its own in 2-3 weeks.

Note: There may rarely be an associated bony fracture around the eye and has to be dealt with accordingly.