Blood in the eye: Medically known as a subconjunctival hemorrhage. A very common cause of a painless bloody eye usually first noticed by somebody else or by the person with it when they look in the mirror. The bleeding results from a break in a small blood vessel in the sclera, the white of the eye. This releases a tiny amount (less than a drop) of blood which is trapped underneath the conjunctiva, much like the blood in a bruise is trapped in the skin. It is called a subconjunctival hemorrhage since it occurs beneath the conjunctiva, the transparent membrane covering the sclera.
A subconjunctival hemorrhage can occur with heavy lifting, coughing, sneezing, vomiting or for no apparent reason. It looks bad and may be frightening, but is not dangerous and leaves no residual change in vision. There is no discharge from the eye. The redness may turn brown or green and everything returns to normal within 3 weeks as the blood is absorbed.
Subconjunctival hemorrhage does not require treatment. Any features not characteristic of subconjunctival hemorrhage (such as pain in the eye, a change in vision, or failure to clear up within 3 weeks, or recurrent hemorrhage) are reasons to see a doctor. Medical conditions that can upon occasion cause subconjunctival hemorrhages include bleeding disorders, blood-thinner (such as heparin and Coumadin), and high blood pressure.