Bloodshot eyes are a term commonly used to describe red eyes. They are caused when the small blood vessels on the surface of the eye (sclera) become enlarged and congested with blood.
This occurs as a result of insufficient oxygen supply to the cornea or the tissues covering the eyes. Usually, bloodshot eyes are not really a cause for major concern but if eye pain or impaired vision occurs, this may be an indication of a serious problem.
A variation of this condition is a bright red, uniformly dense bloody area which forms on the sclera as a result of a small amount of bleeding. This bloody blotch usually occurs upon waking up in the morning. It does not hurt but looks awful, and will clear within a few days. This bloody blotch is called a subconjunctival hemorrhage.