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. See the entire definition of Subconjunctival hemorrhage
A subconjunctival hemorrhage (or subconjunctival haemorrhage) is bleeding underneath the conjunctiva. The conjunctiva contains many small, fragile blood vessels that are easily ruptured or broken. When this happens, blood is leaked into the space between the conjunctiva and sclera.