The conjunctiva is the thin, moist, transparent membrane that covers the white part of the eye (called the sclera) and the inside of the eyelids. The conjunctiva is the outermost protective coating of the eyeball.
The conjunctiva contains nerves and many small blood vessels. These blood vessels are usually barely visible but become larger and more visible if the eye is inflamed. These blood vessels are somewhat fragile and their walls may break easily, resulting in a subconjunctival hemorrhage (bleeding under the conjunctiva). A subconjunctival hemorrhage appears as a bright red or dark red patch on the sclera. This does not require treatment and will resolve spontaneously in 3-6 weeks.
The following can occasionally result in a spontaneous subconjunctival hemorrhage: