While the mere sight of a broken blood vessel on the white of the eye (sclera) is enough to raise concerns, the condition known as a “subconjunctival hemorrhage” is usually a harmless condition. Because neither pain nor changes in vision are involved, many people do not realize that they have the characteristic bright red patches on the whites of their eyes until they see them in the mirror. Causes can range from a violent cough or sneeze to vomiting or heavy lifting. In some cases, eye trauma or roughly rubbing the eyes is enough to cause rupturing of the blood vessels underneath the clear surface of the eye (conjunctiva). In most cases, the body reabsorbs the blood within two weeks.
P.S. If you experience recurrent subconjunctival hemorrhages, schedule an appointment with the eye doctor.