The sudden appearance of blood in your eye is probably a subconjunctival haemorrhage. Although it might look worrying, it's usually a harmless condition which isn't painful or serious.

The haemorrhage occurs when one of the tiny blood vessels in your eye leaks under the conjunctiva.

It's not known why some vessels leak; it might occur spontaneously or may follow a violent sneeze, cough or vomiting.

The blood is usually reabsorbed by the body and disappears within a few weeks. However if you do experience pain or there are any changes in your vision you should see your optician immediately.