There is an ABer who is either an Ophthalmologist or an Optician who is excellent at answering these sort of questions.....unfortunately I cannot remember his username.
Anyway, until he sees your question, here is a rough review.
It is a bleeding at the back of the eye infront of the cornea and may be idiopathic (nobody knows the cause), due to BP or a complication of diabetes. There a rare causes, but they shouldn't concern you at the moment.
The Ophthalmic surgeon will investigate the above causes, but will probably do nothing.......masterly inactivity...........just monitor the situation.