Thank you for writing JustAnswer with your health question.
This is called a subconjuntival hemmorage. It can be caused by straining, or for no clear reason. It may occur more often in those with high blood pressue. Examples of straining that can cause this are, sneezing, coughing, vomiting, or lifting a heavy object.It will reabsorb like a bruise. There is no treatment. A warm compress, could theoretically cause the bleeding to expand (heat increases circulation, cold decreases circulation) But if your eye is "itchy" it may indicate allergies or irritation and perhaps you have scratched it, without realizing it. Do not use visine or any other eye drop that causes the vessels to constrict. These types of eye drops could delay healing. A simple saline eye drop or tear replacement eye drop would be fine and might be soothing.Have you had your blood pressure checked? This would be my suggestion, just to make sure it is within normal limts, although this is likely not the cause.If you need anything clairified don't hestitate to write me back.
Additionally, if this keeps increasing, or does not begin to absorb, you would need to see a doctor, preferably a opthamologist.