Subconjunctival hemorrhage occurs when a small blood vessel under the conjunctiva breaks and bleeds. It may occur spontaneously or from coughing, heavy lifting, or vomiting. In some cases, it may develop following eye surgery or trauma. Subconjunctival hemorrhage tends to be more common among those with diabetes and hypertension.

While it may look frightening, a subconjunctival hemorrhage is essentially harmless. The blood becomes trapped underneath the clear conjunctival tissue, much like a bruise. The blood is visible because it shows through the thin, clear conjunctiva. The blood naturally absorbs within one to three weeks and no treatment is required.