There are two clinical possibilities for redness of the eyeball: 1) the presence of conjunctival congestion and 2) the presence of subconjunctival hemorrhage. Conjunctival congestion is the dilatation of conjunctival blood vessels without exudation or cellular infiltration and can be caused by a variety of environmental factors, including chemical fumes, wind, ultraviolet radiation and long-term topical medications, etc. It is the most common clinical sign of conjunctivitis in patients. Another possibility is that if a patient presents with redness of the eye, consider subconjunctival hemorrhage, which is caused by rupture of the subconjunctival vessels or their increased permeability. Generally when patients present with subconjunctival hemorrhage, the exact cause can rarely be found clinically. It can be seen when patients present with violent coughing, vomiting, or even when patients have hypertension, arteriosclerosis, or blood disorders, all of which can lead to subconjunctival hemorrhage and redness of the eyeballs.