DefinitionRed eyes are caused by enlarged, dilated blood vessels, leading to the appearance of redness on the surface of the eye. Alternative NamesBloodshot eyes; Red eyes; Scleral injection; Conjunctival injectionConsiderationsThere are many possible causes of a red eye or eyes. Some are cause for concern; some are medical emergencies. Others are of no consequence or concern at all. The degree of redness or appearance of blood usually does not correlate to how serious the situation is. It is generally more important whether you also have eye pain or impaired vision.Common CausesBloodshot eyes appear red because the vessels in the surface of the white portion of the eye (sclera) become enlarged and irritated. This may result from extremely dry air, sun exposure, dust, foreign body, an alle