Health Information A-Z Search Health Information Eye
rednessDefinition: Eye redness is due to swollen or dilated
blood vessels, which cause the surface of the eye to look red,
or bloodshot. Bloodshot eyes; Red eyes; Scleral injection;
Conjunctival injection There 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.
Bloodshot 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 allergic reaction, infection, trauma, or
other conditions. One common cause of a red eye is straining or
coughing. This can lead to a bright red, uniformly dense bloody
area on the sclera. This is called a sub