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Red eyes are caused by enlarged, dilated blood vessels, leading to the
appearance of redness on the surface of the eye.
Considerations. 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.
Causes. 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
subconjunctival hemorrhage. Although this bloody area may appear alarming,
it is a fairly common occurrence and of little significance. If you notice a
bloody blotch in one eye that doesn't hurt, but just looks bad, don't worry.
It generally clears up on its own within a week or two.
Eye infections or inflammation can occur in different locations. They cause
redness as well as possible itching, discharge, pain, or vision problems:
- Blepharitis. Inflammation of the eyelash follicles along the eyelid. It is
caused by skin bacteria. Itching is common, and your eyelids may appear
greasy or crusty.
- Conjunctivitis. Inflammation or infection of the membrane that lines the
eyelids and coats the surface of the eye (the conjunctiva). This condition
is often referred to as "pink eye." It may be caused by a virus, bacteria,
allergy, or irritation. If caused by an organism, this is highly contagious.
- Corneal ulcers. Often caused by a bacterial or viral infection. (The
cornea is the outer covering of the eye.)
- Uveitis. Inflammation of the uvea, which includes the iris, ciliary body,
and choroid. This is often related to an autoimmune disorder, infection, or
exposure to toxins. Often, only the iris is inflamed, which is called
iritis.
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