Your eyes are permeated by fine blood vessels, and it's almost unavoidable that one of them bursts. Having the white of your eye literally turn blood red looks scary, but it may not be really serious, according to eye specialists.
"If it happens spontaneously and for no apparent reason, the redness is often harmless and disappears on its own after a while," said Dr. Philipp Steven, senior physician in the Department of Ophthalmology at Cologne University Hospital.
The white part of your eye is covered by a clear membrane called the conjunctiva, under which are many tiny blood vessels – or capillaries – that can easily burst. The medical term for this is a subconjunctival hemorrhage.
"Pressure from a coughing fit or strong sneeze can even do it," explained Dr. Andrea Lietz-Partzsch, who has two ophthalmology practices in Berlin.
Heavy lifting or straining to have a bowel movement may also cause a capillary in your eye to burst. The leaking blood can spread over part or all of the eyeball. "Simply rubbing your eye can cause a hemorrhage as well," Steven said.
If you have recurrent subconjunctival hemorrhages within a short period of time, you should be examined by an opthalmologist. You should see an eye doctor promptly if a burst capillary results in impaired vision or your red eye was caused by an injury, such as being struck by a ball or scratched by a thorn while you were gardening.
But if you get a red eye and notice no ill effects, you can generally wait to see if the redness goes away. Should it persist for more than two days though, it's advisable to make an appointment with an opthalmologist to determine the cause.
It's also a good idea to be examined by an internist as well, according to Andrea Lietz-Partzsch, "because a red eye can also be a symptom of a serious illness."
Recurrent burst capillaries in the eye may be an indication of high blood pressure, which, if left untreated, can at worst lead to a stroke.
A blood-clotting disorder is another possible cause, which should be treated as well. And if you regularly take certain medications, including blood thinners, you can be more prone to localized bleeding outside of blood vessels – "not only in your eye, but in other parts of the body too," Steven says.
"It's also possible that your eyes, perhaps due to the aging process, are simply overly dry," pointed out Lietz-Partzsch. Dryness often makes the eyes so sensitive that even rubbing them lightly can cause redness. A doctor can recommend an ointment to alleviate the symptoms.
As Stevens notes, subconjunctival hemorrhages "almost always" occur in just one eye at a time. Redness in both eyes at once is often due to an allergy or infection with a virus or bacteria. Conjunctivitis (inflammation of the conjunctiva) or keratitis (inflammation of the cornea) often cause reddened eyes as well.
If you have a red eye from a burst capillary, you should avoid strenuous physical work, intensive sport and heavy lifting to allow the blood in your eye to recede. "Otherwise," Stevens warns, "there's a risk of a capillary bursting again and prolongation of the redness."