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Red eye or blood shot eye means inflammation of conjunctiva which is called conjunctivitis or it may be due to subconjuctival hemorrhage. Common reason is viral conjunctivitis in which case one eye followed by other one occurs.It is accompanied by irritation in eye and watering. Usually goes away within few to 10 days. common cause is allergy to pollens or molds.
Second common reason is subconjunctival hemorrhage which usually occur after forceful coughing or forceful vomiting in which case very tiny blood vessels in our eye get ruptured and lead to red eye. Rare reasons for subconjunctival hemorrhage are bleeding disorders which are not manifest at this age group which you have (usually appear earlier in age).
If a person has low platelet count,it can also lead to bleeding in conjunctiva.
I recommend you to go to eye specialist for complete examination of eye and also get your blood tests done (including CBC with platelet count, PT, APTT, bleeding time) to rule out all possibilities.
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