Definitions for eyestrainˈaɪˌstreɪn
Random House Webster's College Dictionary
discomfort in the eyes produced by excessive or improper use.
Origin of eyestrain:
a tiredness of the eyes caused by prolonged close work by a person with an uncorrected vision problem
tiredness or pain in the eyes, sometimes accompanied by headache, caused by excessive or improper use of the eyes, or by uncorrected defects of vision