Asthenopia

Weak, tiredand painful vision; the result of straining somepart of the mechanism of the eye. Vision maybe normal. It is subdivided into three kinds:retinal, muscular, and accommodative.

Source: Ophthalmic Dictionary including pronunciation, derivation and definition of the words used in Optometry and Ophthalmology by James J. Lewis, Oph. D. Professor of Optometry in the Northern Illinois College of Ophthalmology and Otology, Chicago.