WordNet (r) 3.0 (2006):

eyestrain
    n 1: a tiredness of the eyes caused by prolonged close work by a
         person with an uncorrected vision problem [syn:
         eyestrain, asthenopia]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "eyestrain":
   brain fag, debilitation, debility, enervation, enfeeblement,
   faintness, fatigue, goneness, heart strain, jadedness, languor,
   lassitude, mental fatigue, mental strain, overstrain,
   overtiredness, sleepiness, stance fatigue, strain, tiredness,
   weakness, wearifulness, weariness