Eyestrain

eyestrain

fatigue or irritation of the eyes, resulting from excessive use, as from prolonged reading of small print, or uncorrected defects of vision

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Eyestrain 

or asthenopia, a state characterized by a feeling of heaviness in the eyes, a dull pain in the forehead and temples (sometimes expressed as a headache), difficulty in working, diffuseness and indistinctness of previously distinct contours of objects (for example, letters in a text), and a need to close the eyes and rest them.

There are two types of eyestrain: accommodative and muscular. Accommodative eyestrain (overstrain of the accommodation muscle) develops primarily in young people suffering from hyperopia when there is need to study an object at close range for a long time. To avoid eyestrain the hyperopia must be corrected with eyeglasses, and the person must take periodic breaks from work and look into the distance. Analogous phenomena of eyestrain may be observed with uncorrected astigmatism of the eye.

Muscular eyestrain develops predominantly with uncorrected myopia and is caused by a relative weakness of the interior straight muscles of the eye, which effect convergence of the visual lines of both eyes on an observed object; upon closing one eye, all unpleasant sensations disappear. To pre-vent this form of eyestrain the myopia must be corrected, sometimes with the use of prismatic glasses (spheroprismatic lenses), and the person must take periodic breaks from work.

M. L. KRASNOV