The inability to use apparently healthy eyes for near work, without increasing discomfort or pain, is usually caused by refractive errors, or insufficiency of accommodation. In a series of 500 patients with asthenopic complaints taken consecutively from my records, the symptoms were caused by hypermetropia, astigmatism or presbyopia in 75 to 80 per cent. In 20 to 25 per cent. the asthenopia could not be accounted for in this manner, for either the optic conditions were perfect or, if not, their correction gave no relief. Some of the factors which lead to asthenopia, in the instances not dependent upon optic faults, are suggested by a study of the refractive cases, if we consider them as patients and not merely as the possessors of optically imperfect eyes. The importance of refractive errors varies according to whether we study them either in the patients of our office practice or in the population