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Synopsis The term "weak sight" covers a vast amount of ignorance on the part of many doctors, and a multitude of distressing symptoms in many patients.  So much is now known of asthenopia and the parts involved, that it is inexcusable in any one to treat a patient by glibly informing him his sight is weak, and that all that is requisite is medicine.  In some cases medicine alone is all that is required; but in by far the large majority abnormal refraction, plus the constitutional tendency, are the disturbing factors, and in these medicines and the correcting lenses are required.  The term "asthenopia" should be confined to (1) Muscular asthenopia; a condition in which there is not sufficient power in the lateral recti muscles to keep up the necessary convergence of the visual axes for near vision.  This form is usually found in high degrees of myopia, where it is necessary to bring objects very near to the eyes; hence, where more convergence is required.  (2) Accommodative asthenopia.  This is a marked condition in many cases of hypermetropia, and is due to disturbances in the ciliary muscle, the muscle of accommodation.  Both forms of asthenopia are sources of much pain and discomfort when using the eyes, particularly for small objects.  The first mentioned has a tendency to increase the already high degree of myopia and eventually vision may become so reduced that it is incumbent upon us to give such cases the closest attention.  Eigher form amy appear at times without any manifest myopia or hypermetropia.  In muscular asthenopia the difficulty is due to convergence being in excess of accommodation.  If the difficulty be not correct by the appropriate lenses, divergent strabismus will result.  In accommodative asthenopia, accommodation is in excess of convergence, and here we may have convergent atrabismus.  In order to cure strabismus, in many instances it is only necessary to correct the visual defect by glasses.