A _long-sighted_, or _hypermetropic_, eye is one which can focus light from distant objects, but not from near objects. In such an eye the ball is too short for the converging power of the lenses and the image tends to form back of the retina (_B_, Fig. 164). These defects in focusing are remedied by wearing glasses with lenses so shaped as to counteract them. Short-sightedness is corrected by concave lenses and long-sightedness by convex lenses, as shown in diagrams above. _Astigmatism_ is another defect in the focusing power of the eye. In astigmatism the parts of the eye fail to form the image in the same plane, so that all portions of the object do not appear equally distinct. Certain parts of it are indistinct, or blurred. The cause is found in some difference in curvature of the surfaces of the cornea or crystalline lens. It is corrected by lenses so ground as to correct the particular defects present in a given eye. Whenever defects in focusing are present, particularly in astigmatism, extra work is thrown on the ciliary muscle as well as the muscles that move the eyeballs. The result is frequently to induce a condition, known as _muscle weakness_, which renders it difficult to use the eyes. Even after the defect in focusing has been remedied, the muscles recover slowly and must be used with care. For this reason glasses should be fitted by a competent oculist(126) as soon as a defect is known to exist. When one is unduly nervous, or suffers from headache, the eyes should be examined for defects in focusing (page 326). *Eye Strain and Disease.*—The extra work thrown upon the nervous system through seeing with defective eyes, especially in reading and other close work, is now recognized as an important cause of disease. Through the tax made upon the nervous system by the eyes, there may be left an insufficient amount of nervous energy for the proper running of the vital processes. As a result there is a decline of the health. Ample proof that eye strain interferes with the vital processes and causes ill health, is found in the improvements that result when, by means of glasses, this is relieved. *The Eyes of School Children.*—School children often suffer from defects of vision which render close work burdensome, and cause headache, general nervousness, and disease. Furthermore, the visual defects may be unknown both to themselves and to their parents. Pupils showing indications of eye-strain should be examined by an oculist, and fitted with glasses should defects be discovered.(127) The precaution, adopted by many schools, of having the eyes of all children examined by a competent physician employed for the purpose, is most excellent and worthy of imitation.