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The Selection of Spectacles - Eyeglasses.Without entering into details which would be unintelligible to one who is not thoroughly versed in the structure and functions of the eye, certain hints may be given which have evident and practical value. The most important point to be remembered is that the spec tacles should be so fitted that the eyes shall look through the center of the respective glasses. It is, therefore, necessary to have the frames made differently, according as the spectacles are designed for viewing distant or near objects. For it is evident upon slight consideration, and can readily be seen by observing the eyes of another individual, that when a person looks at a distant object, the axes of the two eyes are parallel; while, when he looks at an object held close to the face, the axes of the eyes are no longer parallel, but are directed so as to meet at the object which is under examination. It is evident from this that the glasses which are intended for assisting the eyes in viewing distant objects should be somewhat further apart than the glasses which are intended for viewing near objects. One of the commonest mistakes which is made by patients in buying their own spectacles is the neglect to observe that the glasses are situated as already indicated. In some cases, it is true, one can correct this error by bending the frame of the spectacles so as to bring the glasses a little nearer together or further apart, as occasion requires ; yet it is a much better plan to procure in the first place only such spectacles as are adapted to the breadth between the eyes. Let it be remembered that when we speak of the center of the lens we mean the thickest part (if the glass be convex) and the thinnest part if the glass be concave, and not the center of the frame which holds the lens. Every eye surgeon constantly meets cases in which patients complain of discomfort in wearing spectacles, sometimes so great as to compel them to abandon the glasses ; and yet examination shows that the fault is not in the strength of the lenses, but merely in the misfit of the frame. The best way for ascertaining whether the frame is properly adapted to the individual is, of course, by wearing the glasses for a few hours. As this cannot always be done before purchasing, the buyer should, before selecting the pair of spectacles, place them in position upon his nose and look at himself in the mirror. If the spectacles are intended for distant vision, the pupils of the eyes should be seen opposite the center of the lenses ; if the glasses are meant for reading, the pupils should be situated a little outside of the center of the lenses. A frequent cause of discomfort in the use of spectacles is the innocent practice of wearing another person's glasses. One member of a family will frequently acquire a habit of using spectacles intended for the eyes of another, and will wonder that they cause so much discomfort. It should be remembered that spectacles should be fitted with the same accuracy as shoes or gloves ; indeed with more accuracy, since the eye is far more delicate and susceptible to the influence of strains than either the foot or the hand. It should be remembered that the same individual may require two pairs of spectacles for different purposes. Thus a short-sighted person will usually require weaker glasses for viewing distant objects than for reading. As the eye changes with the rest of the body in advancing years, it will become necessary to change the spectacles at intervals. A neglect to do this will, in many cases, cause much discomfort and even pain. As to the materials of the lenses themselves, the choice rests between pebble and glass. In former times the pebble (rock crystal) was much to be preferred. But in later years glass is made of a quality so much superior to that of a half century ago, that there is but little choice between the two except in one particular : this is the greater hardness of the pebble, as a result of which it is not so liable to be scratched, and may last longer. Spectacles of pebble may be wiped with a pocket handkerchief without injury, while lenses of glass should be cleaned only with a piece of wash-leather kept for the purpose. It is extremely important that spectacles be kept with care, not only to avoid scratching by contact with hard substances, but also to preserve the original shape of the frame. The pasteboard cases which are commonly employed for the purpose are rarely sufficiently stiff to resist the pressure to which they are exposed in the ordinary course of life. If it be impossible to secure the services of a professional eye-surgeon in selecting the proper lenses, the individual should bear in mind one or two points. The best way for deciding upon the strength required in the lenses is to test them by means of the types which are kept for the purpose by every dealer in optical goods. It may be said in general that a short-sighted individual should select one of the weaker glasses which enable him to accomplish the desired object, whether that be for viewing distant or near objects ; a far-sighted individual, on the contrary, may select a somewhat stronger glass for the same purpose. As a person advances in years, the eye undergoes certain changes which interfere somewhat with the performance of its functions and deprive it of some of the powers which it possessed in youth. These changes are just as natural to the eyes as the changes which occur in the skin, the hair and the bones. The eye becomes somewhat flatter, and the crystalline lens acquires a degree of hardness which renders it incapable of undergoing the same changes of form which it exhibited in early life. It will be remembered that these changes of form occur when the eye is changed from distant to near vision and conversely. When the person looks at distant objects the lens is comparatively flat ; when the eye is directed to near objects the lens is, by the action of the ciliary muscle, rendered more curved. This change in form - which is technically called the accommodation of the eye - is necessary in order that a picture of the various objects shall be accurately produced upon the retina. When the lens has become hardened and therefore less compressible than it was in early life, this power of accommodation whereby the eye can be adapted for viewing near objects is partially lost. The individual, therefore, can no longer see objects held near to the face with the same distinctness as he did twenty or thirty years previously ; though his sight for distant objects remains just as good as ever. At first he overcomes the difficulty by holding objects somewhat further from the face ; but in the course of time he is unable, even with this device, to read print of ordinary size. Hence it becomes necessary for him to employ some artificial means whereby the same effect can be produced as was formerly brought about by the change in the shape of his lens. This is accomplished by the use of a convex glass. The age at which it becomes necessary for an individual to employ glasses varies with many circumstances, though it may be regarded on the average as between 40 and 50 years of age. Some individuals, of course, are spared this necessity for a much longer time, sometimes because their eyes are subject to defects which are remedied by the change in the lens due to old age. In every case it will be well for the individual to begin with weak glasses, and change them for stronger ones as the progressing change in the eye requires. 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