EYE. 385 



CHAPTER XVII. 



Near-sightedness. Spectacles to be worn cautiously. Eye-Glaasea 

 injurious. Far-sightedness. Eye suffers with other Organs. 

 Needs Cleanliness. Bathing. Pure Air. Sufficient Light. 

 Best. 



898. THE eye is subject to very many and various derange 

 ments, which impair vision in various ways and degrees. 



Near-sightedness is one of the most common defects of vis- 

 ion. This arises from various causes. It is most frequently 

 produced by the habit of looking at very near objects ; as in 

 reading, writing, engraving, sewing, &.C., when the books, 

 papers, or work are held close to the eye. In persons so em- 

 ployed, the eye so habitually adapts its focus to these near 

 objects, that it is difficult, or even impossible, to adapt it to 

 objects at a greater distance. 



This defect may be avoided or lessened by being much 

 abroad and accustoming the eye to look at distant objects, 

 landscapes, scenery, &c., and also by holding the books or 

 the work as far from the eye as possible. 



899. In this disorder, the lenses are supposed to be too 

 round. They refract the rays too much, and concentrate 

 them, and form the image, before they reach the retina. 



Concave spectacles obviate near-sightedness. They give a dif- 

 ferent refraction to the rays, and throw the image upon the ret- 

 ina. When they are used, and especially when they are worn 

 constantly, the eye makes no effort to accommodate its focus 

 to distant objects, and remains permanently near-sighted, and 

 frequently the difficulty is increased. But if spectacles are 

 omitted as long as possible, and then used only occasionally and 

 for seeing distant objects, leaving the eye to its own resources 

 for all near and household objects, the evil would not tend to 

 increase, and the eye would enjoy a wider range of vision. 



900. Spectacles covering both eyes affect them equally, 

 and give them the same focus. But eye-glasses being used 

 for only one eye, makes that more near-sighted than the other 

 and these organs, therefore, have unequal power of vision. 



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