nearsightedistess and faesightedness 467 



Hygiene of the Eyes. 



The eyes are extremely sensitive organs, and their satis- 

 factory working depends upon the health of the general sys- 

 tem. Poor circulation, which results in lack of nourishment, 

 as in disease, often affects the eyes. Biliousness often ren- 

 ders the eyeballs yellow and sore. Nervous diseases also 

 disturb their functions. Filth and dirt or rubbing the eyes 

 with dirty hands may often cause diseases of the eyebaU 

 and lids. To remove the dirt which accumulates, the eyes 

 should be bathed as carefully as other parts of the body. 

 For this purpose warm or tepid water is better than cold. 



Reading in a strong light or dim light or overuse tends 

 to strain the muscles which operate the lenses and eyeballs 

 and thus weaken them. Flickering light especially re- 

 quires overexertion on the part of these muscles in accom- 

 modation and should be avoided. Often the eye is defective 

 in structure, and unless this defect be corrected may react 

 upon other parts of the system producing severe headaches 

 and other nervous troubles. 



All e}^e troubles may be classed as eye defects or eye 

 diseases. The most common defects of the eye are near- 

 sightedness, farsightedness, and astigmatism. 



Nearsightedness and farsightedness. — In a normal eye images 

 of both near and distant objects are, through the accommodation 

 of the lens, projected exactly upon the surface of the retina. When, 

 however, the eyeball is too short or too long, that is, abnormal in 

 shape, the image instead of being formed on the retina is pro- 

 jected 'either in front or back of it, and the result upon the 

 vision is a blurring often accompanied by headache. When the 

 image is formed in front of the retina the defect is called near- 

 sightedness (myopia). The defect may be corrected by the 

 use of spectacles made with divergent lenses, which spread the 



