420 THE NERVES AND THE SENSE ORGANS 



this is impossible, since the retina is opaque; but the 

 image on the retina is blurred, because the light is not 

 yet at a focus. The crystalline lens prevents far-sight, 

 if it has the power of accommodation. When this 

 power is gone, convex lenses are needed to help the 

 crystalline lens, and to make accommodation unne- 

 cessary. 



Astigmatism (a-sttg'-mat-ism) is a defect of vision that is due to a 

 lack of sufficient curving, or a flatness, in some part of the cornea or 

 crystalline lens. The muscles of the eye keep trying to adjust the eye 

 and the lens so as to make a distinct image, and become worn out in 

 the attempt. Glasses for astigmatic eyes are made to correct the 

 particular trouble of each eye, and are of no use unless an expert 

 oculist fits them. There are few errors of vision that the oculist cannot 

 correct, and we should consult him at once if we have any difficulty 

 with our eyesight. Poor vision causes a constant strain upon the 

 eyes, with headaches, inflammation of the eyes, and nervousness. 

 Wonderful improvement in the general health often follows the 

 wearing of the right glasses, and the relieving of the eye from strain. 

 The eye is so delicate that if it is upset the whole nervous system 

 feels the effect. 



Care of the Eyes. We should never rub the eyes with 

 the fingers unless we are certain that the fingers are clean; 

 otherwise the eyes may become infected. We should 

 read only in a good light, but the light should not be too 

 bright, and should not be reflected directly to the eye. 

 Sunlight is too bright for reading. If we read or study by 

 lamplight, either our eyes or the lamp should be shaded, 

 best by a green shade. We ought not to read in a moving 

 train or street car for more than a little while. The jar- 

 ring of the car causes the book to shake, and the eye is 



