260 IMPORTANCE OF OUR EYES 



The eye is able to adjust itself to different amounts of light, 

 within rather wide limits, without harm. In order to avoid 



straining the eye, it 

 is necessary to have 

 enough light. Much 

 harm is sometimes 

 done when we are 

 young by trying to 



How does the eye adjust itself to different intensities read hi insufficient 

 of light ? T . , . , 



light ; just as much 



harm has been done by looking into a blinding light, or 

 trying to look at the sun, as some youngsters do at times 

 to " stunt " each other. 



Some defects of the eye. Although the eye is a wonder- 

 ful piece of mechanism, it has several common defects. 

 Fortunately, due to a study of the eye and of the science 

 called optics, we are now able to remedy most of these de- 

 fects very easily, especially by the use of glasses. It is 

 estimated that one person in every four has some defect 

 in vision. Nearly twenty-five per cent of the school chil- 

 dren in Massachusetts and over thirty per cent of the 

 school children in New York have eye trouble of some 

 kind. The most common defect of the eye is astigmatism. 

 This is usually due to a slight uneven curvature of the 

 cornea, or the lens. It can easily be discovered by use of 

 the diagram on page 26 1 . Look at either of the figures with 

 one eye closed. If some of the lines appear blurred or 

 thicker than others astigmatism is present and should be 

 corrected with glasses, as this defect is a frequent cause 

 of headache. 



The next most common defect is nearsightedness. In 

 this case the eyeball is too long from front to back, or the 



