348 



GENERAL SCIENCE 



the person who can read only the line marked forty feet is seriously 

 defective, and if the line marked forty feet cannot be read, the 

 trouble may be considered serious. Headaches, swollen, crusted, or 

 reddened eyelids, styes, inflamed eyeballs, squinting, blinking, 

 twitching of eyelids, and wrinkling of the forehead indicate pos- 

 sible eye strain. 



If a person is found to be near sighted, or suffering from astigma- 

 tism, consult the eye specialist immediately. 



11 



HORIZONTAL 



The above chart is used to test 

 extreme cases of astigmatism. It 

 is not always an absolutely re- 

 liable test, however. 



Observe each letter and each radi- 

 ating line. If any of the letters 

 or lines look darker than others, 

 astigmatism is present. 



SO 9 



III 



Itllull 



135' 



105 120' 



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il'"it "//y/ 



II h '////; 

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60 



75 



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X VAY 



165 



Astigmatism. This defect of the eye is caused by the lens or 

 cornea being unsymmetrical; that is, parts of the lens or cornea are 

 so flattened as to cause some rays of light to be slightly out of focus 

 while the eye is engaged in trying to produce a perfect image. This 

 effort to supply power to the nerves and muscles causes twitching 

 of the facial muscles of the eyelids. 



Test for Astigmatism. To test the eyes for astigmatism hold 

 the diagram containing the radiating lines from two to three feet 



