SOME DEFECTS OF THE EYE 



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Diagrams to be used in testing for astigmatism. 



lens is too thick, so that the image of distant objects is 

 focused in front of the retina. This tends to make one 

 squint the eye, and also to hold the object near to the 

 eye. Nearsightedness is quite common in children, and is 

 easily corrected by the use of glasses which place the focus 

 in the right place. 



Nearsightedness is remedied by means of concave eyeglass lenses. 



Farsightedness is another common defect. In farsighted- 

 ness, the eyeball is too short, or the lens too thin, and the 

 image if it could be found would fall behind the retina. 

 Hence we get a blur on the retina. This is a more diffi- 

 cult defect to recognize, because people often do not know 

 its presence until they are made aware of it by constant 

 headaches. As a person grows older, he has a tendency 

 to become farsighted. It is frequently the case that elderly 

 persons when reading need one kind of lens, and for or- 

 dinary purposes, a second lens. For this purpose a double 



