2 5 6 



Life and Health 



to shortsightedness exists in many cases at birth, and is 

 largely hereditary. It is alarmingly common with those 



who make a severe 

 demand upon the eyes. 



During childhood there 

 is a marked increase of 

 nearsightedness. The 

 results of imprudence and 



FIG. 133. Diagram illustrating the 

 Myopic (Nearsighted) Eye. 



abuse, in matters of eye- 

 sight, are so disastrous, 



The image P' of a distant point P falls in especially during School 



front of the retina even without accommo- Rf ^ the tion f 



dation. By means of a concave lens (/,) 



the image may be made to fall on the retina short sight becomes One 



(dotted lines). (To save space / is placed of much importance, 

 much too near the eye.) . r 



Nearsightedness often 



demands skillful advice and careful treatment. Concave 

 glasses, properly adjusted to meet the conditions of the 

 eyes, may be needed. 



Experiment 117. To note the shadows cast upon the retina by 

 opaque matters in the vitreous humor (popularly known as floating 

 specks, or gossamer threads}, look through a small pinhole in a card 

 at a bright light covered by a ground-glass shade. 



-/Experiment 118. To illustrate accommodation. Standing near a 

 source of light, close one eye, hold up both forefingers not quite in a 

 line, keeping one finger about six or seven inches from the other eye, 

 and the other forefinger about sixteen to eighteen inches from the eye. 

 Look at the near finger ; a distinct image is obtained of it, while the 

 far one is blurred or indistinct. Look at the far image ; it becomes 

 distinct, while the near one becomes blurred. Observe that in accom- 

 modating for the near object, one is conscious of a distinct effort. 



v 400. Astigmatism. There is an optical condition of the 

 eye known as astigmatism, in which the cornea is usually at 

 fault. In this defect of vision the curvature of the cornea 



