NEAR- AND FAR-SIGHT 



419 



not become rounded when it 

 is released. We are, therefore, 

 likely to lose the power of accom- 

 modation. 



418. Near- and Far-Sight; 

 Care of the Eyes. When a 

 normal eye is at rest, it is 

 in focus for distant objects. 

 For close objects, accommo- 

 dation must be used. A 

 " near-sighted " eye (Fig. 

 302) cannot see objects dis- 

 tinctly at more than about 

 10 inches' distance; when 

 the object is at a greater 

 distance, the focus is formed 

 in front of the retina. Hence 

 the light rays have crossed 

 before reaching the retina, 

 and the image is blurred. 

 The remedy for short- 

 sightedness is a concave lens 

 (cf. 178) of the right cur- 

 vature. This throws the 

 image farther back, upon the 

 retina. 



In far-sighted vision the 

 object to be seen must be 

 more than 10 inches away; 

 otherwise the image will fall 

 behind the retina. Of course 



Normal 



Near Sight 



Far Sight 



Fig. 302. 



Diagram of a Normal Eye, a Near- 

 Sighted Eye, and a Far-Sighted Eye. 

 The near-sighted eye needs a concave 

 lens ; the far-sighted eye, a convex lens. 

 The dotted curved lines show where the 

 retina would be, if the defective eye were 

 normal. The dotted straight lines show 

 how the light rays are brought to a 

 focus by the proper eye-glasses. 



