260 



REFRACTION 



quence near objects look blurred. Farsightedness can be 

 remedied by convex glasses, since they bend the light and bring 

 it to a closer focus. Convex glasses, by bending the rays and 



FIG. 132. The farsighted eye. The defect is remedied by convex glasses. 



bringing them to a nearer focus, overbalance a short eyeball 

 with its tendency to focus objects behind the retina. 



A nearsighted person is one who cannot see objects unless 

 they are close to the eye. The eyeball of a nearsighted per- 

 son is very wide, and the retina is too far away from the crys- 

 talline lens. Far objects are brought to a focus in front of the 

 retina instead of on it, and hence are not visible. Even though 

 the muscles of accommodation do their best to pull out and 

 flatten the lens, the rays are not separated sufficiently to focus 

 as far back as the retina. In consequence objects look blurred, 

 Nearsightedness can be remedied by wearing concave glasses v 



FIG. 133. The nearsighted eye. The defect is remedied by concave glasses. 



since they separate the light and move the focus farther away. 

 Concave glasses, by separating the rays and making the focus 

 more distant, overbalance a wide eyeball with its tendency to 

 focus objects in front of the retina. 



Headache and eyes. Ordinarily the muscles of accommo- 

 dation adjust themselves easily and quickly; if, however, they 



