The Special Senses 255 



vision is not changed, but the near point is removed so far 

 from the eye that near objects are no longer visible. 



Hence, when a person about forty-five years of age com- 

 plains of dim light, poor print, and tired eyes, the time has 

 come to seek the advice of an oculist. A convex lens 

 may be needed to aid the failing power to increase the con- 

 vexity of the lens, and to assist it in bringing the divergent 

 rays of light to a focus. 



-\ 398. Long or Far Sight. In "long sight," or hyperme- 

 tropia, both the near and far point of vision are concerned, 

 and there is no distinct 

 vision at any distance 

 without a strain. It is 

 a defect in the focus, 

 dependent upon the form 

 of the eyes, and often . 



* FIG. 132. Diagram illustrating the Hyper- 



existS in childhood. The metropic (Farsighted) Eye. 



axis of the eyeball is too The image P / of a point /> falls be hind the 



Short, and the foCUS falls retina in the unaccommodated eye. By 



, 11 t, t, means of a convex lens (Z,) it may be focused 



beyond the retina, WhlCh O n the retina without accommodation (dotted 



is tOO near the Cornea. lines). (To save space P is placed much 



T i -i 11 j ...I. to near the eye.) 



In childhood this strain 



may pass unnoticed, but sooner or later it manifests itself 

 by a sense of fatigue, dizziness, and a blurred and indistinct 

 vision. The remedy is in the use of convex glasses to 

 converge parallel rays of light before they enter the eye. 

 The muscles of accommodation are thus relieved of their 

 extra work. 



^, 399. Short or Near Sight. "Short sight," known as 

 myopia, is one of the commonest defects of vision. In this 

 defect the axis of the eye, or the distance between the 

 cornea and the retina, is too long and the rays of light are 

 brought to a focus in front of the retina. The tendency 



