THE EYE 



349 



away. Astigmatism is present if some of the lines are brighter and 

 more distinct than others. The specialist will be able to tell whether 



FIG. 228. Astigmatism. A part of the lens or cornea of the eye is defective, 

 causing the rays of light, H, H, to meet beyond the retina. Why do the 

 rays of light, V, V, meet on the retina? 



the person is suffering from compound or a simple form of astig- 

 matism. 



Evidence of Eye Strain. Headaches which occur regularly, 

 becoming worse as the day advances, are a strong evidence of defec- 

 tive eyes. Often a feeling of nausea and a sense of fatigue after a 

 strenuous day's " close " work are due to eye strain. 



FIG. 229. Different kinds of 



The cause of the agonizing headaches, dyspepsia, loss of appetite, 

 and insomnia from which so many school boys and girls suffer may 

 often be traced to diseases of the eyes. 



The strain and fatigue of the eye muscles is communicated to 

 the centers governing the pneumogastric nerve, which has a great 

 influence over the stomach and digestion. 



Cause of Seasickness. Sometimes people are made sick by the 

 constant changing of the focus of vision caused by looking at the 

 horizon over the side of a vessel that is rising and sinking with the 



