CAUSES OF NE-RVOUS IMPAIRMENT 195 



muscle. Moderate near-sightedness adapts one to read 

 or sew with even less fatigue than if the eyes were strictty 

 normal. Nevertheless, the condition has serious disad- 

 vantages. 



If a child is at all near-sighted it may be predicted that 

 the defect will grow graver during the period of school 

 life. The actual nervous strain involved is slight, but the 

 indirect results may be deplorable. The boy who cannot 

 see well at a distance cuts a ludicrous figure in vigorous 

 outdoor sport, and, being subjected to ridicule, abandons 

 the attempt to take part in it. At first he is sensitive and 

 aggrieved. Later he convinces himself that athletics are 

 not worth while and he inclines to become a bookworm, 

 with a serious lack of physical stamina. It is fortunate 

 if he is not a conceited prig in the bargain. 



Far-sight, so far as its cause is concerned, is the exact 

 opposite of near-sight. The eyeball is not deep enough. 

 A simple experiment with a camera will serve to show that 

 such a relationship between lens and screen will result in a 

 failure to focus anything sharply, though the distance will 

 be better imaged than the foreground. By an effort such 

 as one with normal vision makes to see objects nearby, 

 the far-sighted person secures clear vision for distance; to 

 read or do other close work he must subject the accommo- 

 dation muscle to an additional strain. Thus, his eyes are 

 never at rest when they are being used at all. Yet he can 

 see quite well anything to which he turns his attention, 

 and it may be hard to make him accept the fact that he 

 has a visual defect calling for glasses. Headaches, indi- 

 gestion, and general nervous disturbances may result 

 from this condition. 



Regular astigmatism is an imperfection of the cornea or 

 anterior surface of the eye. In the majority of cases the 

 trouble is an excess of curvature up and down as com- 

 pared with that from right to left. This has been well 

 described as spoon-shaped cornea; in geometric terms 

 this important refracting surface of the eye is ellipsoid 

 instead of spheric. The purely optical consequences 



