THE HUMAN EYE 285 



Transportation companies do not put men who are color 

 blind in positions where safety is dependent upon recog- 

 nizing red and green lights. 



(d) Astigmatism and Headache. Astigmatism is a de- 

 fect due to improper curvature of the cornea or crystalline 

 lens so that the light is not properly focused, and imper- 

 fect images on the retina result. The muscles of the eye 

 are continually trying to adjust the parts of the eye to 

 form clear images. These overworked muscles soon be- 

 come painful. The pain is felt in and around the eyeball 

 and often in the front part of the head, where it is known 

 as headache. Headache and smarting of the eyes after 

 continued use, if the light is properly adjusted and the 

 work not more than the normal eye can stand, are signs 

 of astigmatism. 



Headache and pain in the eyes are often caused by 

 improper use of the eyes, such as reading or sewing in 

 glaring. or dim lights or by overwork in a place properly 

 lighted. Reading ordinary print on a moving train or 

 electric car soon produces pain in the eyes for most 

 people, because of the continuous use of the muscles in 

 keeping the parts adjusted and the eye directed to a defi- 

 nite spot on the shaking paper. 



The remedy for astigmatism is to wear glasses of the 

 proper kind, prepared under the direction of a well- trained 

 oculist. The pain in the eyes and headache caused by 

 astigmatism will be relieved if the proper shaped lenses 

 are secured. Sometimes astigmatism may be perma- 

 nently cured if the eyes are properly treated and cared 

 for. 



195. Care of the Eyes. Numerous investigations have 

 shown that most children are born with good eyes, and 

 that the eyes become injured through improper use. 



