14 GENERAL SCIENCE 



School requirements for use of the eyes are at times ex- 

 acting but these requirements are never sufficient excuse for 

 permanent impairment of vision, nor for long-continued 

 eyestrain. Since schools do demand so much in a sustained 

 use of the eyes, it is the more necessary that all contributing 

 causes to weakened eyesight such as late hours, motion pic- 

 tures, etc., be largely avoided. Special care should be given 

 to maintain good health, and when necessary to be correctly 

 fitted with glasses. Under no circumstances should use 

 of the eyes upon difficult work, or under unfavorable con- 

 ditions, be continued after the eyes have become inflamed, 

 or have begun to ache from use, or when headache occurs 

 from eyestrain. 



SUMMARY 



While the eye as an optical instrument may be conside ed perfect 

 in its design, it is probable that relatively few people are free of defects 

 in eyesight. Most such defects are of minor character, and may 

 oftentimes be ignored. However, when the general health is impaired, 

 or when excessive and exacting use is made of the eyes, these defects 

 may become serious. Impaired eyesight is a handicap in life's activi- 

 ties and in its enjoyments. 



Intelligent care of the eyes requires a knowledge of their structure, 

 their defects, and their proper use. 



Eyestrain may be caused by dim lighting, by too glaring lights, and 

 by unequal diffusion of light. Fatigue and exhaustion of the whole 

 nervous system may follow, upsetting the equilibrium of the body 

 organism and resulting in a disordered state of the nerves and a loss 

 of mental poise. 



The small muscles whose office is to hold the crystalline lens in 

 that particular form where vision is most distinct become exhausted 

 by long-sustained close application, such as in reading fine print, in 

 continuous use of the microscope, and in doing fine sewing. This 

 strain is relieved if from time to time the eyes are used in looking at 

 other and more distant objects. Many headaches from which people 

 suffer are directly or indirectly caused by eyestrain. 



