THE EYE 



385 



difference in curvature of the surfaces of the cornea 

 or crystalline lens. It is corrected by lenses so ground 

 as to correct the particular defects present in a given 

 eye. 



Whenever defects in focusing are present, particularly 

 in astigmatism, extra work is thrown on the ciliary muscle 

 as well as the muscles that move the eyeballs. The result 

 is frequently to induce a condition, known as muscle iveak- 

 ness, which renders it difficult to use the eyes. Even after 

 the defect in focusing has been remedied, the muscles re- 

 cover slowly and must be used with care. For this reason 

 glasses should be fitted by a competent oculist 1 as soon 

 as a defect is known to exist. When one is unduly nerv- 

 ous, or suffers from headache, the eyes should be examined 

 for defects in focusing (page 326). 



Eye Strain and Disease. The extra work thrown upon 

 the nervous system through seeing with defective eyes, 

 especially in reading and other close work, is now recog- 

 nized as an important cause of disease. Through the tax 

 made upon the nervous system by the eyes, there may be 

 left an insufficient amount of nervous energy for the 

 proper running of the vital processes. As a result there 

 is a decline of the health. Ample proof that eye strain 

 interferes with the vital processes and causes ill health, is 

 found in the improvements that result when, by means of 

 glasses, this is relieved. 



The Eyes of School Children. School children often 

 suffer from defects of vision which render close work bur- 

 densome, and cause headache, general nervousness, and 

 disease. Furthermore, the visual defects may be unknown 

 both to themselves and to their parents. Pupils showing 

 indications of eye-strain should be examined by an oculist, 



1 An oculist is a physician who specializes in diseases of the eye. 



