CHAPTER XLV 

 HYGIENE OF THE EYES 



277. Eyestrain. No two eyes are ever exactly alike, and 

 while the lens of the ordinary eye may be fairly satisfactory for 

 ordinary purposes, we find that very many eye lenses are not 

 adapted to doing work at close range and with small objects. 

 Now in modern times our work comes to be more and more of 

 the kind that requires the seeing of small objects, or distinguish- 

 ing small markings, at short range. The strain on the muscles 

 that adjust the eyes for far and near vision {foaising) often 

 leads to headaches and irritability, or nervousness, without the 

 person who suffers being aware of the source of his annoyance. 

 An examination of the eyes by means of special instruments easily 

 discloses any defect of the lens, and this can be corrected by 

 the use of glass lenses. 



A special defect often found in our eye lenses is that due to lack 

 of symmetry, or astigmatism. As the excessive bulging or lack of 

 curvature is usually along one line, it interferes with clear vision, 

 especially where one has to look at views in which lines are impor- 

 tant elements. Astigmatism also causes headaches and other 

 inconveniences due to eyestrain, since one unconsciously tnes to 

 bring the view into clear vision, thus straining the muscles of the eye. 



Another kind of strain results from the uneven musculature of the 

 eyes, causing the axis of one eye to turn inv^ard or outward. Squint, 

 or strabismus, in children can be remedied by a simple surgical opera- 

 tion, which evens up the tension of the muscles that move the eyeball. 

 In some cases special wedge-shaped or prismatic lenses are sufficient. 



278. Outside sources of strain. As the eye has to do with 

 perceiving light stimulations, the character and intensity of the 

 illumination are important in their effects upon the eye and 



235 



