23 HYGIENE OP THE EYES. 



blurred and indistinct. The opposite defect is long-sight. 

 In those who suffer from it, the eyeball is so flat that the 

 lens cannot focus on the retina rays of light coming 

 from a near object (C, Fig. 57). 



FIG. 57. Diagram illustrating the path of parallel rays of light after entering 

 a healthy, well-shaped eye (A), a short-sighted eye (.5), and a long-sighted eye (C). 



9. Hygiene of the Eyes. Looking directly at very 

 bright objects, as the sun or an electric lamp, dazzles 

 and injures the eyes; so does sudden change from dark- 

 ness to light. On first waking, the eyes should be some- 

 what gradually accustomed to bright light. The ill 

 effects of such changes are much less serious than the 

 harm that may be done by using the eyes when there is 

 not enough light to see clearly. Frequent reading or 



9. What is the effect on the eyes of looking at very bright lights ? 

 Why should they be gradually accustomed to light after sleeping? 

 What is even more injurious to the eyes than sudden changes from 



