Chap. XX] 



SUMMARY 



441 



Refraction — Bending or deviation in the course of rays of light, in pass- 

 ing obUquely from one transparent medium into another of 

 different density. 



Accommodation — AbiUty o£ the eye to adjust itself so that it can see 

 objects at varying distances. 



Conditions 

 that affect 

 Accommo- 

 dation 



Hypermetropia 



Myopia 



Presbyopia 



Astigmatism 



Far-sightedness. 



Cause — Rays of hght do not con- 

 verge soon enough. 



Xear-sightedness. 



Cause — Rays of light converge too 

 soon. 



Defective condition of accommodation 

 in which distant objects are seen 

 distinctly, but near objects are in- 

 distinct. 



Condition in which the different merid- 

 ians of the eye are not equally 

 convex. Interferes with distinct 



