262 IMPORTANCE OF OUR EYES 



glass, called bifocal, combining the two lenses in one is 

 often used. 



Farsightedness is remedied by means of convex eyeglass lenses. 



Testing of eye defects. A very simple exercise for 

 testing most eye defects is given in the following labora- 

 tory experiment. 1 



Experiment. To test my own eyes for defects. 



Y F E V 



A. Test for Farsightedness 



Method: Using the Snellen test cards, locate the finest line that can 

 be read at a distance of 20 feet. Test each eye separately, covering the 



eye not in use with 

 a piece of cardboard. 

 Then place a pair of 



How far away can you read these letters? Measure s P ectacles Wlth a 5 

 the distance. Twenty feet is a test for the normal plus diopter lens be- 

 fore the eyes. If as 



fine or a finer line can now be read, then farsightedness is present and an 

 oculist should be consulted, especially if headaches or other symptoms 

 of eye defects are present. Farsightedness is one of the most frequent 

 causes of eyestrain and is hard to detect because the eyesight seems 

 .so good. 



B. Test for Nearsightedness 



Method: Use the above-mentioned charts. Determine the finest type 

 you can read at a distance of 20 feet. If it is larger than the 20/20 

 line, then your vision is defective and you should probably consult 

 an oculist, especially if you have any symptoms of eyestrain. 



1 This test was prepared by Dr. Lucius J. Mason of the Department of 

 Biology, DeWitt Clinton High School, New York. 



