VISION 501 



COLOK BLINDNESS 



The three large skeins show the test colors. 



1. Light Green. Palest (lightest) shade of 

 very pure green, neither yellow-green nor 

 blue-green to the normal eye. Light green is 

 chosen because, according to the Young-Helm- 

 holtz theory, it is the whitest of the colors of 

 the spectrum, and, consequently, is most easily 

 confused with gray. Light shades are employed 

 because it is difficult to distinguish between 

 strongly illuminated shades. 



2. Purple (Rose). A skein midway between 

 lightest and darkest purple. Chosen because 

 purple combines two fundamental colors which 

 are normally never confounded. 



3. Red. A vivid, slightly yellowish red. 

 Chosen because it represents the color-group in 

 which red (orange) and violet (blue) are com- 

 bined in nearly equal proportions. 



Method of Examination and Diagnosis. Place 

 the Berlin worsteds on the white cloth in which 

 they are wrapped. They should be well mixed, 

 and not spread out too much. Lay a skein of 

 the first test-color in a well-lighted position two 

 or three feet from the group. Inform the person 

 examined : 



