REFRACTION IN THE EYE 445 



CARDINAL POINTS OF THE CRYSTALLINE LENS 

 (SYSTEM B) 



Construction Drawing of System B. When 

 the lens is accommodated for distant vision the 

 radius of the anterior surface is about 10 mm., 

 the radius of the posterior surface about 6 mm. ; 

 the thickness at the principal axis 3.6 mm. The 

 index of refraction of the lens is 1.4371. The in- 

 dex of the aqueous and vitreous humors is 1.3365. 



Beneath the construction drawing of the 

 cardinal points of the cornea (System A) draw 

 a horizontal line parallel to the optical axis 

 of the cornea. This line will serve as the 

 optical axis of the lens. From the intersection 

 of the cornea with its optical axis let fall a 

 perpendicular to the optical axis of the lens. 



The anterior surface of the lens intersects the 

 optical axis 3.6 mm. posterior to the cornea. 

 The radius of the anterior surface of the lens is 

 10 mm. Find therefore on the optical axis a 

 point 3.6 + 10 = 13.6 mm. behind the cornea. 

 From this point as a centre describe an arc with 

 a radius of 10 mm. that shall intersect the optical 

 axis 3.6 mm. behind the cornea. A segment of 

 this arc will represent the anterior surface of 

 the lens. 



