REFRACTION IN THE EYE 477 



lens moves forward in accommodation (Helm- 

 holtz). 



2. Place the diaphragm with L-shaped aper- 

 ture in the lantern. In a dark room place the 

 lantern in front and to the inner side of the 

 subject's eye, so that the rays shall make an angle 

 of about 40 with the visual axis of the eye 

 directed forwards. Let the observer's eye be in 

 a corresponding position to the outer side of the 

 subject's eye. In the visual axis of the subject's 

 eye place an object at the near point and one at 

 the far point (six metres). Let the subject 

 accommodate for the far point. 



Note the sharp, very bright, upright image 

 reflected from the cornea, the indistinct, faint, 

 upright, slightly larger image from the convex 

 anterior surface of the crystalline lens, and lastly, 

 the sharper, faint, inverted, small image reflected 

 from the concave posterior surface of the lens. 1 

 The image from the anterior surface of the lens 

 lies apparently 8-12 mm. behind the pupil, and 

 therefore disappears behind the border of the 

 iris upon slight changes in the position of the 

 light or the observer's eye. The image from 

 the posterior surface lies apparently about 1 mm. 



1 These images may be magnified with advantage by looking 

 at them through the lens of 7.5 cm. focal distance furnished 

 with the ophthalmoscope. 



