THE HUMAN EYE 



281 



cavity containing the vitreous humor. It contains the 

 nerves of sight and is connected with the large optic 

 nerve. 



The eye is a much more perfect optical instrument than 

 the camera. The lens of the camera must be moved back 

 and forth until a distinct image is formed on the screen. 

 The lens must also be changed for various distances. 

 The eye adjusts itself almost instantly to form images of 

 near and far objects. The image formed by a normal 

 eye is much more distinct and accurate than the image 

 formed by the lens of a camera. The crystalline lens, 

 instead of moving back and 

 forth to accommodate itself 

 to various distances, simply 

 changes its shape. For near 

 objects it thickens, thus in- 

 creasing the curvature and 

 making the lens more con- 

 vex, so that it can focus the close vision Distant vision 

 rays of light on the retina. SECTION OF THE FRONT or THE EYE 



Showi 



close and distant vision. 



Ligan 



Muscle 



For distant objects the crys- Showing the change of the lens for 



talline lens is made thin 

 and less convex, so that the rays of light are not focused 

 before they get back to the retina. This process of 

 adjustment of the crystalline lens is called accommodation. 



193. How We See Objects. Nearly all objects re- 

 flect light, and this reflected light passes through the 

 cornea and is slightly refracted. The cornea acts as a 

 converging lens. The light then passes by way of the 

 pupil through the crystalline lens, which is double convex 

 and continues the refraction started by the cornea. An 

 image of the object is formed on the retina. The retina 

 contains nerves and is sensitive to this light forming the 



