104 



BIOPHYSICAL CHARACTERISTICS OF THE EYE 



in solution, for a 1.1068 per cent salt solution at 25° C has an index of 

 refraction 1.3344. The axial thickness of the anterior chamber con- 

 taining the aqueous humor is about 3.6 mm. 



Temporal 



Tendon 



w-rectus oculi 

 lateralis 



Posterior surface 

 of iris pigment layer 



Sclera 

 Chorioidea 



Stratum 



pigmenti 



retinae 



m-rectus oculi 

 medialis 



Nasal 



Fig. Ill— 3. Schematic horizontal meridional section of eyeball. 



Crystalline Lens 



The contents of the eyeball are partitioned by the iris into two parts. 

 In front of the iris lies the anterior chamber whose outer boundary is 

 the cornea. Behind the iris is the firm, convex crystalline lens. 



This lens is a transparent biconvex plastic mass enclosed in an elastic 

 membrane, called the capsule (Fig. III-4). The elastic property of 

 this capsular membrane accounts for the change in shape of the lens. 

 This is shown by the fact that, when the capsule is pierced, the semi- 

 solid lens substance is forced out as a blister; and, if the capsule is 

 removed, the lens does not return to its original shape. 



The capsule varies in thickness. It is very thin at the posterior sur- 

 face near its vertex, but thicker at its anterior pole. It increases in 

 thickness toward the periphery of the lens. The result is that the inter- 



