THE CILIARY BODY AND LENS 



823 



changes in the lens. We have seen that the ciUary muscle is made up 

 of meridional and circular fibers. Even a casuaL study of their course 

 must show that the former are the principal factors concerned in this 

 detention, but it cannot be denied that the circular fibers are a most 

 important adjunct, because they fix the base of the ciliary body so 

 that the longitudinal fibers^ can gain a firmer hold upon this structure 

 and pull it forward. That a movement of this kind actually takes place 

 has been proved by Henson and Volker.^ Fine needles were inserted 

 through different segments of the equatorial region of the eyeball 

 which, on stimulation of the ciliary body, showed movements indica- 

 tive of a forward displacement of the choroidea. 



Fig. 429. — Diagram Illustrating the Process of Accommodation in the Human Eye. 

 C, cornea; L, lens; J, iris; CL, ciliary ligament; CB, ciliary body; Ch, choroid; R, 

 retina; *S, sclera. On near vision the ciliary muscle contracts, drawing the region B 

 nearer to region A. The tension upon the ciliary ligament being diminished thereby, 

 the lens assumes a more spherical shape, chiefly in the direction of the cornea. This 

 change is indicated in red. 



Proofs of Accommodation. — When the eye is at rest, it is accom- 

 modated for far objects. We may convince ourselves of this fact by 

 suddenly opening the eyelids after they have been held shut for a short 

 time. We then become conscious of a relaxed vision, i.e., of an accom- 

 modation for far objects, and also of a distinct effort to direct the eyes 

 to a near object. During relaxed vision, the suspensory ligaments 

 are placed under a certain tension, thereby retaining the lens in a 

 somewhat flattened condition. This may be proved by measuring 

 the anterior curvature of the lens before and after the excision of the 

 eye. It is very obvious that a lens freed from its attachments, pos- 

 sesses a more spherical outline than one still in its normal position. 

 The increased curvature of the lens, and especially that of its an- 



1 Archiv fur Ophthalm., xix, 1873, 156. 



