532 



VISION 



The whole anatomical structure of the eye indicates that the ciliary muscle 

 must in some way participate in bringing about the change in the curvature 

 of the lens. But views differ considerably as to the way in which this takes 

 place. 



In a meridional section of the eye, the ciliary muscle (Fig. 227) fills up 

 a triangular field in the ciliary body. It constitutes therefore in the whole 

 circumference of the eyeball a circular three-sided, prismatic band, which, as 



15 



FIG. 227. Meridional section through the ciliary body of a human eye, after Schwalbe. 1, cor- 

 nea ; 2, membrane of Descemet ; 3, sclerotic coat ; 4, Schlemm's canal ; 8, stroma of the iris ; 9, 

 pigment epithelium of the iris;.Z0, inner connective-tissue layer of the ciliary body, continu- 

 ous with the connective-tissue framework of the ciliary process; 13, meridional fibers of the 

 ciliary muscles; 14, radial fibers of the ciliary muscle; 15, circular muscle of Miiller; 16, circu- 

 lar muscle fibers of the inner surface of the ciliary body ; 17, choroid coat. 



the figure shows, is often interlaced with strands of connective tissue. Iwa- 

 noff distinguishes three kinds of muscular fibers according to their direction, 

 namely, (1) meridional fibers running from the sclerotic fold, (3', Fig. 227) 

 backward to the boundary of the true choroid coat; (2) radial fibers extend- 

 ing from the lamellae beneath Schlemm's canal to the whole inner face of the 

 triangle ; and ( 3 ) the circular fibers, the strongest bundles of which run along 

 the short anterior face of the triangle and in its inner anterior angle (15, Fig. 

 227). Besides, all the radial bundles bend around on the inner face of the 

 muscle, taking a circular direction and forming in this way a more or less 

 extensive circular layer. 



According to Iwanoff the ring* muscle appears to be developed to differ- 

 ent degrees in eyes having different static refractive powers; thus in myopic 

 eyes it is almost entirely wanting, while in hypermetropic eyes it is strongly 

 developed and amounts to about one-third of the whole ciliary muscle. 



The lens rests in a concavity in the anterior face of the vitreous body and 

 is attached by an anterior prolongation of the hyaloid membrane known as 



