296 



PHYSIOLOGY 



CHAP. 



was run into the ciliary bodies or near the posterior pole of the 

 eye, no movement was visible. 



/These facts together show that accommodation is brought about 

 by contraction of the ciliary muscle. Whatever the direction of 

 its fibres meridional, radial, or circular the resultant of their 

 contraction is the displacement forward towards the cornea, and 

 backward towards the axis of the eye, of all the component parts 

 of the ciliary processes. The first effect is due particularly to the 



FIG. 134. Comparative' <lrvfli>iiinrnt of the circular libri-s of the ciliary muscle in A, normal or 

 rmmetropic, B, hypermetropfc, C, myopic eye. (Fuchs.) 



meridional and radial fibres, the second to the circular fibres. 

 According to the anatomical observations of Ivanoff (1869) the 

 circular muscle-fibres are strongly developed in hypermetropic, 

 and atrophied and almost absent in myopic eyes (Fig. 134). 



This is borne out by the fact that hypermetropics are forced to 

 keep their accommodation constantly active, while this is less 

 frequently the case in emmetropia and seldom and in much less 

 degree for myopia. 



How does the contraction of the ciliary muscle effect the 

 curvature of the lens ? Various theories have been put forward, 



