298 



PHYSIOLOGY 



CHAP. 



and short ciliary nerves of cats and rabbits no longer produces any 

 effect of accommodation (Langley and Anderson, 1892). As it 

 has been proved that nicotine paralyses the nerve-cells of ganglia, 

 while it leaves the excitability of the fibres unaffected, this ex- 

 periment proves that the cells of the ciliary ganglion are inter- 

 calated in the peripheral fibres that innervate the ciliary muscle 

 (Vol. III. p. 367 ff.). 



In normal eyes the innervation of the ciliary muscle is always 

 synchronous and equal in both eyes, and extends to every part 

 of the muscle. The question whether under special conditions 

 unequal or unequally extensive accommodation in the two eyes is 

 possible is of great practical interest, because it is conceivable that 

 such an unequal innervation of the two sides might compensate 

 a different refractive power in the two eyes. Schneller and 

 A. E. Tick believed it possible to read very small writing with 



FIG. 135. Diagram of anterior part of the eye, accommodated on the left for distant vision, on 

 the right for near vision. (Luciani.) The figure shows that in accommodation the ciliary 

 muscle thickens, the ciliary processes advance and approach the equator of the lens without 

 increasing in size, the anterior and to some extent the posterior curvature of the lens 

 increases, the sphincter of the iris contracts, the iris angle becomes more obtuse, and the 

 anterior chamber is reduced in size. 



both eyes, even when a plus or minus lens of more than 1 D. 

 was held in front of one eye. But the later researches of Hess 

 and Neumann (1892) make this hypothesis untenable. They 

 found that normal eyes are notable by unequal accommodation to 

 compensate an artificial difference in refraction amounting only 

 to 0-12 D. And on the other hand, recent ophthalmic literature 

 affords sufficient grounds for the belief that in cases of unequal 

 refraction of the two eyes (cmisometropia), and also in cases of 

 strabismus and unilateral blindness, the accommodation in both 

 eyes is equal. 



The statement of Morat and Doyon (1891) that the sympa- 

 thetic inhibits accommodation and serves to adapt the eye to 

 distant vision has been contradicted by all the subsequent 

 observers who have controlled it (Langley and Anderson, Hess 

 and Heine, Eomer and Dufour). 



