THE SENSES 



When distant objects are looked at the lens becomes flatter 

 as a result of the contraction of the suspensory ligament, 

 which contraction is a consequence of the relaxation of the 

 ciliary muscle. Accommodation for distant objects seems 

 a passive process entirely. 



The ciliary muscle is the "muscle of accommodation." 



The contraction of the pupil for near objects is not, prop- 

 erly speaking, a part of accommodation. 



Then, granting special sensibility to the retina and optic 

 nerve the formation and appreciation of an image is simple. 

 Rays of light having passed through the cornea and aqueous 

 humor are admitted by the pupil to pass through the lens and 

 vitreous humor. By all these objects they are refracted so 

 that they cross each other and fall upon the retina, producing 

 an inverted image there. The size of the pupil, other things 

 being equal, is regulated by the intensity of the light, the 

 opening being contracted to admit less when the light is 

 strong. 



Myopia, Hyperopia and Presbyopia. Sometimes the an- 

 tero-posterior diameter of the eye-ball is too long and the 

 rays of light are brought to a focus in front of the retina. 

 Such a condition is known as myopia; the person will be 

 near-sighted. He brings objects near his eyes so that the 

 rays may have a greater divergence and thus be focused far- 

 ther back. Or the rays may be scattered by placing concave 

 lenses before the eyes. Sometimes, too, the antero-posterior 

 diameter may be too short and the rays come to a focus be- 

 hind the retina. Such a condition is known as hyperopia; 

 the person will be far-sighted. He holds objects far away 

 from his eyes that the rays from them may strike the ball 

 with less divergence and thus be focused farther forward. 

 Or the same end may be accomplished by placing convex 

 lenses before the eyes. In old age the lens becomes flattened 

 and accommodates itself less easily. This tends to focus light 

 behind the retina and objects have to be held far away from 



