KEFRACTIOX IN THE EYE 473 



MECHANISM OF ACCOMMODATION 



Narrowing of Pupil. 1. Watch the pupil while 

 the subject accommodates first for a distant and 

 then for a near object. 



In accommodation for near objects the pupil 

 contracts. 



2. Hold a pencil about thirty centimetres in 

 front of one eye. Close the other eye. The 

 pencil is seen clearly. Move the pencil towards 



Pig. 66. 



the eye until its image becomes indistinct from 

 dispersion circles. Now observe the pencil 

 through a pin-hole in a card placed in front 

 of the pupil. 



The image is sharper. The size of the dis- 

 persion circles is diminished by making the 

 aperture smaller and thus cutting off the rays 



