796 PHYSIOLOGY. 



paralyzing the oculomotor nerve and thus the ciliary muscle, has a 

 very favorable influence by putting the affected membranes at rest. 



The suspensory ligament (zone of Zinn) is not a membrane, but 

 an agglomeration of fibers of the nature of connective tissue. They 

 originate partly at the ora serrata from the intervals between the 

 ciliary processes, and a few of them from the ciliary processes 

 themselves. 



Accompanying the act of accommodation is a contraction of the 

 pupil, which dilates when the accommodation relaxes, and a conver- 

 gence of the eyeballs due to a contraction of the internal recti. 



The range of accommodation is as follows: 



YFARI BANGKOK YKABO BANGKOK 



ACCOMMODATION ACCOMMODATION 



10 14 D. 45 3.5 



15 12 50 2.5 



20 10 55 1.75 



25 8.5 60 1. 



30 7 65 0.75 



35 5.5 70 0.25 



40 4.5 75 0. 



This table shows that the power to accommodate diminishes 

 rapidly and considerably as we become older. This is due to the 

 decreasing elasticity of the crystalline lens. The crystalline lens 

 commences early to change its physical constitution and becomes 

 more rigid, whilst our other bodily forces are in a state of progres- 

 sive development. 



In what may be regarded as the normal, or so-called emmetropic, 

 eye, the near point of accommodation is about five inches. The far 

 limit, for all practical purposes, is from 200 feet up to an infinite 

 distance. In this eye the range of distinct vision has wide latitudes. 



In the myopic, or short-sighted, eye the near point is two and 

 one-half inches from the cornea. The far limit is at a variable, but 

 not very great, distance. The range of vision in this eye is very 

 limited. In this the rays of light are brought to a focus in front 

 of the retina. 



In the hypermetropic, or far-sighted, eye rays of light coming 

 from an infinite distance are, in the passive state of the eye, brought 

 to a focus behind the retina. The near point is some distance away. 



The presbyopic, or long-sighted, eye of aged persons resembles 

 the hypermetropic eye, but differs in so far that the former is an 

 essentially defective condition of the mechanism of accommodation. 



There are two changes which occur when we accommodate for 

 near objects: one is that the pupil contracts to cut off divergent 



