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Mr. Ernest Clarke 



[June 0, 



It must be borne in mind that although this hardening process 

 affects all lenses, no matter what the refraction may be, it is naturally 

 not manifested in all alike ; for instance, the myope of 5 D whose 

 far point is 20 cms. from the eye will be able to read small print to 

 the end of life without glasses, whereas the hypermetrope of 5 D when 

 he reaches the age of thirty-five has to use up all his accommodative 

 power to correct his defect, and so must have convex glasses for 

 near work. 



TTe see, then, that in the normal individual, or those made 

 normal by the correction of the refi'active error, the average age for 

 the onset of presbyopia is about forty-eight, and yet if we look at 

 the table (Fig. 2) we see an enormous variation from this average. 

 Take the line of age fifty : we see one individual has 6 D accommo- 

 dative power, whereas another has only 1 D. What is the cause of 

 this variation ? 



Sir "William Arbuthnot Lane has shown that one of the commonest 

 causes of premature senility is intestinal toxaemia, and I have shown 

 •elsewhere that the lens is perhaps the most delicate index of this 

 degeneration. 



In making a large number of investigations I found that if the 

 person looked older than his years, his lens invariably showed that 

 he possessed less accommodative power than the average — in other 

 words, the lens was sclerosed more than it should be. It is common 

 knowledge that the average man of fifty looks fifty, and acts as if 

 fifty, but many aged fifty look sixty-five, and to all intents and 

 purposes are sixty-five, whereas others may look only thirty-eight 

 or forty. 



Another cause of premature senility, as evidenced in lessened 

 accommodative power, is eyestrain. This is probably due not only 

 to loss of nerve energy, but also, to a certain extent, to degenerative 

 changes caused by the unequal contraction of the ciliary muscle, 

 which I have already referred to. 



