EFFECTS OF BRIGHT LIGHT UPON THE EYES 49 



of the eye become intensely inflamed. The part most affected is 

 the conjunctiva or mucous membrane which covers the inner 

 surfaces of the lids and is reflected from them on to the outer 

 parts of the eyeball. The inflammation sets up a most severe 

 irritation, just as if sand or dust were present in the eyes. 

 As a result the lids are tightly closed and the least attempt to 

 open them is accompanied by pain and violent spasm. This 

 condition is generally known as "photophobia" but it is very 

 doubtful whether the dread of light plays an}' part in its 

 production. 



Almost identical with snow-blindness is the condition called 

 " ophthalmia electrica." It occurs after prolonged exposure of 

 the eyes to the naked arc light, to other forms of electric light, to 

 the light emitted by mercury vapour lamps and so on. There 

 is the same inflammation of the conjunctiva and spasm of the 

 lids (blepharospasm). Sometimes, as also in snow-blindness, 

 the cornea or clear anterior membrane of the eye which is so 

 important for vision shows excoriations of the surface and even 

 deeper parts may be affected, hyperaemia or actual inflammation 

 of the iris, etc., sometimes occurring. 



In these various causes which are productive of injury to 

 the eyes and sight it is obvious that bright light, though itself 

 complex, is not the sole factor to be considered. Thus it is 

 fairly certain that light plays a relatively small part in the 

 development of lightning cataract, for this disease is seldom if 

 ever present in cases of short-circuiting, unless indeed an actual 

 electric shock has been received by the patient. If we analyse 

 the physical factors we shall find that in some, as in glass- 

 workers' cataract, there is also intense heat. In almost all 

 various forms of radiant energy are at work, not only all the 

 waves of the visible spectrum but also the very active chemical 

 or actinic ultra-violet rays. It is not impossible that in some 

 cases X-rays or radium emanations may play a part. 



In the complete elucidation of the subject it is necessary 

 to determine not only what force is the actual cause of the 

 lesion but also whether it acts directly on the structure injured 

 or affects it secondarily by interfering with its nutrition, either 

 by interfering with the normal functions of other structures of 

 the eye or by affecting the general bodily health. In most 

 cases the exact method of action is very imperfectly understood 

 and consequently we are unable to apply any very rational or 



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