48 SCIENCE PROGRESS 



only with bright light — using that term in its broadest sense — 

 but also with other forces, mechanical, electrolytic and so on. 

 The results are correspondingly complex. In addition to 

 changes in the retina, inflammation or atrophy of the optic 

 nerve, inflammation of the vascular coats of the eye (iris, ciliary 

 body, and choroid), etc., a very large proportion of the cases 

 show the development of cataract, i.e. opacification of the 

 crystalline lens. It is improbable that the cataract produced in 

 this manner is due merely to the effects of exposure to the 

 sudden intense light. It is more likely to be caused by the 

 concussion of the stroke, being thus brought into line with other 

 well-known examples of concussion or traumatic cataract. Some 

 of the changes in the eye are, however, almost certainly due to 

 light and are exactly comparable with those found in short- 

 circuiting an electric main. 



There is another condition under which, after exposure to 

 bright light and heat, cataract develops — viz. amongst glass- 

 workers. The cataract in these cases is of a very characteristic 

 type, the opacity being limited in the early stages to a small 

 circular area in the posterior part of the crystalline lens. The 

 men who most suffer from this disease are elderly men who 

 have pursued the trade from boyhood. They have generally 

 passed through all the stages in the manufacture — usually of 

 ordinary bottles such as are used for beer, etc. Most of them 

 are expert workmen who are engaged in "finishing" bottles, 

 i.e. putting a ring of molten glass round the mouth of the bottle. 

 The performance of this operation demands keeping the eyes 

 fixed almost continuously upon the molten glass, either in the 

 process of taking the requisite amount of "metal" out of the 

 furnace or in fashioning the ring. Whether this form of cataract 

 is caused by the exposure to the intense light or to heat or 

 other concomitant factors is at present unknown. It is occupy- 

 ing the attention of a committee of the Royal Society which has 

 been appointed for the elucidation of the problem. 



The conditions hitherto considered of affection of the eyes 

 after exposure to bright light have dealt only with serious 

 defects of vision resulting from disease of the deeper structures. 

 The more superficial parts are not infrequently affected, fortu- 

 nately with less disastrous consequences. Snow-blindness is an 

 example of this kind : in this case, after exposure to the bright 

 light reflected from the surface of the snow, the superficial parts 



