EFFECTS OF RADIANT ENERGY ON THE EYE. 765 



ideal light is cloud light or skylight, used the most accurate instruments 

 available in the laboratory of C. Zeiss, in Jena, to measure the percent- 

 age absorptive power at different points in the spectrum, of various 

 glasses. These glasses were all found to be inferior to opal and milk 

 glass for the purpose of enclosing strong arc lights to produce a spec- 

 trum most nearly approaching in quality and quantity, the spectrum 

 obtained from sky light. 



Recently (1912) Martin ^^^ has verified some of the results of 

 Widmark, Hess, and Romer, while Carl Behr ^"^ has reported some 

 very interesting functional disturbances of light adaption power of 

 the eyes in patients working by artificial light. These results will 

 later be taken up more in detail. 



Having thus rapidly traced the important steps in the progressive 

 development of the knowledge of ultra violet light in relation to the 

 eye, the mass of findings may doubtless be rendered much more 

 available by considering them separately and in more detail with 

 reference to the A'arious parts of the eye. 



The Outer Eye. — Photophthalmia, Vernal Catarrh. 



Probably ophthalmologists have experienced less difficulty in reach- 

 ing definite conclusions, concerning the condition called ophthalmia 

 electrica or photophthalmia (Parsons ^^^), than with any of the other 

 effects of ultra violet light. As to the symptom complex little has 

 been added since the first report in 1858 (cf . page 635) of Charcot ®^ 

 and the later observations of Martin ^^^ and Nodier ^^^ in 1881, shortly 

 after the general introduction of the electric arc for lighting and 

 furnaces, (in 1879 and 1880). The workmen most exposed to these 

 arcs, particularly the furnace arc, began to complain of symptoms 

 that we now know to be due to photophthalmia (see page 634). 

 In a week the eyes were practically normal. The affection of the sur- 

 rounding skin known as dermatitis electrica was not unlike that of 

 sunburning of severe grade except in its origin. As in sunburn, a 

 tanning was notable after the inflammation had subsided, for several 

 weeks. Although retinal changes were seldom noted with the oph- 

 thalmoscope, functional disturbances were observed such as temporary 

 blindness or scotomata, floating spots of red, yellow or blue or occasion- 

 ally erythropsia, or red vision. Therefore the very earl\- writers were 

 inclined to believe the outer eye trouble followed sympathetically 

 from the retinal injury. These retinal disturbances also led Terrier ^^^ 



