EFFECTS OF RADIANT ENERGY ON THE EYE. 711 



apparatus. Second, there are many recorded instances of traumatic 

 erythropsia some of which at least evidently are associated with 

 the actual infiltration of the eye media with blood. Third, one finds 

 a vast majority of instances which one may term photo-erythropsia 

 in which the observed appearances, one can hardly dignify them by 

 the name of symptoms, are associated with over exposure to light. 

 These are so entirely without pathological significance that we should 

 hardly consider them here save for the fact that the phenomena have 

 been by some writers like Widmark *^^, Fuchs ^^^, and others, subse- 

 quently attributed to the effect of ultra violet radiations. As this 

 erroneous conception of the fact still persists in spite of the admirable 

 work of Vogt,^°^ it is desirable here to note the relation of this so-called 

 erythropsia to the general phenomenon of color vision. The whole 

 subject was thoroughly investigated recently by Wydler ^^^ who very 

 plainly showed that erythropsia is due to the red phase of the negative 

 after image following over-exposure to light, ordinarily brilliant white 

 light, although green and blue green illumination is even more effective. 

 The association of the phenomenon with ultra violet radiation appears 

 to be due to the fact that photo-erythropsia has been often observed 

 after the intense glare which produces snow blindness and not infre- 

 quently in the aphakic eye after an operation for cataract. That the 

 ultra violet really has nothing to do with the matter is clearly shown 

 by Vogt ^°^ who found that erythropsia could not be produced experi- 

 mentally by the ultra violet rays alone, but very easily by light rays 

 containing no ultra violet. We need only add here that it is possible 

 to produce marked erythropsia through euphos glass which transmits 

 no ultra violet, through B-naphthol-disulphonic acid which also cuts 

 off the ultra violet, and through dense flint glasses which eliminate 

 all of the ultra \aolet which could with any certainty get through the 

 lens. Also it is produced with great facility by radiation through 

 green and blue green media which intercept the ultra violet com- 

 pletely, but flood the eye with light of a color certain to produce a 

 strong red phase in the after image. The truth seems to be that the 

 so-called photoerythropsia is merely the result of such unequal fatigue 

 of the primary color sensations as leaves for a greater or less time there- 

 after a color sensation predominantly red. This conception clears 

 up at once the difficulty of accounting for the partial erythropsia 

 which has been noted by Purtscher ^^^ and others, since in cases of 

 unequal exposure of various parts of the retina to brilliant light the 

 fatigue effects necessarily must vary over the field of vision. A glance 

 at figure (6) will render the situation clear. The curves in this figure 



