EFFECTS OF RADIANT ENERGY ON THE EYE. 785 



iron arc and obtained well marked changes, notably chroraatolysis 

 and vacuolization of the ganglion cells, in lens containing eyes as well 

 as in two aphakic eyes. These experiments are described and dis- 

 cussed in detail on page 687. 



From the foregoing experiments Birch-Hirschfeld concluded that 

 the lens did not afford complete protection to the retina from the 

 specific action of ultra violet light. Best ^^, however, took the view 

 that no danger to the retina was to be feared from ultra violet light 

 since he found he was able to look at the sun directly without deleteri- 

 ous effects for ten seconds through a blue uviol glass wdiich transmits 

 freely the ultra violet waves from the sun, but absorbs all visible 

 waves longer than about 470 nn in length. 



Birch-Hirschfeld^^ in 1908 reported five cases of visual disturbance 

 among workers in mercury \'apor illimiination. He concluded that 

 after long occupation with unprotected eyes in mercury vapor arc- 

 light a disturbance of retinal function may result with or without an 

 electric ophthalmia or a similar conjunctival reaction. These in- 

 juries took the form of pericentral scotomata for red and green. By 

 the aid of a Priestly Smith scotometer these scotomata were mapped 

 out. The affected region had a sector or ring-formed shape at a 

 distance of 15 degrees to 20 degrees from the fixation point. Red 

 usually appeared yellowish and green as a gray or even white. The 

 central color vision was only in two cases injured in the sense of red- 

 green blindness, though floating spots often temporarily obscured the 

 fixation point. The color scotomata disappeared in the course of a 

 few weeks if protecting glasses were worn or if work in ultra violet 

 light was abandoned. 



The solar eclipse seen in Europe on the 17th of April, 1912, afforded 

 excellent opportunities for observation of ophthalmoscopic and func- 

 tional retinal changes due to sun blinding. In the series of 50 reported 

 by Birch-Hirschfeld*^, four cases showed normal eye grounds, 19 

 others had increased f oveal reflex, with frequently a concentric irregu- 

 lar reddish-brown area, which in eleven cases cleared up at the end of 

 a week. In 16 other cases there was noted irregular pigmentation of 

 the macula and small gray puntiform spots or globules which remained 

 unaltered for months. In 31 cases an absolute central and in 19 cases 

 an absolute paracentral scotoma was found which afterwards became 

 relative scotomas. The rest had relative central scotomas to begin 

 with. These were mostly eccentric downward extending 1° to lO'* 

 The majority of cases with the milder injuries regained almost normal 

 visual acuity in the course of a few weeks. In small numbers of single 



