552 



WERNER K. NOELL 



100 



PRE 



10 12 



VA 



2 4 6 6 



HOURS 

 Fig. 10. ERG (b-wave) decline after 4,800 rads (medium retinal dose, 250 kvp) 



4 6 



DAYS 



decline between 4 and 8 hours after irradiation (Fig. 10). This transient 

 b-wave change coincided with an a-wave increase, whereas during the early 

 postirradiation period both waves diminished almost simultaneously. 



A rapid ERG decline immediately following irradiation was consistently 

 associated with visual cell death. In fact, death of the visual cells in the 

 most exposed retinal region occurred when irradiation was insufficient to 

 produce a sudden ERG decline but effected a more slowly developing ERG 

 reduction. Using 2.000 kvp radiation, visual cell death was found when the 

 absorbed dose was 4.000 rads, whereas a rapid ERG decline required an 

 average minimal dose of 4.300 rads to the most exposed retinal region. On 

 the other hand, a slight ERG reduction developing slowly within 1 to 2 hours 

 after irradiation was generally not associated with visual cell death. The 

 minimal dose required for such a slight ERG change was only 10-20% lower 

 than for visual cell death. Obviously, cell deaths and ERG effects are very 

 closely related. 



The preservation of an ERG, whatever its size, 24 hours after irradiation 

 was indicative of the survival of a fraction of the visual cells for the whole 

 postirradiation period, i.e. up to about 2 weeks. Our observations suggest 

 that visual cells which still function 24 hours after irradiation survive, 

 whereas those which do not function at this time have died. 



Effects on Metabolic Activities 



The metabolic activities of retinas isolated from eyes after x-irradiation 

 were measured in the Warburg flask (Cohen and Noell, 1960). The eyes 

 had been exposed to 2,000 kvp irradiation of varying total dose applied up 

 to 20 minutes. Their ERGs were recorded throughout irradiation and until 

 5 minutes before eye removal. The incubation medium was routinely Krebs- 



