556 



WERNER K. NOELL 



that it results from damage to other eye structures, such as choriodal blood 

 vessels and pigment epithelium. 



Photoexcitation by x-radiation 



As reviewed by Lipetz (this symposium), x-rays are known to produce a 

 light sensation when the patient is well adapted to darkness. In our experi- 

 ments photoexcitation by x-radiation revealed itself by ERG changes of the 

 same kind as resulting from the application of a weak steady light upon 

 which the test flashes are superimposed. 



Figure 13 shows that the b-wave during application of x-radiation is 



Fig. 13. The photoexcitatory efTect of x-rays on ERG and optic tract response in 

 the dark-adapted state. In the top row irradiation was at a rate of 300 rads per min 

 (medium dose), in the lower row 200, 100, and 20 rads per min, respectively. For 

 better demonstration of the x-ray effect the response to two flashes of light are photo- 

 graphed on the same film in some of the records. Calibration: 100 mv. Time: 10 

 msec equals one horizontal dash. 



lower in amplitude and somewhat shorter in duration than during the con- 

 trol period, the magnitude of this change being clearly related to the intensity 

 of x-radiation. The lowest x-ray intensity of 2,000 kvp radiation at which 

 this effect was still evident was about 10 rads per minute expressed in medium 

 retinal dose (Fig. 14). Throughout the x-radiation, the test flashes of light, 

 1 every 4 sec, provoked b-waves of the same reduced amplitude as those 



