EFFECTS OF RADIANT ENERGY ON THE EYE. 725 



case like this as we have already shown, but the danger was from pure 

 heat radiation of which 10% to 15% was due to pass through the 

 uviol glass. We produced in experiment No. 97 most destructive 

 effects from solar heat passing through this medium, and while Best's 

 experiment of ten seconds was below the danger limit it should never 

 be forgotten that the solar energy lies well toward the blue end of 

 the spectrum, and media which successfully cut out the red and infra 

 red are of very little service in protection against solar radiation. 



Thermic Effects on the Retina from short Circuits. 



It is worth noting in connection with eclipse blindness that sources 

 of intense energy other than the sun may produce similar results. 

 For example, Uhthoff ^^^ reports the case of a patient exposed to a 

 violent short circuit in which a fortnight after the accident grayish 

 spots due to alterations in the pigment epithelium were observable 

 in the macula of the left eye and were still observable six months later. 

 This ophthalmoscopic appearance is closely similar to that many 

 times recorded in eclipse blindness. Still later Knapp ^°^ records a 

 case of bilateral injury produced by a tremendously powerful short 

 circuit occurring a scant half meter from the patient's face. There 

 was complete temporary scotoma followed on the next day by some 

 superficial symptoms indicating photophthalmia, and a week later by 

 metamorphopsia, while the vision had been steadily sub-normal. 

 In each fundus was a patch corresponding to the image of the short 

 circuit flare, in which serious damage had been done. These injured 

 areas were still obvious a year later. The retinal lesions described, 

 and especially the metamorphopsia, are such as are typical in the case 

 of eclipse blindness. Here the energy radiation of the short circuit 

 was concentrated in the image to an extent sufficient to produce a 

 typical thermic lesion. The slightness of the abiotic radiation re- 

 ceived is evidenced by the very brief superficial symptoms, and the 

 retinal injury, owing to the absorption of practically the whole ultra 

 violet by the media of the eye, must have been due essentially to 

 the pure energy radiation of which the amount, judging by the de- 

 scription, was probably not less than 100 to 200 kw. A short circuit 

 involving 100 kw. would give a superficial intensity at a half meter of 

 over 30,000,000 ergs per square cm., that is, more than thirty times 

 the intensity of solar radiation. The area of the scotoma produced 



