540 LEO E. LIPETZ 



threshold was caused by further x-irradiation up to 150 r. After x-irradiation, 

 this lowered threshold remained constant in the dark for at least 6 hours. 

 When the eye was lioht-adapted and then dark-adapted after the x-irradia- 

 tion, the lioht threshold always returned to the normal level, indicating that 

 the x-irradiation had acted on the photochemical system of the eye. The 

 visual pigment of the Limulus eye is known to be similar to that of the 

 vertebrate eye (Hubbard and Wald, 1960). 



Brinkman and Lamberts (1960) measured the over-all change in electric 

 potential appearing across the whole eye (electroretinogram or ERG). He 

 found that a detectable ERG could be produced in the intact frog's dark- 

 adapted eye by momentary exposure to as little as 1 r x-irradiation. 



Gurtovoi and Burdianskaia (1959) determined the threshold dose to the 

 dark-adapted human eye to produce a sensation of light. They found that 

 the threshold varied from person to person, but was constant for months for 

 a given person. For a 0.14 sec irradiation the thresholds of 5 subjects lay 

 somewhere between no response at 0.3 mr and lOO^r response at 3.0 mr ± 

 20%. For shorter durations, the threshold dose was somewhat reduced. Their 

 results are in good agreement with the 0.5 1.0 mr threshold found by Born- 

 schein et al. (1953) for a 0.020 sec duration. 



Lenoir f 1944) measured the course of dark-adaptation (to light) in 

 cancer patients before and after many days ot therapeutic x-irradiation. In 

 every case the rate of initial dark-adaptation was slowed, and in most cases 

 the final light threshold was raised. 



Baily and Noell (1958) measured the doses of 100, 250, and 2,000 kvp 

 x-rays needed to produce acute and irreversible reduction of the rabbit's 

 ERG response to light. The doses agreed closely with those that produced 

 death (lysis) of the visual cells. The relative biologic efficiency was greater 

 for x-rays with lower linear energy transfer. This suggests that in the visual 

 cell there are only a few^ critical sites of rather large extent which need be 

 damaged to interfere irreversibly with the metabolism, causing reduction of 

 the ERG amplitude in a few minutes and cell death in a few days. 



References 



Adler, F. H. 1953. "Physiology of the Eye, Clinical Application" 2nd ed.. Chapter 

 16. Mosby, St. Louis, Missouri. 



Avakyan, Z. M. 1958. cited in Lcbedinsky, A. V., Grigoryev, Y. G., and Demirchogl- 

 yan, G. G. 1959. The biological effect of small doses of ionizing radiation. Proc. 2nd 

 Intern. U.N. Conf. on Peaceful Uses of Atomic Energy, Geneva, 1958 22, 17-28. 



Baily, N. A., and Noell, W. K. 1958. Relative biological effectiveness of various 

 qualities of radiation as determined by the electroretinogram. Radiation Research 

 9, 459-468. 



Baylor, E. R., and Smith, F. E. 1958. Animal perception of .\-rays. Radiation Re- 

 search 8, 466-474. 



