Effects of Ionizing Radiation 

 on Visual Function 



Leo E. Lipetz 



Institute for Research in Vision, 



Ohio State University, 



Columbus, Ohio 



Research workers studying the visual system have measured spectral sensi- 

 tivity (or, in the jargon of radiobiology, relative biologic effectiveness) 

 qualitatively for nearly 300 years and quantitatively for over 100 years 

 (Duke-Elder, 1938). As a result, a great deal of experience has been ob- 

 tained with problems similar to those now of interest to radiobiologists. 



The clearest single principle that has emerged from these centuries of 

 study of the effects of radiation on the visual system is the importance of 

 the organization of that system in determining the effect observed. It has 

 turned out that the organization of the biologic system is crucial at all 

 levels from the molecular through the organismic. 



Consider the finding that 7 photons (each of at least 1.8 ev energy) 

 absorbed simultaneously, one each in 7 human photoreceptor cells, can 

 cause the following sequence of events before a subject pushes a button to 

 indicate he has seen a flash of light: activation of the 7 photoreceptor cells; 

 activation of at least one bipolar cell each of the retina, ganglion cell of the 

 optic nerve, neuron of the lateral geniculate body, and neuron of the optic 

 cortex; and a change in activity of at least several hundred optic cortex 

 neurons, an vmknown number of motor cortex neurons, several hundred 

 motor fibers, and several thousand muscle fibers (Adler, 1953; Fulton, 1955; 

 Hecht et al., 1942; Polyak, 1957; Walls, 1953). 



Consider further that the action potential produced by each of the acti- 

 vated neurons and muscle fibers involves the movement out of the cell of 

 about 4 X 10^^ ions per cm- of nonmyelinated cell surface (Hodgkin, 1951). 

 So at least 10^^ ions have been caused to move as a result of the absorption 

 of only 7 photons with an energy content of about 13 ev. Since each ion 

 moves against an electric potential of about 0.1 volts (Hodgkin, 1951), this 

 is an energy change of about 10^- ev. The chance of such a small energy 

 input causing such a large energy change in a random ensemble of atoms 

 is infinitesimal. It is apparent that the biologic system must be highly organ- 



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