584 RADIATION BIOLOGY 



the eye, whereas the posterior portion of the eye exhibited very sHght 

 differences. These findings are consistent with volume conductor effects 

 based on high electrical resistance at the anterior pole of the eyeball. 

 They certainly bear repeating, however, now that electronic recording 

 enables us to distinguish clearly between current and potential differences. 



There appears to be some parallelism between the resting potential of 

 the eye and the action potential in response to a flash of light. The 

 polarity of the main (5-wave) aspect of the electroretinogram is similar 

 to that of the resting potential in both vertebrate and invertebrate eyes. 

 Thus the 6-wave appears as an increase in the potential already present, 

 though we must not conclude from this that the two arise within the 

 same retinal cells. More direct evidence is found in Therman's finding 

 (1938) that glucose augments both the action and resting potential, 

 whereas potassium has opposite effects. It is notable, however, that the 

 resting-potential polarity of an excised eye has commonly been observed 

 to deteriorate and indeed become reversed, whereas the action-potential 

 polarity maintains its usual direction. Wulff (1948) has reported evi- 

 dence that both the resting and action potential of the frog are subject 

 to a rapid decline after the eye has been excised. The ratio of resting 

 potential to action potential is not constant, however, except under con- 

 ditions where the eye remains fully dark-adapted and is stimulated by 

 relatively weak flashes of light. 



Regardless of its origin, the resting potential has been the basis for a 

 convenient method of recording eye movements. Miles (1939a, b) and 

 Carmichael and Dearborn (1947) have studied in detail the changes in 

 polarity between electrodes placed on the skin at either side of the human 

 eye during reading or other activity involving deliberate rotation of the 

 eyes. Although it may be that some external effects are involved here, 

 notably responses of the large external muscles that serve to rotate the 

 eye, a major portion of the effect seems to be attributable to the fact 

 that the positive or corneal pole of the eyeball moves toward one electrode 

 And away from the other for any given rotation of the eye.^ 



THE ELECTRORETINOGRAM 



Relatively slow action potentials are developed by the retina as a 

 whole in an eye that is stimulated by light. Records of this phenomenon 

 may be obtained by placing electrodes directly across the retina or by 

 placing one on the anterior pole of the eyeball and the other at the fundus. 



2 Incidentally in our laboratory we have noted a marked diminution in potentials 

 arising from eye movements in a patient with retinitis pigmentosa. This patient, like 

 others similarly afflicted, also showed an almost complete loss of the action potential. 

 Our observation is therefore consistent with the notion of a common retinal origin 

 for both resting and action potential. 



