ACCOMMODATION OF THE HUMAN RETINA TO EXPONENTIALLY INCREASING CURRENTS

Abstract

Using, as an index of excitation, the electrical phosphene elicited by the electric current running through the eyeball, we made a systematic study of accommodation of the retina to the exponentially increasing current, whose time-constant extended up to several hundred msec. The relation between the electric threshold (final voltage Vf) and the time-constant (RC) , namely, the so-called accommodation curve, was determined at six different levels of adaptation. The results obtained are as follows:
1) The accommodation curve for the dark-adapted eye is of duplex nature, namely, it is divided into two sections by a clear break at a time-constant of about 70-90 msec.
2) It is noticed that two sorts of subjective sensation of the electrical phos-phene are perceived in accordance with two sections of the accommodation curve.
3) The accommodation curve changes its form depending upon the intensity of illumination, where both sections of the accommodation curve shift separately upwards and sidewards respectively.
4) It is found that there are two types of the electric threshold strength-log-illumination curve. The one appears in cases of RC being shorter than 30 msec., while the other appears in cases of RC being longer than about 75 msec.
5) All these results stated from (1) to (4) may be explained by assuming two different seats of electrical excitation.
6) Hill's λ was calculated from each of both sections of the accommodation curve; the value of λ ranged between 366 and 18 msec. according to the experi-mental condition of illumination.
7) It is discussed that, if the time-constant of the exponentially increasing current is equal to a half period of the sinusoidal alternating current, both kinds of these stimuli have almost identical effects with regard to electrical excitation of the eye.