Suppression of Color Contrast and Retinal Induction by Mechanical Pressure Applied to the Eyeball

Abstract

The electrical excitability of the dark-adapted eye is increased following an illumination. The effect of a white test light to increase the electrical excitability is remarkably modified when it is preceded by a condition-ing colored light. This modification is measured by the difference between the effect of the white light preceded by colored one and that of the white test light alone. When the conditioning and the test stimuli illuminate successively one and the same retinal area, the effect is called direct induction. It is called indirect induction, when adjacent areas are illumi-nated by the two lights.
1. It was shown that direct induction was little affected when the eye was repeatedly excited by strong white light in the interval between the conditioning and the test lights.
2. Direct or indirect induction was shown to be very sensitive to a mechanical pressure applied to the eyeball. A pressure of 50g. was found to be sufficient to abolish the induction when it was applied to the eye in the interval between the conditioning and the test lights. A pressure of 480g. just stopped the pulsation at the central retinal artery.
3. The depressant effect of a mechanical pressure upon retinal induction outlasted the pressure. Complete recovery occurred in 6, 7 and 10.5 seconds after removal of pressure, 50, 100 and 200g. respectively.
4. Simultaneous color contrast was produced by the method of colored shadows, and its susceptibility to mechanical pressure was investigated. In three of four subjects colored shadows were selectively abolished by a mechanical pressure applied to the eyeball when the intensity of inducing colored light was not too high.
5. The inhibitory effect of mechanical pressure was interpreted as due to anoxia caused by reduction of the rate of blood flow in the retinal capillaries, as was evidenced by entoptic observations of the retinal blood flow.