[A battery model of the eyeball to calculate standing potential of the eye].

Variation of the resting potential caused by eye movements was analyzed by applying a battery model to the eyeball. A formula that gives the potential between the inner canthus and the outer canthus of the eye was derived on the basis of the electric theory in electromagnetics, on the assumption that the eyeball was floating in a homogeneous conductor. The variations of the resting potentials were represented using the distance from the center of the eyeball to the potential detecting position and the deflection angle of the position with respect to the optical axis of the eyeball. To verify the validity of the formula, the variation of the resting potential caused by the various amplitudes of bilaterally symmetrical eye movements were measured. The calculated results were found to be in good agreement with the experimental ones.

[Reducing cross-talk in electrooculograms made with several electrodes].

In order to discuss how to handle the contralateral effect (cross-talk) when taking an electrooculogram (EOG) with two or more electrodes, a forced duction test was used to detect cross-talk potentials. The cross-talk potentials originating from the left eye were measured at the right eye for 5 subjects when the left eye was adducted and abducted alternately with a suction contact lens while the right eye was kept fixed. The cross-talk potentials detected at the right eye did not depend on the electrode position, but the contralateral EOG potentials depended on the electrode position around the left eye. The cross-talk value is calculated as the gain, 20.log [(cross-talk potential)/(contralateral EOG potential)]. The denominator of this expression considerably affects the gain since the contralateral potential depends on the position of the electrode. We propose that the effect of the cross-talk on the potential between a pair of electrodes can be cancelled with the gain value (-15.0dB: the mean value for the 5 subjects) when the contralateral electrode is set 20 mm from the outer canthus.

[Characteristics of the EOG potential changes generated by saccadic eye movements of large amplitude].

The time curve of the electrooculogram (EOG) as applied to clinical diagnosis is measured as the changes in the standing potentials around the eyes when a subject performs saccadic eye movements of constant amplitude. If the characteristics of these potential changes caused by the eye movements are known, the time curves of EOG can be derived from the potential changes generated by saccadic eye movements of random amplitude, by transforming the measured potentials into the exact values corresponding to the constant amplitudes of saccades. We have already reported that the characteristic curves of EOG are proportional to the angles of the eye movements within +/- 20. However, Fenn and Hursh reported that the characteristics of saccadic eye movements for larger amplitudes up to about 80 degrees were sinusoidal functions. Other workers have reported linear relations of the characteristics of EOG. In this report we attempted to clarify whether the characteristics of EOG were linear or sinusoidal. From our experiments it became clear that the characteristics of EOG could be approximated to straight lines up to about 80 degrees (visual angle).

[The relation between saccadic eye movements and electrooculogram during light and dark adaptations].

The relation between the amplitudes of saccadic eye movements and the resting potential changes detected around human eyeballs under light and dark adaptations was clarified by means of simultaneous measurements of electrooculogram (EOG) and eye movements. The authors previously reported that the potential changes are proportional to the horizontal saccadic eye movements within +/- 15 degrees (visual angle) under conditions of the room light of approximately 60 lux. There are few reliable data indicative of the presence of the above relations under light and dark adaptations. The result of the simultaneous measurements of EOG and eye movements during the light and dark adaptation at 2-minute intervals in 9 normal subjects showed that the resting potential changes were in direct proportion of the amplitudes of the saccadic eye movements at any time within +/- 20 degrees. In these experiments, the eye positions were monitored with the eye mark recorder during the eye movements. In case the eye positions excursioned from a target, the exact EOG was calculated by measuring eye positions and correcting the EOG errors.

[Correction of EOG with eye movement measured by the eye mark recorder system].

The electrooculogram (EOG) is usually necessary for the subject to fixate two targets alternately at a fixed visual angle. However, in the patients with poor vision, it can be difficult to fixate exactly. In such case, the results can be improved by using both the measurement of real eye position and the measurement of EOGs in combination. In this study, we measured subject's eye position simultaneously with the potential changes around his eyes as the subject pursued alternately two on-and-off visual targets which were horizontally placed on the cylindrical screen at a regular visual angle in front of his eyes. The EOG is obtained from those potential changes. If the difference between the target position and the fixating point can be calculated from the net eye movement measured with an eye camera, the error potential can be derived from this difference. Therefore, exact potential changes are obtained by correcting the measured potentials with the above error potentials. The authors were able to confirm that the potential changes were approximately proportional to the amplitude of saccadic eye movements within about 30 degrees in front of the eyes. Therefore, the simultaneous measurement of the potential changes and the eye position enable measurement of EOG without pursuing the targets by transforming the measured potentials into the exact values corresponding to the constant amplitudes of saccades.