Standardization of the electro-oculogram of normal human subjects using Fourier analysis



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The electro-oculogram (EOG) was recorded on 30 normal human subjects controlled for age, refractive error, and blood pressure. The EOG data was analyzed by the currently accepted clinical method, which is the ratio of the amplitude of the first light peak to the amplitude of the first dark trough, and by the newly proposed technique involving Fourier analysis of the EOG waveform. It was hypothesized that the expression of the EOG waveform in terms of Fourier series would yield a new parameter with less variability than the EOG ratio. The parameter is the phase angle obtained as an average of the difference between phase angles of corresponding harmonics in Fourier series representing the light-adapted and dark-adapted portions of the waveform. The phase angle was hypothesized to have less variability than the EOG ratio due to its association with the entire EOG waveform. Although the phase angle is computed utilizing all the data points describing the waveform, it maintains dependency upon the dark-adapted and light-adapted components of the waveform separately in accord with the EOG ratio. In order to determine whether the phase angle would vary from the normal range in abnormal retinal conditions, the EOG was recorded on two patients with ocular pathology. It was predicted that the diminished electrical response associated with the change in electrical impedance of the retinal tissues would result in a phase shift approaching 180 degrees with progressively more severe disorders. It was found that the phase angle was less variable than the EOG ratio and that this difference could be demonstrated beyond the 99.9999 % confidence level. The phase angle was found to vary from its normal range according to theoretical predictions in the two pathological conditions of the eye studied and there was indication that the phase angle was more sensitive to ocular pathology than the EOG ratio. The results of this study indicate that the phase angle is the parameter of choice in the EOG evaluation.