Browsing by Author "Schultz, David Noel"
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Item Standardization of the electro-oculogram of normal human subjects using Fourier analysis(1974) Schultz, David Noel; Pitts, Donald G.; Rawlings, Samuel C.; Aucoin, Anthony A.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.Item The asymmetric character of central and peripheral corneal astigmatism as determined by photokeratoscopic measurements(1977) Schultz, David Noel; El Hage, Sami G.; Pitts, Donald G.; Paton, David M.; Hayre, Harbhajan S.; Troelstra, ArneA new photokeratoscopic system of analysis which involved the computation of the radii of curvature of the anterior surface of the cornea was used to achieve an improved description of corneal astigmatism. It was hypothesized that the photokeratoscopic measurements would reveal the existence of two axis semi-meridians and two power semi-meridians which did not have an angular separation of 90[degrees]. It was also hypothesized that an evaluation of the peripheral corneal astigmatism would demonstrate that its magnitude was different than the amount of central corneal astigmatism. Measurements of photokeratographs of 30 corneas, selected for central keratometric astigmatism greater than 0.750 D., showed that there actually were four principal semi-meridians with angular separations other than 90[degrees] instead of two principal meridians 90[degrees] apart. The angular extents of each of the four corneal sectors formed by adjacent principal semi-meridians ranged from 55.0[degrees] to 122.5[degrees] for the 30 corneas. The astigmatism varied among the four sectors of each cornea, and it changed from center to periphery within each sector. The astigmatism was greater in the superior corneal sectors than in the inferior, and it was larger nasally than temporally. The general trend peripherally was an increase in astigmatism in the two nasal corneal sectors and a decrease in astigmatism in both temporal sectors. The variations in astigmatism were due to differential rates of corneal flattening. The slope of the central 2.000 mm of each principal semi-meridian was 0.00 which indicated the presence of an optic zone. The slopes of the principal semi-meridians progressively increased peripherally but at different rates. Theoretical and clinical implications of the asymmetric nature of corneal astigmatism were discussed.