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Biomedical subjects

G van Lith

Publications and source records attributed to G van Lith.

9 recordsLinked to original sources
PubMed1989

Oscillatory potentials in early diabetic retinopathy.

To study the oscillatory potentials in early diabetic retinopathy the authors developed a new power measurement based on the fast Fourier transform. Three groups totalling 46 patients were examined, varying from nonvisible to preproliferative diabetic retinopathy. The oscillatory potentials expressed in microwatts were measured under scotopic and photopic conditions. The data of the three groups are compared with those of a group of 22 normal individuals. The oscillatory potential power measurement appears to be a reliable method in detecting diabetic retinopathy at an early stage.

Adult↗
PubMed1988

Measuring oscillatory potentials: Fourier analysis.

Studying the oscillatory potentials in diabetic retinopathy, the authors experienced several problems interpreting results of digital filtering. The main problem was the separation of the first potential from the a-wave, since their frequencies are within the same range. To improve the procedure of measuring implicit times and of calculating amplitudes, the filtering was started with a finite impulse response filter and followed by a fast Fourier transform. The power of the oscillatory potential was calculated by determining the dominant frequency in the Fourier transformed response and expressed in microwatts. A group of normal subjects was compared with a group of early diabetic retinopathy patients. It appears that even in pathological circumstances a quantitative expression of the oscillatory potential is possible.

Adult↗
PubMed1982

On and off contribution to the combined occipital on-off response to a pattern stimulus.

The hypothesis, derived from previous studies, that the off response forms the main part of the second positive wave (P2) in the occipital response to the presentation of patterns was tested by using stimuli of various durations. It was found that the off response merges with P2 of the on response in the combined on-off response. The question, however, whether the on response or the off response contributes most to the combined on-off response could not be answered. By applying hemifield stimulation, the experiments furthermore confirm the concept of the presence of a double dipole in the hemisphere contralateral to the stimulated side.

Evoked Potentials, Visual↗
PubMed1981

Quantitative evaluation of the electroretinogram.

The assessment of an electroretinogram (ERG) as normal, abnormal or absent is too imprecise an estimation to inform ophthalmic surgeons about the prospective visual functions. For example, an abnormal or subnormal ERG includes an almost normal as well as an almost absent ERG. Furthermore, whether an ERG is labelled as absent depends on the amplitude of the electrical background activity. A much better information can be provided by expressing the ERG in percentages of the normal value.

Cataract↗
PubMed1980

The electrooculogram and its interindividual and intraindividual variability.

The EOG was determined in 130 normal subjects. The mean value was 2.42, the interindividual standard deviation 0.42. The difference between the right eye and the left eye was not significant, neither was the difference between a group of youngsters (20-30 years) and an older age group (50-55 years). In another group of 48 normal subjects, 10 or more EOGs were determined per individual. The intraindividual standard deviation was not a fixed number, but appeared to be dependent on the height of the EOG, being approximately 10% of the EOG value. This is a confirmation of one of our previous observations.

Adult↗
PubMedDate not supplied

Measuring oscillatory potential during the course of an arterial occlusion: a method based on Fourier analysis.

Recently we developed a quantitative method of measuring the Oscillatory Potentials (OP's) for a clinical study in diabetic patients. Several problems were experienced in interpreting the results obtained with digital filtering. The main dilemma was the separation of the first OP from the a-wave, since their frequencies are within the same range. The fast Fourier transform (FFT) was applied for this purpose. From the FFT response the power of the OP's was calculated and expressed in microwatts. The advantage of this method is clearly demonstrated in the case of a patient with central retinal arterial occlusion.

Adult↗