Search PubMed⌕ Search

Biomedical subjects

D Reits

Publications and source records attributed to D Reits.

10 recordsLinked to original sources
PubMed1992

Analysis of striate activity underlying the pattern onset EP of children.

The checkerboard onset Evoked Potential (EP) does not obtain its adult form before puberty. To determine the site of origin of these processes we studied the origin of the checkerboard onset EP in a group of 10 children between the ages of 6 and 16 years. Since the development of the waveform of the pattern onset EP varies with check size we also studied the dependence of these EPs on check size. The child checkerboard onset EPs described in this paper are dominated by a single source. Following an equivalent dipole source localization approach, the position, orientation and variation in strength of the equivalent dipole is estimated. The position and orientation of this dipole indicates an origin in the primary visual cortex (area 17). The variation in strength of the dipole changes from a single positive deflection, specific for children of 8 years and younger, into a negative-positive complex for the children studied between the age of 9 and 16 years. These changes in waveform must be due to changes in the activity pattern of the striate cortex.

Adolescent↗
PubMed1992

Flicker electroretinograms: a systems analytic approach.

We observed multiple maxima and minima in the electroretinogram (ERG) first harmonics which varied as a function of adaptation level, mean illuminance, and modulation depth. Based on differences in response characteristics we identified a minimum of 3 parallel mechanisms operating at 3 frequency regions within the ERG: a low frequency region (less than 10 Hz), a midfrequency region (centered near 20 Hz), and a high frequency region (centered near 40 Hz). The low frequency region was observed both in dark- and light-adapted conditions, was basically linear, and showed nonlinear behavior only at high contrasts in either light or dark adaptation. It may be modeled as a low pass filter. The midfrequency region was clearly observed only above cone threshold, was nonlinear at low contrasts, and may be modeled as a linear filter followed by an essential nonlinearity. The high frequency region was observed under high levels of light adaptation and also was nonlinear at low contrast. It may be modeled also as a linear filter followed by an essential nonlinearity.

Dark Adaptation↗
PubMed1989

Global stereopsis in human albinos.

The presence of global stereopsis was examined in 18 clinically diagnosed albinos; four non-albino controls were also tested including two observers with congenital nystagmus. Stereopsis was evaluated with standard clinical stereo tests and with TV generated random dot stereograms. The latter test involved electrophysiological measures of vertical eye movement tracking in response to a stimulus target. For either test procedure, global stereopsis could be demonstrated in a significant number of albinos across varying phenotypes. These results are of interest in view of electrophysiological investigations in albino animal models which indicate a paucity of binocularly driven cortical neurons in visual areas 17, 18 and 19. While stereopsis may be mediated in our albinos via residual appropriately projecting retino-geniculo-cortical fibres, we suggest that inter and intra cortical communication via corpus callosal connections may play a primary role in providing the adequate neural substrate for albino binocularity.

Adolescent↗
PubMed1986

Minimum procedures for visual electrodiagnostic testing.

A set of procedures for the electroretinogram, electrooculogram, and pattern and luminance visual evoked cortical potentials was defined by representatives from all Dutch University Eye Clinics in order to promote standardization of procedures for routine diagnostic testing. The procedures have been selected to obtain an answer to most electrodiagnostic questions of frequent occurrence with a minimum of equipment and examination time. An individual examiner may add other procedures to the proposed program to extend and diagnostic possibilities.

Electrodiagnosis↗
PubMed1981

Evoked potentials in albinos: efficacy of pattern stimuli in detecting misrouted optic fibers.

Misrouting of retinogeniculostriate projections associated with retinal hypopigmentation has been found to be a general phenomenon in mammals, including humans. Anomalous optic pathway projections of albinos may be detected by recording visually evoked potentials (VEPs). To determine the efficacy of various stimulus conditions for detecting misrouted optic fibers, we compared flash, modulated light, pattern reversal and pattern onset/offset (appearance/disappearance) stimuli. Pattern onset/offset were found superior in detecting anomalies of misrouting of retinogeniculostriate projections. As a group, humans with retinal hypopigmentation have poor evoked potentials to offset and pattern reversal stimuli. Nystagmus seems to be most symptomatic of poor pattern reversal responses. In general onset/offset pattern stimuli are more versatile for detection of abnormalities in the visual system than pattern reversal stimuli.

Adolescent↗
PubMed1979

Computer analysis of the EEG as an aid in the evaluation of dietetic treatment in phenylketonuria.

The effect on the EEG of the reintroduction of phenylalanine in the diet of 6 patients with PKU on treatment was studied. Patients received daily loads of 100 or 150 mg L-phenylalanine/kg, equally divided over the meals, and computerized spectral EEG analysis was performed. The following EEG changes were seen: (1) occurrence of activity in the low frequency band (2--5 c/sec), (2) change of frequency of dominant rhythms; (3) change in the degree of synchrony between identical frequencies, occurring in different derivations. EEG changes increased quantitatively parallel to increasing blood phenylalanine and reversed after stopping the phenylalanine administration, suggesting that the EEG abnormalities are a measure for the degree of intoxication caused by phenylalanine or its metabolites. It is suggested that the EEG data may be useful deciding to terminate the diet in PKU.

Adolescent↗
PubMedDate not supplied

Analysis of human tear protein profiles using high performance liquid chromatography (HPLC).

Using high performance liquid chromatography (HPLC) the tear protein profiles were measured in controls, patients with Sjögren's disease, questionable dry eye (idiopathic dry eye), idiopathic chronic conjunctivitis and the corneal melting syndrome. Qualitative comparison of the protein profiles of patients with Sjögren's disease, corneal melting and IgA deficiency shows a marked difference in the heights of various peaks as compared to the profiles of the control group. The total protein content of tears in controls and in patients with idiopathic chronic conjunctivitis is age dependent and appears to increase until the age of 40 and to decrease afterwards. The peaks containing IgA, lactoferrin and lysozyme were measured in various eye diseases. In idiopathic chronic conjunctivitis and in the corneal melting syndrome no differences were seen in comparison with controls. In patients with idiopathic dry eye and Sjögren's disease a marked decrease in the three proteins was seen. The study presented here indicates that the HPLC analysis of tears is a promising technique which may increase our knowledge of this ocular fluid.

Adolescent↗
PubMedDate not supplied

[Computer analysis of the EEG as an aid in terminating diet therapy in phenylketonuria].

In 6 patients with PKU, being on a low phenylalanine diet, the effect of reintroduction of phenylalanine on the E.E.G. was studied. The children, therefore, received daily loads of 100 or 150 mg phenylalanine/Kg bodyweight, equally divided over the meals. Computerized spectral analysis of the E.E.G's was performed during and after the loading tests. This made quantification possible of the following E.E.G. changes: 1) the increase of activities in the theta frequency band (4-8 Hz); 2) the frequency change of the alpha rhythm; 3) the change of the degree of synchrony between identical frequencies occurring in different derivations. A linear relation was found between these quantified E.E.G. parameters and the phenylalanine blood-level. After stopping the loading test E.E.G. abnormalities reversed suggesting that they could be considered as a measure for the degree of intoxication caused by the phenylalanine and/or its metabolites. It is suggested that the E.E.G. data may be useful parameters for alleviation or termination of the diet.

Alpha Rhythm↗