Search PubMed⌕ Search

Biomedical subjects

D van Norren

Publications and source records attributed to D van Norren.

At least 73 records · Page 4Linked to original sources
PubMed1983

Densitometric measurement of human cone photopigment kinetics.

We measured the radiance response function for steady state bleaching lights and the regeneration of the cone visual photopigments using the continuous recording densitometer described by v. Norren and v.d. Kraats. Measurements made on 5 deuteranopes, 1 protanope and 2 color-normal observers were similar. The radiance response function was steeper than the function predicted by a simple first-order kinetic equation. For a measured density (ca 0.3) we evaluated whether high stray light (ca 47.5%) and high two-way optical density (ca 1.3) could account for the deviation from the prediction of a first-order equation. Such a model was rejected because these parameters predicted different estimates of the time course of regeneration for different test wavelengths (554 and 605 nm). Statistical analysis of the regeneration data revealed a highly significant non-linearity. A model in which the rate of regeneration increases as the proportion of bleached photopigment decreases is required to explain both the radiance function and the regeneration data.

Adult↗
PubMed1983

Light adaptation of primate cones: an analysis based on extracellular data.

Extracellular photo-cone responses were isolated in the intact rhesus monkey eye by fractional recording across the outersegment layer in the fovea with a bipolar microelectrode. The cone response vs intensity function was determined in the presence of adapting backgrounds up to 10(6) td. Increment and decrement responses, as well as the response to the steady backgrounds were recorded. All steady state and transient response data could be described with the equation V/Vm = In/(In + sigma n) with n = 0.74 and V and I representing total response and total incident light intensity. This invariant response function is shifted both along the intensity and the response axis with increasing background intensity. The decrease in sensitivity, corresponding to these shifts, could be attributed to cellular adaptation (sigma-adaptation), pigment bleaching and response compression. An analysis of the threshold vs intensity function shows how each of these mechanisms contributes to produce Weber behaviour.

Adaptation, Ocular↗
PubMed1983

Foveal densitometry in retinitis pigmentosa.

Cone density and psychophysical thresholds were investigated in patients with retinitis pigmentosa. Our aim was to assess possible disturbances of foveal cones, especially in patients with good visual acuity. Using the continuously recording densitometer described by van Norren and van der Kraats, we examined ten patients (19 eyes). With the same apparatus it was possible to determine cone final threshold. In all patients double density values were lower than in an age-matched and sex-matched control group of an equal number, and the half time of regeneration was increased in eight eyes. In 12 eyes of eight patients the foveal final threshold was raised above normal. Pseudoprotanomaly was found in seven eyes in four males. Possible explanations for these findings are discussed. Since reduced double density was found in all patients with retinitis pigmentosa, we conclude that disturbed foveal cones are probably a common and rather early feature in this disease.

Adult↗
PubMed1982

Fractional recording and component analysis of primate LERG: separation of photoreceptor and other retinal potentials.

The local electroretinogram, as obtained with a single micro electrode in the rhesus monkey fovea is known to be the sum of a number of components. This paper shows how the receptor component may be isolated from the LERG by using a bipolar micro electrode that records the potential across the outer segments of the foveal cones. A component analysis of the single electrode LERG, performed at a number of electrode depths in the retina, yields four components: a receptor-, b-, dc- and slow component. The latter has not been reported previously in the monkey and it is proposed that this is the slow PIII of the primate retina. The amplitude-depth profiles of the four components show why the receptor component may be isolated by fractional recording. The recording area of a bipolar electrode is 10 times smaller than that of a monopolar electrode. Contribution of rods to the responses is often present in the dark adapted foveal LERG but is absent in fractional records from the central fovea. The infusion of sodium aspartate in the eye abolishes the b-component, but does not affect the slow component. Aspartate produces, however, such further complexities that the method seems not suitable for isolation of the receptor potential in the intact primate eye.

Animals↗
PubMed1982

Intraretinal recordings of slow electrical responses to steady illumination in monkey: isolation of receptor responses and the origin of the light peak.

The onset of steady illumination of the mammalian retina initiates a series of complex electrical responses. Corneal recordings in man show a relatively fast ERG, followed by a much slower "light response": a "light peak" followed by a series of damped slow oscillations that may last for 1 or 2 hr. The latter oscillations are a prominent feature of the EOG. We recorded the response to steady illumination with micro electrodes in the intact rhesus monkey eye. The intraretinal "light response" was analyzed by simultaneous recordings at different depths, using a bipolar microelectrode. We found that a steady photoreceptor component can be isolated by fractional recording across the cone outer segment layer in the fovea. Further, through simultaneous recordings at the retinal and choroidal sides of the retinal pigment epithelium, we found that this structure is most probably the generating site of the "light peak" and subsequent oscillations of the standing potential.

Animals↗
PubMed1981

A case of incomplete achromatopsia of the deutan type.

A 45 year old man was studied who was previously diagnosed as a typical achromat. Increment spectral sensitivity measurements on white and several colored backgrounds showed that he possessed a rod system, a cone system sensitive in the short wavelength region (blue cones) and a cone system sensitive in the long wavelength region (red cones). This investigation shows that rather extensive testing is required to classify incomplete achromats.

Color Perception Tests↗
PubMed1980

Visual acuity measured with pupil responses to checkerboard stimuli.

The response of the pupil was measured to a foveally fixated small field in which checkerboards were alternated with a blank field of equal average luminance. The subjects studied had refractive errors, but their eyes were free from pathological changes. A pupil visual acuity could be derived, which showed a very high correlation with the subjective acuity with the same checkerboard stimuli. The method of obtaining pupil visual acuity seems to compare favorably with other objective methods of measuring visual acuity.

Adolescent↗
PubMed1978

Blue cone function in a family with an inherited tritan defect, tested with electroretinography and psychophysics.

The sensitivity of the blue cone system to low frequency flicker was tested with a psychophysical and an electroretinographical method. With the psychophysical method the subjects, members of a family with an inherited tritan defect, showed no sign of the presence of the blue cone system. With the electroretinogram the sensitivity was also significantly lower than in normal subjects, thus indicating a retinal origin of the tritan defect.

Adolescent↗