PubMed Health⌕ Search

Biomedical subjects

E Dodt

Publications and source records attributed to E Dodt.

12 recordsLinked to original sources
PubMed1992

Scotopic versus photopic pattern onset-offset electroretinograms.

We investigated the contribution of rods and cones to the human pattern electroretinogram to onset and offset checkerboards of different spatial frequency and wavelength in a 39 degrees x 39 degrees field. Under strictly scotopic conditions, there was a negative potential at onset and a positive potential at offset, whereas under photopic conditions, there was a positive potential at onset and a negative/positive potential at offset. Thus, the waveform to pattern onset (offset) was that of the luminance electroretinogram to decreasing (increasing) luminances. For pattern onset, the sensitivity difference 486-601 nm under scotopic and photopic conditions closely followed the luminosity function of rods and cones. The amplitude of the scotopic onset response increased with check size up to 3 degrees 30' and that of the photopic onset response, up to 30'. With larger checks, the scotopic and photopic onset response markedly decreased. This indicates antagonistic center-surround organization of the receptive fields under both scotopic and photopic conditions. By contrast, the offset response monotonically increased with check size under scotopic and photopic conditions, which suggests a luminance component in the pattern electroretinogram. Consequently, the pattern electroretinogram to reversing checkerboards has to be regarded as a mixture of both pattern- (contrast) and luminance-specific components.

Adolescent↗
PubMed1991

Spatial frequency of the human short-wavelength-sensitive (blue) cone mechanism. Psychophysical studies and pattern-reversal visual evoked potentials.

The interactions of spatial and chromatic processing of the short-wavelength-sensitive cone mechanism were studied in humans with patterned (checkerboard) stimuli of various spatial frequency (10, 22, 44, and 85 min of are respectively), under steady exposure to yellow light (575 nm, 390 cd/m2). Psychophysical studies and pattern-reversal visual evoked potentials were employed. Parameters of the transient pattern-reversal visual evoked potentials (pattern reversal rate of 2.4 s-1) especially observed were the latencies of P2 (P100) and N3 and the amplitude of P2-N3. It was only with the largest applicable check size (85 min of arc) that both the psychophysical studies and visual evoked potentials could succeed in satisfactorily isolating the short-wavelength-sensitive cone mechanism. Pattern-reversal visual evoked potential latencies are recommended in the evaluation of this cone mechanism because of their smaller variance and higher selectivity in isolating the short-wavelength-sensitive cone mechanism than the amplitude. The peak sensitivity of this cone mechanism was shown to be about 449 nm at the corneal level. The short-wavelength sensitive cone mechanism represented the characteristics of low spatial resolution and long latencies of the pattern-reversal visual evoked potentials.

Adult↗
PubMed1991

[VECP (pattern threshold, amplitude, latency) in different light levels. A comparison between healthy eyes, organic and functional amblyopia eyes].

According to Bjerrum [5] and Ammann [2], light attenuation decreases visual acuity at different rates in normals, organic and functional amblyopes. In 27 normal subjects, 19 patients with central fixating squint amblyopia and 12 with organically poor vision, we determined the visually evoked cortical potential (VECP) threshold check size, P100 latency and P2 amplitude for reversing checkerboards of variable size at different levels of luminance. After light attenuation, we found a different rate of change for VECP threshold check size in normal subjects and patients with squint amblyopia, which lessened after the fovea was occluded. With suprathreshold checks, normal subjects and patients with squint amblyopia exhibited significantly smaller amplitude/latency changes after light attenuation than patients with organically poor vision. Only patients with squint amblyopia exhibiting a visual acuity of greater than 0.2 showed smaller VECP changes than normal subjects during light attenuation. According to these findings, the different rate of change in visual acuity after light attenuation in normal subjects and patients with squint amblyopia is locus specific [7] rather than luminance specific [12, 13]. We conclude that cortical disinhibition of the parafoveal retina [20] is responsible for the preservation of visual acuity in squint amblyopia during light attenuation.

Adolescent↗
PubMed1990

Cone interaction and color substitution as revealed by pattern ERG.

Transient electroretinograms to a reversing color-contrast checkerboard pattern (P-ERG) were recorded in a protanomalous, a deuteranomalous, and a normal observer. Alternate monochromatic checks were of constant wavelength (630 nm red-531 nm green), while the relative energies were varied systematically. When changing the radiance ratio 630 nm-531 nm of the stimulus, the normal subject exhibited a P-ERG to all stimuli with only a relative amplitude minimum at a distinct radiance ratio, whereas the color-deficient observers failed to show a P-ERG at some color contrast 630 nm-531 nm, the radiance ratio of which was different in the protan and deutan. From the radiance ratio of color contrast for the smallest potential in the normal observer, we conclude that the green- and red-sensitive cone mechanism provides a difference signal which generates the response. The data from the color-deficient observer support the view that color discrimination in protans and deutans is reduced because the input of one type of photoreceptor is missing.

Adolescent↗
PubMed1990

Spatial selectivity of pattern electroretinogram components.

Pattern electroretinograms were recorded to checkerboard stimuli of various check size to both onset-offset pattern and pattern reversal under most similar conditions of contrast and luminance. With onset-offset pattern the amplitude of the p-q and q-r components of the onset response showed a peak for checks of about 20 min of arc (spatial tuning), whereas the offset response was spatially nonselective at high contrast regardless of the luminance level. With pattern reversal the potentials were similar to those after algebraic summation of onset and offset responses both in waveform and check size of peak amplitude at 50 min of arc. From this we conclude that summation of contrast (onset) and luminance (offset) components is responsible for the shift from 20 min of arc (onset tuning) to 50 min of arc (reversal tuning). The study recommends the application of pattern stimuli in an onset-offset mode for studying antagonistic receptive field properties in the human electroretinogram.

Adult↗
PubMed1990

Visually evoked potentials in response to rotating plane-polarized blue light.

Visually evoked cortical potentials closely related to the appearance and disappearance of Haidinger's brushes were obtained in response to onset and offset of rotation of plane-polarized blue light. The method provides a means of investigating macular function in man; it is fairly independent of ocular opacities and relates, for the first time, entoptic phenomena to those evoked by extrinsic light stimulation.

Adult↗
PubMed1989

Pattern electroretinogram peak times as a clinical means of discriminating retinal from optic nerve disease.

Fifty-two patients with unilateral or bilateral retinal or optic nerve disease exhibited abnormal peak times and/or amplitudes in the pattern electroretinogram. While this abnormality in patients with optic nerve diseases was confined to an amplitude reduction, 40% of the eyes with retinal diseases exhibited additionally a peak time delay of the p and/or q component. We conclude that recording of pattern electroretinogram peak times provides an additional means to distinguish retinal from optic nerve diseases.

Adolescent↗
PubMed1989

Pattern electroretinogram of the blue cones.

In man the electroretinogram to pattern reversal stimuli (P-ERG) represents a cone response of the proximal retina, dominated by the cone mechanisms sensitive to red (R) and green (G). Additionally there is a cone mechanism sensitive to blue (B) which can be studied with and without steady exposure to yellow light. During exposure to a superimposed uniform yellow background (576 nm) the transient P-ERG of the B cones is represented by potentials of small amplitude (less than 1 microV). The latency (peak time) of the response is about 30 ms longer than that of the midspectral (R and G) cones. Furthermore, the P-ERG of the B cones saturates at low luminances and exhibits a maximum amplitude at about 460 nm. Without yellow adaptation, the P-ERG of the B cones can be studied only with low-intensity stimuli of short wavelengths. Near threshold, both the long-latency response of the B cones and the short-latency response of the R and G cones are recorded simultaneously, forming a double-peaked wave shape. At suprathreshold luminances, even of short wavelength (435 nm) the P-ERG of the B cones is concealed by the larger short latency response of the midspectral cone mechanism.

Adolescent↗
PubMed1989

[Postoperative recovery of visual function in sella tumors: prognostic assessment by electro-ophthalmologic studies].

Preoperative examination of the visual system in patients with tumors of the sellar region is usually limited to checking the visual acuity, assessing the visual field, and ophthalmoscopy of the optic disc. In addition to these tests we investigated pre- and postoperatively 35 patients with meningiomas, pituitary adenomas and other sellar and parasellar tumors by recording the pattern electroretinogram (PERG) and the pattern-evoked cortical potential (PVECP) in order to evaluate functional and possible structural impairment of the visual pathway. Based on electro-ophthalmological tests, the retinal and cortical findings were classified as: regular ERG and VECP (0), regular ERG and irregular VECP (1), irregular ERG and VECP (2). Up to six months postoperatively, eyes with alteration of the VECP alone (category 1) showed recovery of visual function, while those with alteration of ERG as well (category 2) did not recover in visual function. Since loss of the PERG or long-lasting alteration of it is indicative of irreversible impairment of the inner retinal layers including the retinal ganglion cells, repeat examination of the pattern ERG is recommended in disturbances caused by alterations in the central nervous system.

Adenoma↗
PubMed1975

Early receptor potential from the pineal photoreceptor.

Rapid photoresponses were obtained from the pineal organ of Rana catesbeiana and Rana esculenta comparable to the early receptor potential (ERP) of the retina of their lateral eyes. Light source was a xenon filled discharge tube with a maximum energy input of 365 J. The flash duration was 600 mu sec measured at 1/3 peak amplitude. The response pattern of the ERP of the exposed Epiphysis cerbri (intracranial portion of the frog's pineal organ) resembled the ERP of the isolated retina and the R1 deflection of the ERP of the eye-cup. It was greatly diminished during consecutive flashes and was absent during light adaptation. It was confined to the Epiphysis cerbri and was similar in time course and shap to, though smaller as, the ERP of the isolated retina. The photoresistant component of the ERP in the eye-cup was lacking in the Epiphysis cerbri and in the isolated retina. The action spectrum of the ERP of the Epiphysis cerbri closely resembled the photopigment absorption of rhodopsin indicating that the structural cones of the pineal organ contain a photopigment different from the retinal cones of the frog's lateral eye.

Action Potentials↗