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Biomedical subjects

E Dodt

Publications and source records attributed to E Dodt.

At least 19 recordsLinked to original sources
PubMed1996

[Effect of cataracts on contrast pattern reversal stimuli exemplified by the pattern electroretinogram].

A cataract changes pattern-evoked contrast responses to a mostly unknown extent by a blurred retinal image. Pattern electroretinograms (P-ERG), evoked by a reversing checkerboard pattern, were measured (a) in 12 healthy volunteers with a cataract simulated by Bangerter foils; (b) pre- and postoperatively in 44 cataract eyes without retinal damage; and (c) in 13 healthy contralateral eyes. Slight media opacities (visual acuity 1.0 to 0.8) already diminished the amplitudes of the pattern ERG significantly, whereas the latencies did not react significantly. This can be explained by a decrease more in contrast than in luminance. Postoperatively, the amplitudes continued to increase during the first 10 weeks, when the visual acuity remained stable. The postoperative amplitudes did not reach the amplitudes of comparable healthy contralateral eyes. It is recommended that eyes be checked for cataracts before an interpretation is made.

Adolescent↗
PubMed1995

Simultaneously recorded retinal and cerebral potentials to windmill stimulation.

Visual evoked retinal and cerebral potentials were recorded to onset rotation of an isoluminant sectored disc. While the retinal potentials recorded to onset rotation closely resembled the electroretinogram to a checkerboard or stripe pattern of fixed element size, the visual evoked potential changed interindividually and intraindividually from a fast positive wave at high contrasts, velocities and number of windmill segments to a later negative component at low contrasts, velocities and windmill segments. With change in luminance, contrast, speed and extent of rotation field size and number of disc segments, the visual evoked potential was generally less affected than the electroretinogram.

Adolescent↗
PubMed1994

[Sensory and electrical responses in stimulation of the macula with short-wave (407-527 nm) linear polarized light (Haidinger polarization brushes)].

We investigated Haidinger's (1844) entoptic polarization brushes of the macula psychophysically and electrophysiologically during rotation of plane-polarized blue (< 520 nm) light projected to a polarization screen. Psychophysically the sensitivity of the brushes was highest between 470 and 490 nm, with a steep decrease at longer wavelengths. Increase of adaptive illumination (I) above 0.1 cd/m2 increased the increment threshold (delta I) of the brushes between 407 and 515 nm about equally (delta I/I = 0.9). Comparison of the action spectrum of different photoreceptors with the spectral sensitivity of Haidinger's brushes suggested synergistic contributions of blue, green and red photoreceptors. A decrease in visual acuity to 0.01 by plus lenses did not affect the light threshold of the brushes significantly, while blurring by Bangerter foils increased the threshold markedly (about eightfold at visual acuity of 0.01). Thus, the determination of threshold of Haidinger's brushes provides the means of investigating certain macular functions behind, and widely independent of, opacities of the ocular media. While no retinal potentials (ERG) were seen during rotation of the polarizer, we obtained cortical potentials (VEP) closely related to the appearance of Haidinger's brushes in response to rotation onset of blue polarized light. The potential derived from Oz+Ol+Or consisted of a phasic negative response after a peak latency of 295 +/- 34 ms (N 295). Similar responses were also obtained to medium and long wavelengths (extrinsic windmill rotation during foveal fixation at stimulus conditions closely related to Haidinger's brushes: 3 degrees field, 2 cy/rev, 2 cd/m2, contrast 0.15). Thus VEP recording permits the comparison of entoptic and extrinsic excitation of the macula.

Adult↗
PubMed1994

[Amblyopic eyes produce an abnormal electroretinogram in pattern presentation with the on-off technique].

In amblyopic subjects the electroretinogram in response to pattern stimuli (P-ERG) has been variously described as normal or abnormal. While this was found with a reversing stimulus pattern, we presently recorded the P-ERG by exposing the eye to a checkerboard pattern (element size 10, 30, or 60 min of arc) alternating with a uniform field of equal mean luminance (5 or 500 cd/m2). Eight subjects with anisometropic or squint amblyopia and ten normal subjects took part in the investigation. No differences in P-ERG amplitudes were found in amblyopic eyes in response to pattern offset. However, the P-ERG to pattern onset was diminished in the amblyopic eyes compared with the healthy fellow eyes and with the eyes of normal subjects. Both the early positive (p-q) and the late negative (q-r) components of the onset response were affected. Furthermore, the normal amplitude profile of the onset response (largest response at 30 min, smaller responses at 10 and 60 min, i.e. pattern tuning) was lost in the amblyopic eyes. According to Arden [2] and Korth [9], the P-ERG in response to pattern onset represents the pattern component and that in response to pattern offset, the luminance component. From this we conclude that in subjects with anisometropic and squint amblyopia the retinal information processing of pattern stimuli is disturbed, whereas that for luminance discrimination remains normal.

Adolescent↗
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↗
PubMed1987

The electrical response of the human eye to patterned stimuli: clinical observations.

Following the first recording of electroretinographic responses in man to a barred pattern by Riggs and associates (1964) in normal and by Lawwill (1973, 1974) in clinical cases, the first striking observation of a complete loss of pattern electroretinogram (PERG) after injurious section of the optic nerve by Groneberg & Teping (1980) has led to the conclusion that the PERG originates from proximal retinal structures different from those responsible for the luminance electroretinogram (LERG). Typical changes of the PERG are seen during branch occlusion of the central retinal artery and vein. In ocular hypertension without visual field loss and glaucoma-related papillary changes the PERG is decreased at intraocular pressures above 26 mm Hg. In cases of primary glaucoma with regulated intraocular tension and without using miotics the amplitude of the PERG reflects the damage to the inner retinal layers. This favorably compares with the P100 latencies of the visual evoked cortical potential (VECP) which in primary glaucoma were partly within, partly outside the normal range. Other retinal diseases showing amplitude changes in the PERG are primary macular dystrophy, diabetic retinopathy, and the acute stage of optic neuritis. In all these cases the Ganzfeld LERG may be normal or nearly normal, whereas the PERG undergoes typical changes. On the contrary a highly preserved PERG can be recorded in cases of retinitis pigmentosa where the electrooculogram light rise and the LERG are already missing. In light of these findings the recording of PERG constitutes a new promising method of clinical electroretinography reflecting the activity of the hitherto omitted innermost retinal layers. It thereby contributes essentially to the location of disturbances within the visual system.

Electroretinography↗
PubMed1984

Area-luminance relationship for a constant light peak of the standing potential in the human eye.

The area-luminance relationship of the light peak of the slow oscillation of the standing potential was investigated in man by determining luminance response curves for field sizes between 5 degrees and Ganzfeld after dark adaptation and at two levels of adaptive illumination. The luminance necessary for a low constant light peak was read therefrom and related to the area stimulated. With foveally and extrafoveally centered test lights a straight line with gradient -1 was found if the logarithm of the threshold luminance was plotted against the log area of the field. This indicates that the threshold of the light peak of the standing potential is inversely proportional to its area.

Adaptation, Ocular↗