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R Rix

Publications and source records attributed to R Rix.

At least 19 recordsLinked to original sources
PubMed1992

The different contributions of local luminance decreases and increases to the pattern electroretinogram (PERG).

The typical pattern-onset-offset stimulus (stimulus A) consisting of local luminance increases and decreases was broken down into stimuli presenting only local luminance increases (stimulus B) or only local luminance decreases (stimulus C). With stimulus B the onset ERGs are luminance responses. With stimulus C the onset ERGs are pattern-related responses showing a spatial band-pass function. With stimulus A the response is a linear addition of responses to stimuli B and C. The simultaneously recorded VEP is a pattern-related response with all three stimuli (A-C).

Contrast Sensitivity↗
PubMed1990

On the time course of retina damage and regeneration after intravenous application of vincristine as monitored by visual light response.

The alkaloid vincristine is used for the chemotherapy of tumours in man. In rabbits and rats it is known to cause alterations in the retina, such as a globular deformation of the photoreceptor outer segments. The electroretinograms of human patients treated with vincristine of an equivalent dose, however, did not indicate considerable retina destruction as had been anticipated. In order to explain this discrepancy a comprehensive study was performed using the retina of albino rats which is electrophysiologically very well characterized. After vincristine injection, electron micrographs of the retina as well as extracellular recordings of its electric activity dependent upon the time p.i. consistently showed that transient retinal defects appeared in a mosaic-like distribution. Small areas completely degenerated and did not show any electric activity whereas other areas were normal. Therefore, transretinal measurements such as the electroretinogram should represent an average effect of the electric response of the retina. Half-life time for development of the maximum vincristine effect was 50 h whereas the regeneration of a full electrophysiological photo response was obtained in a further 70 h. The vincristine effect could be used as a model for the generation of some retinal diseases.

Animals↗
PubMed1989

Differences between pattern onset and pattern reversal retinal responses.

The pattern-evoked electroretinogram was recorded to pattern onset-offset and pattern reversal stimuli in two color-normal subjects with either luminance contrast of black-red (600 nm) and black-green (526 nm) square-wave stripe patterns or color contrast red-green patterns. The size of the onset response shows a spatial tuning with luminance contrast patterns and only a simple low-pass filter function with color contrast patterns. The peak latency of the response to luminance contrast increases with increasing spatial frequency but stays constant with color contrast patterns. The size of the reversal responses, however, shows only a low-pass filter function under both contrast conditions. The peak latency to luminance contrast shows a slight increase and to color contrast it remains constant with increasing spatial frequency. The differences noted under the various stimulus conditions must take into account the possible effects of different luminance modulation depths of onset and reversal stimuli, the modulation transfer function of the eye, and the activity of luminance-antagonistic and color-antagonistic receptive fields.

Color Perception↗
PubMed1988

Electrical responses of the human eye to changes in saturation of the stimulating light.

Previous studies on color vision using the electroretinogram or the evoked potential have concentrated only on brightness and hue but not on the saturation of color. In the present investigation patterns of alternate stripes of a highly saturated color and a totally desaturated color (= white) of equal brightness were presented in the pattern-reversal mode. It can be demonstrated that the reading obtained is in agreement with psychophysical saturation scale data of earlier investigators.

Color↗
PubMed1988

Luminance-contrast evoked responses and color-contrast evoked responses in the human electroretinogram.

Pattern electroretinograms to onset-offset stimuli were studied in response to luminance-contrast (e.g. red-black or green-black) and color-contrast (e.g. red-green) stripe patterns of equal luminance. Onset responses to color-contrast patterns show no spatial selectivity and a constant peak latency at all spatial frequencies, a behavior different from that of luminance-contrast evoked responses (spatial selectivity and increasing peak latency with spatial frequency). These results are tentatively related to the physiology of tonic and phasic primate retinal ganglion cells and to the spatially selective and non-selective human contrast sensitivity to respectively luminance-contrast and color-contrast gratings.

Color Perception↗
PubMed1987

The pattern ERG in response to colored stimuli.

The pattern-evoked electroretinogram (PERG) was studied in response to square-wave stripe patterns contrasting either between dark and colored stripes ("red-black" or "green-black" luminance contrast pattern) or between the two colors (red-green chromatic contrast pattern). All lights were matched in photopic luminance. A two-channel Maxwellian view system was used to present the stimuli in the onset-offset mode. When no pattern was present a mixture of both colors was seen. Different spatial frequencies were studied and the amplitudes of the onset response were evaluated. When the two luminance contrast patterns were presented, the responses showed a spatial selectivity. However the combination of the two colors (red-green contrast) resulted in a monotonic decrease of the response with spatial frequency. The spatially selective behavior of the response to luminance contrast patterns could be associated with the on-off center-surround organization of retinal receptive fields. The behavior of the response to chromatic-contrast patterns, on the other hand, could be explained by the action of color-opponent center-surround receptive fields as described in the primate.

Color Perception↗
PubMed1985

Changes in spatial selectivity of pattern-ERG components with stimulus contrast.

Electrical mass responses of the visual system to stripe patterns of varying fineness (spatial frequency) can show either an amplitude maximum at a medium spatial frequency, a behavior termed "spatial selectivity," or a monotonic decrease in amplitude with increasing spatial frequency. The former behavior is probably mediated by neurons having a center-surround receptive field structure and the latter by neurons lacking this antagonism. The pattern-evoked human electroretinogram was studied in this report using different spatial frequencies and pattern contrasts. The positive component of the response showed a spatial selectivity only at low contrast but was not spatially selective at the highest contrast. The negative component showed a spatial selectivity at all contrast levels. The data indicate that if pattern-related responses activated by antagonistic receptive fields are to be studied, low contrast values should be employed and attention should be paid to the negative component of the response.

Electroretinography↗
PubMed1985

Spatial contrast transfer functions of the pattern-evoked electroretinogram.

Pattern ERGs in response to pattern-reversal stimuli varying in spatial frequency (range: 0.2-9.03 cycles/deg) and contrast (range: 0.03-0.93) were recorded from two normal male subjects. At most spatial frequencies the response amplitude increased linearly up to the highest contrast without saturation. From the amplitude-versus-contrast plots spatial contrast-transfer functions were derived for different levels of contrast. The sensitivity of the reversal response showed a spatial selectivity around 4 cycles/deg, which was more pronounced at low, rather than at high, contrast values. Good agreement with the psychophysical contrast-sensitivity curve was found. The procedure described permits a quantitative analysis of the sensitivity of the retina to spatial contrast stimuli and could be helpful in the diagnosis of diseases of the eye and the optic nerve.

Electroretinography↗
PubMed1979

[Changes in the outer plexiform layer of the rabbit retina after long-term application of vincristine].

Rabbits which had been intravenously injected with Vincristine for six weeks showed changes in the outer plexiform layer of the retina after one year, which suggests the destruction of receptor cells, bipolar ganglion cells, and horizontal cells. Compensated cell damage accompanied by loss of microtubuli in the cytoplasma, autolytic vacuoles, granular material deposits, and membrane changes of the ribbon complex were frequently observed. A comparison between axons and dendrites showed a predominance of damaged dendritis over axons. Because short-term studies have not produced the same results, different regeneration capacities, which might have their origin in the endoplasmatic reticulum, are discussed.

Animals↗
PubMed1979

[The influence of vigilance on DC response in human visual evoked potential (author's transl)].

Visual evoked cortical potentials elicited by long-lasting stimuli of red light were examined in eight subjects under different conditions of vigilance. The DC components of the evoked potentials were compared with the delta and theta activity (0-7.5 Hz) of the EEG by means of frequency power spectra. The results are: 1) A proportional relationship exists between the amplitude of the negative DC component of the evoked potential and the theta and delta activity in the EEG. 2) Under conditions of low vigilance the negative DC potential does not return immediately to the baseline after the off-effect. Instead it may reach a second peak. 3) Under conditions of high vigilance, the DC potential may reverse its polarity. Its return to the baseline following the off-effect is immediate. 4) No dependence of the cortical DC potential on the intensity of the light stimulus could be demonstrated. 5) Since the negative potential outlasts the visual stimulus and could be recorded at the occiput and the vertex, it may be regarded as a nonspecific arousal reaction. Furthermore, since the positive DC potential can only be recorded at the occiput, it is regarded as a specific stimulus-correlated response.

Adult↗
PubMed1978

[Hydroxychinoline- and zinc-treated acrodermatitis enteropathica and electroretinographic findings (author's transl)].

A meanwhile 13 years old boy had to be treated by hydroxychinolines for a severe acrodermatitis enteropathica since his 1st year of life. At the age of 5 years he showed visual deterioration by atrophia optici. Dose reduction and application of different halogen substitutions were tried. Finally, it was daily oral zinc application and continuous control of the serum zinc level which made disappear all cutaneous and mucous symptoms. At an unchanged ophthalmoscopic status, there occurred a slight raise of vision, an enlargement of peripheric campus and a normalization of the electroretinographic potentials.

Acrodermatitis↗
PubMed1978

[Retinographic alterations in different forms of congenital cataracta (author's transl)].

In a follow-up study of patients suffering from congenital cataract, particular attention was paid to the electroretinogram. Besides hereditary lens opacifications and rubella embryopathy, galactosaemia and spontaneous idiopathic hypoglycemia occurring in children and infants were examined. The question, how much biochemical factors can influence the ERG, is becoming more important.

Cataract↗
PubMed1977

[The D.C. response in the human electroretinogram under different degrees of wakefulness (author's transl)].

A report is given on the D.C. component of the human ERG following stimulation with red light of varying intensities and under different conditions of vigilance. The degree of the subject's wakefulness can be followed by looking at certain frequency components of the power spectrum of the occipital EEG. 1. The ERG remains uninfluenced by the degree of the subject's vigilance. 2. Red light is especially suited for eliciting separately photopic an scotopic responses in the on-effect of the ERG, possibly in the off-effect also. The D.C. potential is regarded as a component of the scotopic b-wave. The photopic x-wave can be recorded with very low stimulus intensities and stays clearly separated from the D.C. component.

Electroretinography↗
PubMed1976

[A histological and electron microscopic study of the rabbit retina after application of vincristin (author's transl)].

Temporary electrophysiological damage to the rabbit eye proportional to dosis and application time was observed after application of Vincristin (Lilly). Cell destruction in all retinal layers was observed upon histological and electron microscopic examination of the animals. The outer segments of the receptor cells showed chiefly diffuse damage, and the pigment epithelial cells showed a high incidence of reorganization. Follow-up examination one year later showed this damage to be partially reparable, especially when very high doses had not been applied. Regeneration of the outer segments was observed. Destruction through pyknosis of the nucleus and cytoplasmal destruction was observed in a small number of receptor cells, bipolar ganglion cells, and ganglion cells. This also explained the absence of lasting functional abnormalities in the ERG and EVP.

Animals↗