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Biomedical subjects

E Zrenner

Publications and source records attributed to E Zrenner.

249 records · Page 14Linked to original sources
PubMed1978

[The effect of the pupil as aperture and field stop on the various components of the human electroretinogram (author's transl)].

The electroretinogram (ERG) was recorded in 10 normal subjects under scotopic and photopic conditions with the pupil of one eye constricted and that of the other eye dilated. The human iris, being displaced from the nodal point of the eye, acts not only as an aperture, regulating the retinal illumination, but also as a field stop, limiting the visual angle, especially for large object fields, as in Ganzfeld illumination. This double effect of a constricted pupil clearly influences the Ganzfeld ERG, not only shifting the intensity response functions to higher luminances but also diminishing the maximal responses. Control experiments with smaller test fields, which are less affected by the pupillary field-stop properties, reveal no diminution of the scotopic b-wave amplitudes. Implicit time functions, being nearly independent of the number of receptors stimulated, can be matched by taking into account the pupillary diameter and calculating the actual retinal illumination (Troland). Amplitudes, being highly affected by a decrease of responding neurons due to the angle-limiting field-stop character of the pupil, cannot be matched with regard to the pupillary diameter. This effect is most noticeable in Ganzfeld illumination for the scotopic b-wave, generated mainly by neurons of the peripheral retina, and has less effect on the photopic responses that are generated more centrally.

Adaptation, Ocular↗
PubMed1978

Off-components in response to brief light flashes in the oscillatory potential of the human electroretinogram.

Amplitudes and implicit times of the several oscillatory potentials (OP's) in the human electroretinogram have been studied in relation to temporal, adaptive and spectral stimulus variables. The last of the OP-wavelets responds differently from the preceding ones; its implicit time shortens with increase in stimulus frequency or adaptive illumination, whereas that of the preceding OP's is prolonged or stays constant. Moreover, the last OP-wavelet is time locked with the stimulus offset, whereas the others are not. This can be confirmed by linear subtraction of responses to an isolated stimulus onset from responses to stimuli of variable durations. These results indicate, that the last oscillatory potential is related to the light offset and is presumably generated by the retinal off-elements described in single cell recordings.

Adaptation, Physiological↗
PubMed1976

[Electro-ophthalmological observations on the course of unilateral tapetoretinal degenerations (author's transl)].

A 32-year-old female patient suffering from a unilateral tapetoretinal degeneration for at least 7 years was investigated. The affected eye exhibits a typical fundus, concentric reduction of visual field, and a monophasic course of dark adaptation. The electroretinogram of the affected eye is extinguished; the electrooculogram does not show a light peak. The visual evoked cortical potential of both eyes shows a normal amplitude-stimulus intensity function. However, the first negative deflection exhibits a small difference of implicit time between the normal and affected eye. The normal eye does not show any pathological alteration.

Adult↗
PubMed1976

Visually evoked cortical potential (VECP) in dichromats.

The fundamental spectral sensitivity functions in man were studied by recording the visually evoked cortical potential (VECP). Using steadily presented strong blue-green and purple adaptation lights, two different spectral sensitivity functions were obtained with peaks in the green (540 nm) and in the red (590 nm) part of the spectrum. Only one peak (540 nm) was found in protanopia. The specific shift in deuteranopia and the influence of a blue-sensitive mechanism is discussed.

Color Vision Defects↗
PubMedDate not supplied

Clinical applications of pattern electroretinography: melanoma, retinal detachment and glaucoma.

A comparison between results obtained by pattern electroretinography (ERG), Ganzfeld cone and rod-ERG was made in 7 patients suffering from melanoma, glaucoma and retinal detachment. It was shown that the extent of the lesions, not seen ophthalmoscopically, can be well monitored by the second harmonic component of pattern electroretinography in cases where conventional Ganzfeld ERG's do not reveal defects. Especially damage caused by acute glaucoma attacks and those stemming from chronic hypertension can be well differentiated.

Acute Disease↗
PubMedDate not supplied

The effect of oral prednisolone on visual evoked potential latencies in acute optic neuritis monitored in a prospective, randomized, controlled study.

The Tübingen study of optic neuritis treatment was started in 1980 to apply new and sensitive tests for monitoring a potential therapeutical steroid effect on the course of acute optic neuritis. Visual evoked potentials were used to assess an effect of oral methylprednisolone in a randomized, controlled trial. Forty-eight patients with acute optic neuritis were treated orally either with methylprednisolone (100 mg per day initially, dosage reduction every 3 days; n = 15) or with thiamine (100 mg per day; n = 33) in the control group, 36 of them in a double-blind procedure. A comparison of the two treatment groups indicated that oral methylprednisolone resulted in a faster improvement in visual evoked potential latency in the initial phase (p = 0.015, 4 weeks after onset), but had no benefit after 12 weeks and 12 months. Follow-up showed different types of courses in the visual evoked potential latencies. The visual evoked potential latencies were correlated to other outcome variables, such as visual evoked potential amplitudes, visual acuity, Aulhorn flicker test and perimetry. We were able to handle nonmeasurable latencies in highly pathologic cases by means of ranks (taking into account censored observations).

Acute Disease↗
PubMedDate not supplied

Guidelines for basic pattern electroretinography. Recommendations by the International Society for Clinical Electrophysiology of Vision.

The pattern electroretinogram is a retinal response that can be evoked by viewing an alternating grating or checkerboard. It is receiving increasing clinical and research attention because it can provide information about inner retinal cells and the macula. However, clinicians may have trouble choosing between different techniques for recording the Pattern electroretinogram that have been described in the literature. The International Society for Clinical Electrophysiology of Vision has prepared guidelines for a basic pattern electroretinogram recording procedure to aid new users in obtaining reliable responses and to encourage more uniformity among existing users.

Electroretinography↗
PubMedDate not supplied

Electrophysiology in the investigation of acquired retinal disorders.

Electrophysiological research on acquired retinal disorders, both common and rare, is reviewed. Age is a major factor influencing electroretinogram (ERG) and electro-oculogram (EOG) findings. Bipolar or Müller cell death in the aging retina could account for much of the amplitude decline that is observed with age. In diabetic retinopathy, the oscillatory potentials can monitor the progression of the disease and indicate neuronal alterations rather than diabetic angiopathy of the retina. Human ERG studies on glaucoma concentrated on ERG measures that are dominated by inner retinal contributions. It has been shown that the pattern ERG can serve as a predictor of ocular hypertension's progression to glaucoma. In retinal disorders caused by endogenous intoxication, such as hepatic retinopathy, or exogenous intoxication from chronic lead exposure, ERG changes give an objective measure of the damage and allow to study the pathophysiological mechanisms that are involved. Inflammations of the choroid and the retina affect the standard ERG when they are diffuse. In central serous chorioretinopathy, functional disturbances can be revealed not only in the photoreceptors but also in the middle and inner retinal layers with the use of focal stimuli. Choroidal melanoma leads to large reductions of the EOG light peak-to-dark trough ratio through its influence on the transepithelial potential of the retinal pigment epithelium (RPE). In cancer-associated retinopathy, both the rod and cone ERGs are reduced. However, selective cone dysfunction has been described. In melanoma-associated retinopathy, the long flash ERG may reveal a specific pathophysiological mechanism, namely the affection of the ON-pathway with preservation of the OFF-pathway. ERG measurements can reveal vitamin A deficiency and are altered in cases with a mutation in the gene for the retinol binding protein in which other organs are not affected. Photochemical damage to the retina from light emission by the operating microscope can be assessed by electrophysiological methods.

Diagnosis, Differential↗
PubMedDate not supplied

Constant light affects retinal dopamine levels and blocks deprivation myopia but not lens-induced refractive errors in chickens.

Chickens were raised with either translucent occluders or lenses, both under normal light cycles (12-h light/12-h dark) and in constant light (CL). Under normal light cycles, eyes with occluders became very myopic, and eyes with lenses became either relatively hyperopic (positive lenses) or myopic (negative lenses). After the treatment, retinal dopamine (DA), DOPAC, and serotonin levels were measured by high-pressure liquid chromatography (HPLC-EC). A significant drop in daytime retinal DOPAC (-20%) was observed after 1 week of deprivation, and in both DOPAC (-40%) and DA (-30%) after 2 weeks of deprivation. No changes in retinal serotonin levels were found. Retinal DA or DOPAC content remained unchanged after 2 or 4 days of lens wearing even though the lenses had already exerted their maximal effect on axial eye growth. When the chickens were raised in CL, development of deprivation myopia was reduced (8 days CL) or entirely blocked (13 days CL). Lens-induced changes in eye growth were not different after either 6 or 11 days in CL, compared to animals raised in a normal light cycle. Thirteen days of CL resulted in a dramatic reduction of DA and DOPAC levels, but serotonin levels were also lowered. The results suggest that lens-induced changes in refraction may not be dependent on dopaminergic pathways whereas deprivation myopia requires normal diurnal DA rhythms to develop.

3,4-Dihydroxyphenylacetic Acid↗
PubMedDate not supplied

Evidence for calcium/calmodulin dependence of spinule retraction in retinal horizontal cells.

Horizontal cells of the carp retina alter their synaptic connections with cones during dark and light adaptation. At light onset, dendrites of horizontal cells, which are positioned laterally at the ribbon synapse, form "spinules," little processes with membrane densities. Spinules are retracted again during dark adaptation. Spinule retraction is also elicited upon glutamate application to the retina. In the present study, we address the question whether calcium/calmodulin-dependent pathways are involved in dark- and glutamate-evoked spinule retraction. Light-adapted retinas were isolated and subsequently dark adapted during incubation in media of different calcium concentrations. Spinule retraction was clearly blocked in low-calcium solutions (5 microM and 50 nM CaCl2). Incubation in medium containing cobalt chloride (2 mM) had the same effect. Both treatments blocked the glutamate-induced spinule retraction as well. These results indicate that spinule retraction is induced by a calcium influx into horizontal cells. To investigate whether calmodulin, the primary calcium receptor in eukaryotic cells, is present at the site of spinule formation, light- and dark-adapted retinas, embedded in LR White resin, were labelled with an antibody against calmodulin and gold-conjugated secondary antibodies. Horizontal cell dendrites at the ribbon synapse revealed strong calmodulin immunoreactivity, which was more than twice as high in light- as in dark-adapted retinas. The incubation of isolated retinas with the calmodulin antagonists W5 and W13 inhibited spinule retraction. In summary, these results suggest that spinule retraction may be regulated by calcium influx into horizontal cells and subsequent calcium/calmodulin-dependent pathways.

Animals↗
PubMedDate not supplied

Angiotensin II in the rabbit retina.

We investigated a putative local angiotensin II (AngII) system in the rabbit retina by examining AngII contents in the retina, vitreous humor, and choroid by radioimmunoassays and AngII synthesis in the retina and choroid by detection of angiotensin converting enzyme (ACE) mRNA. An antibody directed against AngII was used to localize possible cellular sources of AngII in the retina. To enhance immunoreactivity and to further examine AngII metabolism, tissues were preincubated in medium containing either protease inhibitors (PI), PI together with the AngII-precursor AngI, or PI and AngII. In some experiments the conversion of AngI to AngII was blocked by an ACE inhibitor. AngII concentration in the vitreous humor was only about 10% of the plasma concentration; in the retina and the choroid, however, AngII concentrations were 10 and 86 times higher, respectively, than in the plasma. ACE mRNA was present in both retina and choroid. Immunohistochemistry for AngII revealed faintly labeled amacrine cells at the inner border of the inner nuclear layer of the retina. Preincubation with PI resulted in an enhanced immunoreaction and in the labeling of fibers in the inner and outer plexiform layer; Müller cells and their processes as well as ganglion cells were now stained as well but the specificity of ganglion cell staining remains questionable. The immunoreaction was further enhanced when AngI or AngII was added to the incubation medium, whereas labeling totally disappeared when the conversion of AngI to AngII was blocked. No immunoreactive cells were detected in the choroid. In conclusion, the synthesizing enzyme for AngII is expressed in the retina and a specific AngII concentration is maintained there; AngII is localized in distinct cell types and can be metabolized within these cells. These data point to a local retinal AngII system that is protected and independent of blood-borne AngII.

Angiotensin II↗