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Biomedical subjects

E Zrenner

Publications and source records attributed to E Zrenner.

At least 163 records · Page 9Linked to original sources
PubMed1994

Dual rod pathways in complete achromatopsia.

The vision in typical complete achromatopsia is mediated only by rods. To provide more information about the physiological basis of this disorder, we investigated in a typical complete achromat the electrophysiological correlate of the psychophysically established 15-Hz-flicker nulling phenomenon. This phenomenon is believed to be the result of destructive interference between two independent rod pathways. We obtained dark-adapted Ganzfeld electroretinogram (ERG) recordings at 15 Hz with increasing stimulus intensities in the scotopic range and compared the results of the typical complete achromat with those of a normal observer. In both observers the 15-Hz ERG signal reached a minimum at retinal illuminances associated with the perceptual null and reversed in phase as the null was traversed. In comparison with the normal observer, however, the null in the achromat was found at higher scotopic retinal illuminances (ca. 0.4 log unit). Furthermore, the loss in amplitude associated with the null was much more evident, the decline in amplitude was steeper, and the phase shift of 180 degrees was accelerated.

Color Vision Defects↗
PubMed1994

Neuromodulatory effects of the renin-angiotensin system on the cat electroretinogram.

PURPOSE: Angiotensin-converting-enzyme (ACE) catalyses the formation of angiotensin II (ANGII), which presumably acts as a central neurotransmitter/modulator. ANGII-related effects have also been observed in the retina. Present in vivo experiments were designed to investigate further ANGII-related effects on retinal neuromodulation. METHODS: In 12 anesthetized cats, electroretinographic measurements were carried out in the dark-adapted state using corneal contact lens electrodes and a Ganzfeld stimulator. Quinapril was used to inhibit ACE. RESULTS: Reducing ANGII-concentration increased sensitivity (0.5 log units) and gain (50%) of the rod b-wave amplitude. The b-wave implicit time was stimulus dependent, shortening at high intensities. The scotopic threshold response and the oscillatory potentials were also influenced by ACE inhibition. However, a-wave and 30 Hz flicker remained unaffected. Effects of Quinapril on ERG-amplitudes were reversed by subsequent ANGII administration, except for the implicit time of the b-wave and scotopic threshold response. CONCLUSIONS: Although these results are accompanied by alterations in systemic blood pressure, several findings support the evidence that the renin-angiotensin system might have a neurophysiologic effect on retinal neurons outside the vascular system. These results are in accordance with immunohistochemical data found by others that point to angiotensinergic cell involvement and thereby further support the concept of angiotensinergic processes in the inner retina from a functional point of view.

Angiotensin II↗
PubMed1994

Angiotensin II-like immunoreactivity in the retina of some mammalian species.

The decapeptide angiotensin II (AngII) is a circulating hormone and the most important endogenous vasoconstrictor. In the central nervous system (CNS), AngII has been reported to have a transmitter-like function. In the retina angiotensin I (AngI), the precursor protein of AngII, and AngI-converting enzyme (ACE), the rate-limiting enzyme for AngII synthesis, are present. Both ACE inhibition and application of an AngII antagonist affect the b-wave of the electroretinogram. In the present study we used immunocytochemical techniques to identify putative AngII-containing cells in the bovine, cat, and rabbit retina. In the rabbit retina, faintly labeled amacrine cells were visible at the inner border of the inner nuclear layer. Preincubation with protease inhibitors (PI) resulted in an enhanced immunoreaction and in the labeling of ganglion cells and fibers in the inner plexiform layer. In the bovine retina, AngII-like immunoreactivity was detectable only after preincubation with PI. Under these conditions, ganglion cells and amacrine cells as well as cells in more distal parts of the inner nuclear layer were stained. In the cat retina, AngII-like immunoreactivity was detectable only after preincubation with PI and exogenous AngII. Photoreceptor and ganglion cells showed an enhanced AngII-like immunoreaction, and amacrine cells were stained preferably in clusters that were irregularly distributed within the retina. Our results demonstrate that AngII is a putative neurotransmitter in a subpopulation of mammalian amacrine cells.

Angiotensin II↗
PubMed1993

Standard for clinical electro-oculography. International Society for Clinical Electrophysiology of Vision.

The electro-oculogram is a widely used electrophysiological test, but recording techniques vary among different laboratories. This standard, approved by the International Society for Clinical Electrophysiology of Vision (ISCEV), describes simple technical procedures that will allow reproducible and comparable electro-oculograms to be recorded under a few defined conditions. The document is intended to improve the comparability of electro-oculographic data obtained throughout the world by guiding both clinicians and manufacturers, and the ISCEV recommends that future published reports indicate whether the recording technique meets the international standard.

Austria↗
PubMed1993

Impairment of retinal increment thresholds in Huntington's disease.

We have investigated detection thresholds for a foveal blue test light using a Maxwellian view system in 61 normal subjects, 19 patients with Huntington's chorea, 14 patients with Tourette's syndrome, and 20 patients with schizophrenia. Ten measurements were made: The blue test light (1 degree diameter, 500 msec duration) was presented either superimposed on a yellow adaptation field (5 degree diameter) or 500 msec after switching off this field (transient tritanopia effect). In both cases five different background intensities were presented. The only abnormality found was in patients with Huntington's chorea. During adaptation these patients' thresholds are significantly higher than normal (p < 0.005). No change was found in the transient tritanopia effect. Huntington's disease causes degeneration of several different transmitter systems in the brain. Increment threshold testing allows for noninvasive investigation of patients and confirms the involvement of the retina in the degenerative process in Huntington's chorea.

Adaptation, Ocular↗
PubMed1993

Experiences with the international standard for clinical electroretinography: normative values for clinical practice, interindividual and intraindividual variations and possible extensions.

The international Standard for Clinical Electroretinography requires a minimum of 5 standard response types. In a sample of 20 healthy subjects, the normative values according to this standard were established. Since the distribution of amplitude and implicit time does not follow a Gaussian distribution, we have found the median value and the 1st to 99th percentile or the 5th to 95th percentile useful for determination of abnormality, presented here separately for intraindividual and interindividual variation. To improve quality and reliability, we propose that individual laboratories extend the minimum standard and record the standard responses as parts of a stimulus series of increasing intensity. The normal value of the b/a ratio can easily be established from the maximum response to the Standard for Clinical Electrophysiology standard flash, pointing to abnormalities especially in circulatory disturbances and in degenerative diseases of the retina. The b/a ratio is between 1.5 and 1.7. If flicker responses are recorded at the 1st and 10th minutes after the onset of the rod saturating adaptation light (25 cd/m2), an increase in amplitude can be observed, which in our sample has a relative value of 1.3. A reduced increase in cone response amplitudes during light adaptation might point to abnormality within the rod/cone interaction. Responses from the cone system can be further differentiated by the use of chromatic stimuli. With appropriate filters, short-wavelength cone-sensitive and long-wavelength cone-sensitive responses can be differentiated also in clinical daily practice, which might be helpful for further differentiation of cone disorders. Regular measurements of intraindividual variability can help to improve the quality of electroretinogram recordings. Medians and ranges between the 1st and 99th and the 5th and the 95th percentiles were determined for all recordings for interindividual, as well as for intraindividual variations.

Adult↗
PubMed1993

Standard for clinical electro-oculography. International Society for Clinical Electrophysiology of Vision.

The electro-oculogram is a widely used electrophysiologic test, but recording techniques vary among different laboratories. This Standard, approved by the International Society for Clinical Electrophysiology of Vision (ISCEV), describes simple technical procedures that will allow reproducible and comparable electro-oculograms to be recorded under a few defined conditions. The document is intended to improve the comparability of electro-oculogram data obtained throughout the world by guiding both clinicians and manufacturers, and ISCEV recommends that future published reports indicate whether the recording technique meets the international Standard.

Calibration↗
PubMed1993

[Clinical electroretinography: standard protocol and normal values].

The International Standard of Clinical Electroretinography serves as standard protocol for recording electroretinographic responses in order to facilitate worldwide comparisons of examinations. To promote its distribution and acceptance throughout the German speaking countries, we established normal values for the five standard responses and added a German translation of the International Standard in the appendix. To determine normal values for electroretinographic data we suggest to use percentiles instead of parameters based on a Gaussian distribution. Patient-related (age, sex) and -unrelated (interstimulus-interval, diurnal rhythm) parameters proved to influence the data values significantly. With these variables taken into account one can increase the clinical value of electroretinography in terms of a greater reliability and predictiveness of data.

Adolescent↗
PubMed1993

[Visual compromise of automobile drivers by frontal photo-flash in mesoptic conditions].

The time for recovery of recognition of an optotype presented at a distance of 40 m subsequent to exposure to a flash gun (Eso company, Tettnang; flash energy 200 Ws, duration 1/1000 s; distance 10 m) was studied on 97 subjects aged 20 to 83 years. A Landolt-ring (contrast 1:5, diameter 29 cm), mounted on a disk (diameter 58 cm) which could be rotated in steps of 45 degrees served as a test target. The flash gun could be dimmed down by a red filter (Schott RG 665). The tests were performed at night without additional illumination except the low beam of the car. The flash gun was foveally fixated. After a white flash, a period of 93.1 s +/- 48.6 s (MEAN +/- SD) passed before the optotype could be recognized correctly again. By adding the red filter in front of the flash gun the recovery time could be shortened significantly (p < 0.0001; Wilcoxon signed-rank test) to 4.9 s +/- 1.7 s. "Time for re-adaptation" after dazzling by red flash is comparatively short and therefore strongly influenced by many variables (e.g. time for recognition and for verbalization). Because of that a final evaluation of dazzling by red flash seems to be impossible with this method. Subjects of advanced age and opacities of the ocular media showed an increase in the "time for re-adaptation" for the white as well as the red flash. In conclusion, a speed control using white flash guns at night can be considered as critical.

Adult↗
PubMed1993

[Developments in ophthalmologic electrophysiology].

During the last years electrophysiology in ophthalmology has been facilitated to a big extent by computerized methods. Thus it has become a suitable method for an increasing number of relevant diagnostic problems. To make comparisons between test results of different diagnostic places easier an international standard concerning the methodology of the electroretinogram (ERG) has been elaborated by the "International Society of Clinical Electrophysiology in Vision" (ISCEV). Aim of the present article is to give a short description of the ERG-standard and to review recent developments in clinical electrophysiology in ophthalmology (ca. since 1989).

Adult↗
PubMed1993

[Immunohistochemical studies of the role of dopaminergic retinal cells in neuronal light adaptation].

BACKGROUND: Tyrosine hydroxylase (TH) like immunoreactivity was investigated in frozen sections and in whole mounts of the chicken and bovine retina in order to investigate the distribution and role of dopaminergic structures in retinal circuiting. METHODS: By means of monoclonal antibodies against tyrosine hydroxylase the dopaminergic retinal structures were marked and their distribution determined by light microscopy. RESULTS: In both species TH-positive labelled cell bodies were localized in the innermost part of the inner nuclear layer (INL) close to the inner plexiform layer (IPL). In addition, in bovine retina TH-positive cell bodies were also located in the IPL and in the ganglion cell layer. TH-positive cell bodies gave rise to one to four fibers, which extended into sublayer 1 of the inner plexiform layer. In this sublayer fine fibers with button like structures were visible establishing a dense TH-positive plexus. In both species within this plexus small spots, free of any staining and surrounded by a ring of TH-positive fibers, could be observed. These "ring-like" structures were twice as frequent in bovine than in chicken retina. One to three thicker fibers per cell project into sublayer 3 and 4-5 of the IPL. In sublayer 3 of chicken retina they ramified into very long and fine fibers with small "bouton" like knobs. In bovine retina similar long fine fibers are found predominantly in sublayer 4-5. In sublayer 4-5 of the chicken retina the fibers were short and thick and shows a clear ramification pattern. They were found to be in close contact to the fibers of adjacent TH-positive cells. In bovine retina thin fibers arose from the TH-positive plexus in sublayer 1, passed through the INL and ramified within the outer plexiform layer (OPL). In chicken retina fibers only occasionally entered the INL; in the OPL fibers never could be observed. The appearance of TH-positive cells in the bovine and chicken retina resembles that of TH-positive cells found in other vertebrates. In whole mounted retinae from chicken and bovine the mean-density of TH-positive cells was 23 cells/mm2 and 27 cells/mm2, respectively. CONCLUSIONS: The fact that in the rod dominated bovine retina dopaminergic "ring-like" structures are observed more frequently than in the chicken retina may give a morphological hint that dopaminergic amacrine cells might be involved in neuronal retinal light adaptation.

Adaptation, Ocular↗
PubMed1993

Inter-individual variability in the dynamics of natural accommodation in humans: relation to age and refractive errors.

1. To study the relationship between accommodation under natural viewing conditions, age and refractive errors, we have measured time courses of accommodation in thirty-nine human subjects aged 5-49 years using a newly developed technique. The technique is based on infrared photoretinoscopy and involves fully automated on-line image processing of digitized video images of the eyes with a sampling rate of 5.3 Hz. 2. The distance between the subject and the video camera was about 1.3 m. Head movements of the subject required little restriction because the eyes were automatically tracked in the video image by the computer program. All subjects were tested under binocular viewing conditions. 3. Both refraction of the right eye and pupil diameter were measured with a precision of 0.2-0.4 dioptres (D) and 0.1 mm, respectively, and were plotted on-line. The data were subsequently automatically analysed. 4. Automated infrared photoretinoscopy proved to be very convenient and easy to handle in both children and adults. 5. The maximal speed of accommodation for a target at a distance of 5 D declined in the subjects with age (from up to 21.7 D s-1 for accommodation and 32.7 D s-1 for subsequent accommodation to a distant target ('near to far accommodation') in children down to 2-18 D s-1 in adults). There was a striking inter-individual variability in the maximum possible speed of accommodation and near to far accommodation. 6. Speed of accommodation and of near to far accommodation was correlated for each subject. However, in most of the subjects, the process of near to far accommodation was faster than accommodation (P < 0.005, if averaged over all subjects). This correlation was independent of age. 7. The accommodation-induced pupillary constriction (pupillary near response) was absent in children for a 4 D target; even at 10 D, there was no reliable pupillary response. The pupillary near response increased to about 1.6 mm D-1 of accommodation at the age of 47. Since a pupillary near response could still be elicited in presbyopic subjects unable to accommodate, the ratio of pupillary constriction per dioptre of accommodation approached infinity. 8. The magnitude of the pupillary near response was highly variable even among subjects of the same age but was typical for each subject. There was a correlation (P < 0.01) to refractive error: corrected myopes had weaker pupillary near responses than emmetropes or hyperopes.(ABSTRACT TRUNCATED AT 400 WORDS)

Accommodation, Ocular↗
PubMed1993

Differences in adaptation between on- and off-centre ganglion cells and rod-mediated cone sensitization in cat retina.

1. Response properties of on- and off-centre retinal ganglion cells were investigated in cats. The stimulus parameters were selected so as to demonstrate interactions between the rod and the cone systems. 2. Response versus log stimulus intensity (R-log I) functions were determined for the receptive field centres while both test stimulus irradiance and the background illumination were varied over a range up to 7 log units. In order to determine the course of adaptation to chromatic stimuli, threshold versus intensity (t.v.i.) functions were measured over a wide range of adaptation levels. 3. An increase in background illuminance produced a shift of the R-log I functions to higher irradiances of test stimuli in most ganglion cells, indicating a desensitization of the centre response in the presence of background lights. Using test stimuli which most efficiently stimulate the rods (501 nm), clear differences could be seen in the adaptation behaviour of on- and off-centre ganglion cells. Chromatic backgrounds (blue-green and orange) reduced the responses of off-centre cells more than those of on-centre cells (the difference between them amounting to as much as 2 log units). Simultaneously, equivalent t.v.i. functions had significantly steeper slopes (0.94 and 1.1) in the linear proportions of off-centre cells compared to on-centre cells (0.76 and 0.75) under light levels mediated by rods. Such differences were not observed when a test stimulus of 575 nm was used which resulted primarily in stimulating the long-wavelength cone (L-cone) system. 4. In a subpopulation of off-centre cells (20% of the total number of off-centre cells recorded), a strikingly different adaptation behaviour was observed. Here, the presentation of a dim short-wavelength background produced a shift of R-log I functions to lower test stimulus irradiances. The receptive field centre became even more sensitive, by up to 1.5 log units, in the presence of dim adapting backgrounds rather than in the dark-adapted state. Accordingly, the t.v.i. function did not increase monotonically but showed a 'dip' in the presence of dim backgrounds. Only at photoic levels, the t.v.i. functions revealed a response behaviour similar to the other ganglion cells. The sensitization with dim backgrounds was only observed in the case of test stimuli designed to stimulate the cone system (575 nm) and in the presence of a rod-adapting blue-green background.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1993

Ocular findings in a family with autosomal dominant retinitis pigmentosa and a frameshift mutation altering the carboxyl terminal sequence of rhodopsin.

A family is described in which an 8 base pair deletion (nucleotides 5252-5259, codons 341-343) of the rhodopsin gene cosegregates with autosomal dominant retinitis pigmentosa (adRP). The deletion results in a shift in the reading frame, causing a rhodopsin molecule extended by one residue and substantially altered at the carboxyl terminus. Phenotypic expression is relatively mild. In affected members, night blindness did not occur before the age of 16, and late onset of visual field loss was consistently reported. Even older individuals (59 and 76 years) had preserved central islands in the visual field; a younger female patient had normal visual fields until the age of 34. ERG and psychophysical tests showed well preserved cone function at stages of virtually abolished rod function. Phenotypic differences and similarities between this form of adRP and others associated with mutations at the carboxyl terminus of the rhodopsin molecule are discussed. The cause of RP by mutations in this region remains to be clarified.

Adult↗
PubMed1993

Genetic heterogeneity among blue-cone monochromats.

Thirty-three unrelated subjects with blue-cone monochromacy or closely related variants of blue-cone monochromacy were examined for rearrangements in the tandem array of genes encoding the red- and green-cone pigments. In 24 subjects, eight genotypes were found that would be predicted to eliminate the function of all of the genes within the array. As observed in an earlier study, the rearrangements involve either deletion of a locus control region adjacent to the gene array or loss of function via homologous recombination and point mutation. One inactivating mutation, Cys203-to-Arg, was found in 15 probands who carry single genes and in both visual pigment genes in one subject whose array has two genes. This mutation was also found in at least one of the visual pigment genes in 1 subject whose array has multiple genes and in 2 of 321 control subjects, suggesting that preexisting Cys203-to-Arg mutations constitute a reservoir of chromosomes that are predisposed to generate blue-cone-monochromat genotypes by unequal homologous recombination and/or gene conversion. Two other point mutations were identified: (a) Arg247-to-Ter in one subject with a single red-pigment gene and (b) Pro307-to-Leu in one subject with a single 5' red-3' green hybrid gene. The observed heterogeneity of genotypes points to the existence of multiple one- and two-step mutational pathways to blue-cone monochromacy.

Base Sequence↗
PubMed1993

Uncommon chiasmal lesions: demyelinating disease, vasculitis, and cobalamin deficiency.

We report on eight patients who presented for evaluation of unexplained visual loss. They all showed a typical chiasmal visual field defect (bitemporal hemianopia, junction scotoma). In all patients, high-resolution computer-assisted tomographic (CT) scans of the sellar region were normal, and neither the medical history nor additional ophthalmological findings pointed to any explanation for the underlying disease. Six patients seemed to have suffered from chiasmal optic neuritis. Magnetic resonance imaging (MRI) scans could elucidate the diagnosis in five cases: white-matter lesions typical of multiple sclerosis (MS) were found and, additionally, in four cases an enlargement of the chiasm or barrier defect was revealed in post-gadolinium MRI. In one patient, MRI was normal. He recovered completely after megadose steroid therapy. One patient developed motoric symptoms of MS during the following year, another patient had mild sensory symptoms and recurrence of severe optic neuritis. An MR-proven chiasmal lesion due to a leukocytoclastic immunovasculitis combined with small subcortical white-matter lesions was diagnosed in another patient. The field defects disappeared spontaneously. In a 28-year-old woman a low vitamin B12 level was found in routine blood samples. Parenteral vitamin B12 substitution led to an almost complete recovery of the visual field defects. Chiasmal optic neuritis may occur isolated or during the course of MS. Megadose steroids may be of value if contraindications have been ruled out. A chiasmal visual field defect caused by vitamin B12 deficiency is very uncommon. A similar case was reported in 1961.

Adult↗
PubMed1993

Clinical findings in patients with congenital stationary night blindness of the Schubert-Bornschein type.

We examined 23 patients (18 families) with congenital stationary night blindness (CSNB) who showed a "negative" electroretinogram of the Schubert-Bornschein type. The goal of the study was to find evidence for the classification proposed by Miyake (complete and incomplete type) based on electroretinograms (ERGs) and dark-adaptation function and to look for additional classification parameters that argue for or against heterogeneity. In all, 13 patients revealed the complete type and 10 the incomplete type. The mean age of our patients was 24.7 years (median, 21 years; SD, 14.5 years). In both groups, almost all patients were myopic (mean, -6.05 D; SD, 3.77 D; median, -6.12 D), and there was a reduction in visual acuity (mean, 0.34; SD, 0.14; median, 0.35) without significant differences between the subgroups. In all, 56.5% of the patients suffered from nystagmus and 52.2% squinted. These results confirm the Miyake classification and suggest that only ERG and dark-adaptation data allow a discrimination between the two subtypes. The ongoing molecular analysis will show whether there are correlates on the molecular level.

Adult↗