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E Zrenner

Publications and source records attributed to E Zrenner.

At least 145 records · Page 8Linked to original sources
PubMed1995

The renin-angiotensin system--a possible neuromodulator in the human retina?

Morphology studies imply a possible contribution of the renin-angiotensin system (RAS) to neurotransmission in the mammalian retina. To investigate further the functional role of the RAS in the visual system of humans, we tested the effects of the angiotensin-converting enzyme (ACE) inhibitor Captopril (Capt; 25 mg) on electroretinogram (ERG) recordings, the cone flicker threshold (CFT), the FM-28-HUE test, and the psychophysical rod threshold in healthy volunteers. The parameters of renin, angiotensin, and blood pressure were controlled. We obtained the following results. First, Capt induced a significant decrease in amplitudes of the scotopic b-wave, oscillatory potentials, and the a-wave. The latency of responses to 30-Hz flicker was increased. Second, the CFT was reduced to a lower intensity, whereas the final rod threshold remained unchanged. These results are in accordance with previous immunocytochemical and electrophysiological data. They cannot be explained exclusively by the observed changes in systemic blood pressure. We conclude that the RAS may possibly be involved in retinal neurotransmission in humans in addition to its vascular effects.

Administration, Oral↗
PubMed1995

[Disorders of color perception and increase glare sensitivity in phenytoin and carbamazepine therapy. Ocular side effects of anticonvulsants].

Advanced psychophysical tests, performed in 42 epileptic patients, show that the antiepileptic drugs phenytoin and carbamazepine can specifically affect the retinal function, while Valproic Acid and the epileptic seizures do not. The Farnsworth-Munsell 100-Hue and Panel D-15 désaturé tests revealed an accumulation of errors along the tritan/tetartan axis (blue colour vision deficiencies) and a high total error score. The same defect was shown by measurement of the spectral sensitivity functions. The results obtained for mesopic vision and especially glare sensitivity measured by nyktometry were markedly affected in these patients compared to a normal population. The enhanced sensitivity to glare is mainly the only one symptom complained by the patient. We propose a screening method for early detection of phenytoin- and carbamazepine-induced neurotoxicity. The literature of ocular side effects of anticonvulsant drugs is carefully reviewed.

Adolescent↗
PubMed1995

[Correlation between clinical and molecular genetic findings in Leber's optic atrophy].

Leber's hereditary optic neuropathy (LHON) is associated with point mutations of mitochondrial DNA (mtDNA) that appear to be pathogenetic for this disease. These mutations affect nucleotide positions 3460, 4160, 11,778, 14,484, and possibly 15,257. The pathogenetic significance of other mtDNA point mutations (secondary mutations) is less clear. We reviewed the clinical and molecular genetic characteristics of 29 visually symptomatic patients from 26 families. In addition, we studied 54 relatives of the maternal line of these patients. Sixteen of them underwent clinical and molecular genetic examination; 38 underwent only molecular genetic examination. The 29 affected individuals showed a male predominance of 93.1% (27/29) and ages of onset of visual loss ranging from 15 to 55 years. The time interval between affected eyes was never longer than 1 year. Tobacco and/or alcohol abuse was common. Peripapillary microangiopathy was found in 20.7% (6/29) of our patients. The number of patients with peripapillary microangiopathy seems to be small, but we could not examine all patients early after onset of the disease: the time of first examination is critical for the diagnosis of peripapillary microangiopathy. From the 16 relatives who underwent clinical examination, 62.5% (10/16) also had peripapillary microangiopathy. Eighteen patients were analyzed by brain computed tomography or magnetic resonance imaging. Four definitely pathological results seem remarkably high in comparison with the results of other authors. Our LHON patients and their relatives invariably had an identical pattern of point mutations, both primary as well as secondary. Of the LHON patients, 79.3% had the primary mutation at position 11,778, 20.7% at position 3460. Different numbers and combinations of secondary mutations were observed in a large portion of both groups. Three patients with the 11,778 mutation noticed remarkable visual recovery. There was no clear correlation between the type and number of point mutations in the individual and the severity of the disease.

Adolescent↗
PubMed1995

Centrally tinted contact lenses. A useful visual aid for patients with achromatopsia.

Achromatopsia (rod monochromacy) is a congenital color-vision defect of autosomal recessive inheritance due to severely abnormal or totally absent cone function. The disease is characterized by markedly reduced visual acuity, nystagmus, and, often, ametropia. Even under normal daylight conditions, these patients are extremely handicapped by glare because of a lack of rod inhibition by the abnormal or deficient cones. Light-absorbing glasses (absorption > 90%) can ameliorate this visual impairment to a certain extent but are sometimes not accepted by the patient since they are felt to disfigure the face. Especially during the first few years of school, this can lead to psychological problems. A special contact lens (Hydroflex, Wöhlk Company, Kiel) with a centrally tinted area (absorption 80%) that is slightly greater in diameter than the pupil under daylight conditions can correct ametropia and reduce light exposure and dazzle in a cosmetically much better way. Our first experience with this kind of visual aid in a 9-year-old girl suffering from incomplete achromatopsia is presented.

Child↗
PubMed1995

Ethambutol alters spinule-type synaptic connections and induces morphologic alterations in the cone pedicles of the fish retina.

PURPOSE: Ethambutol can cause optic neuropathy and deficiencies in color-opponent visual processing in patients treated for tuberculosis. In fish, Ethambutol induces color vision deficiencies similar to those observed in humans and affects color coding in retinal ganglion cells. Color opponency in fish is mainly mediated by a horizontal cell feedback onto cones thought to be provided by spinules. The authors examined whether Ethambutol affects spinules and is, therefore, able to alter color processing at a distal stage, that is, at the first synaptic connection within the retina. METHODS: Ethambutol was injected into the vitreous of either dark- or light-adapted fish. After drug application, fish were held under different illumination conditions. Thereafter, the retinas were dissected and prepared for electron microscopy. Ultrathin tangential sections of retinas were examined at the level of the outer plexiform layer. RESULTS: In already light-adapted retinas, a high dose of Ethambutol (10 mM) reduced the number of spinules by 30%. Ethambutol application in the dark with subsequent light adaptation resulted in severe dose-related inhibition of light-induced spinule formation. In these experiments, low doses (0.1 mM) of Ethambutol caused 40% inhibition, and high doses (10 mM) caused 70% inhibition. Besides affecting spinules, Ethambutol occasionally induced a degeneration of cone pedicles. This neurotoxicity only occurred in cones exposed to light. CONCLUSIONS: Results show that Ethambutol alters synaptic connections between horizontal cells and cones in a dose-related fashion; Ethambutol treatment can be toxic for cone pedicles and can cause their degeneration; and the rod pathway is not affected by the drug. This indicates that Ethambutol influences the color-coding process already at the level of the cone-horizontal cell synapse.

Animals↗
PubMed1995

[Sensitivity and specificity of masked field campimetry].

Patients with circumscribed visual field defects are able to perceive the scotomata immediately while looking at randomly distributed black and white squares (12' x 12') flickering on a VDU with a high frequency (approximately 30 Hz), resulting in a stimulus field comparable to the white-noise field on a TV screen without reception. In 368 eyes of 368 patients with varying lesions of the visual pathway the results of white-noise field campimetry were compared with those of conventional threshold-related, slightly suprathreshold automated grid perimetry. Rate of detection (sensitivity) was 84.2% in conventional perimetry and 80.7% in white-noise field campimetry, respectively. The results are not significantly different (p > 0.1; McNemar test). Examinations in 198 eyes of 198 persons without any indication of a visual pathway defect allowed a definition of the normal range of white-noise field campimetry to be made. The specificity of this new method was 82.3%. The outcome of this most extensive study on sensitivity and specificity of noise field campimetry is compared with other publications. The results presented emphasize the capabilities of this new method as a screening test. They encourage the initiation of a field study using the noise field stimulus broadcasted to home TV sets.

Adolescent↗
PubMed1995

[Sensitive physiologic perceptual tests for ocular side effects of drugs exemplified by various anticonvulsants].

Advanced psychophysical tests, performed in 42 patients who have seizures, showed that the widely used antiepileptic drugs, diphenylhydantoin and carbamazepine, can specifically affect retinal function, while valproic acid and the epileptic seizures do not. The Farnsworth-Munsell 100-Hue and Panel D-15 désaturé tests revealed an accumulation of errors along the tritan/tetartan axis and a high total error score. As shown by measurement of the so-called transient tritanopia and by determination of the spectral sensitivity, this blue vision defect is not only due to loss of postreceptoral interaction between long- and short-wavelength-sensitive cones, but is also based on a disturbance in the receptor mechanism itself. The dark adaptation curve was not affected. As determined by cone flicker thresholds during dark adaptation, the inhibitory action of rods on cones is reduced. The results obtained for mesopic vision and especially glare sensitivity measured by nyktometry were markedly affected in these patients compared to the normal population. The psychophysical methods provide a very sensitive test for early detection of drug-induced retinal dysfunction and allow clear differentiation between the loss of a receptor mechanism and a defect in the neuronal interaction between photoreceptors in the human visual system induced by antiepileptics.

Adolescent↗
PubMed1995

[Social ophthalmologic aspects of retinitis pigmentosa].

Inherited retinal degenerations cause severe visual handicaps or blindness later in life. In typical rod cone dystrophy (retinitis pigmentosa) there is relevant visual loss in the third decade with implications for the patients' professional life, their mobility and their private life. For this reason, the disease is relevant for the individual patient as well as for society in general. We investigated social issues in 233 retinitis pigmentosa patients: 9.9% are not able to read any more; 40.9% have never had a driver's license and 27.8% quit driving because of a visual handicap. The mean reduction in the capacity for work is 86%; 12.7% are unable to work and therefore receive public financial support; 22.6% are unable to work in their profession; 20.9% are receiving public support because of legal blindness. Against this background it seems to be important that ophthalmologists inform their patients thoroughly about the implications of the disease for their professional and private lives. Doing this, he/she should ask for support from social service professionals.

Activities of Daily Living↗
PubMed1994

Inhibitory action of haloperidol, spiperone and SCH23390 on calcium currents in rat retinal ganglion cells.

Patch-Clamp measurements in the whole-cell configuration were performed on isolated rat retinal ganglion cells to record voltage-activated calcium currents in the presence of dopamine antagonists. We report here that, in the absence of dopamine, application of the receptor antagonists haloperidol, spiperone and SCH23390 reduced calcium influx between 8% and 77%. The effect was fully reversible. After application of haloperidol and SCH23390, Ca2+ currents (ICa) recovered rapidly and completely within 30 s of washing. Current recovery after application of spiperone was completed only after 2 min of washing. I-V plots showed no change in the voltage-dependence of ICa during drug application. Also current kinetics remained unaffected by the dopamine antagonists.

Action Potentials↗
PubMed1994

Brightness matching and colour discrimination in young diabetics without retinopathy.

This study used the methods of the Farnsworth-Munsell 100-hue test (FM-100), heterochromatic brightness matching (HBM) and wavelength discrimination to test the sensitivity and colour vision of 20 juvenile diabetics with no (16) or very mild (4) retinopathy. Their results were compared to an age-matched control group. The FM-100 results showed a significant increase in error scores throughout the spectrum in comparison to the controls. This deterioration in colour vision was confirmed in the results for the wavelength discrimination task, tested between 440 and 640 nm, where the just noticeable difference in colour was, in general, larger for the diabetic group than the control group. Only at 460 nm were the results of the diabetics similar to those of the controls. The diabetic group were also less sensitive than the control group in the HBM task between 480 and 600 nm. The results show that a deficit in sensitivity and colour vision occurs in diabetics before the onset of a clinically visible retinopathy.

Adolescent↗
PubMed1994

6-Hydroxy dopamine does not affect lens-induced refractive errors but suppresses deprivation myopia.

Degradation of the retinal image by translucent occluders during postnatal development induces axial myopia in chickens, tree shrews and monkeys. Local visual deprivation produces myopia even in local regions of the eye and neither accommodation nor intact connection between the eye and the brain are necessary. Therefore, it is an important question whether a similar local-retinal pathway translating visual information into growth or stretch signals to the underlying sclera is acting to emmetropize the growing eye. It is not known until now whether occluder deprivation triggers similar eye growth (or scleral stretch) mechanisms that are also responsible for visual guidance of normal refractive development. We here report that, in chickens, 6-hydroxy dopamine suppresses deprivation-induced myopia but has no effect on the magnitude of changes in axial eye elongation that are induced by spectacle lenses. The result suggests that, in chickens with normal accommodation, two pharmacologically different feedback loops may be responsible for deprivation myopia and lens-induced refractive errors.

Animals↗
PubMed1994

In vitro identification of retinal ganglion cells in culture without the need of dye labeling.

We here describe a method for the identification of a distinct neuronal phenotype at all stages of development in culture without the need of any staining procedure. Based purely on a size criterion we can rapidly select vital retinal ganglion cells (RGCs) for further studies out of a mixed culture of rat retinal cells. In order to establish a size criterion for retinal cells of various age, RGCs were first labeled immunocytochemically with antibody against the ganglion cell-specific surface glycoprotein Thy-1. Soma diameters were then determined for labeled and unlabeled cells between embryonic day 16 (E16) and postnatal day 90 (P90). Unlabeled neurons of all ages had soma diameters between 3.6 microns and 12 microns (mean diameter: 6.3 microns). In contrast, soma diameters of RGCs ranged from 8.4 microns to 28 microns and the number of RGCs with large soma diameters increased with age. Thus, in a mixed retinal cell culture only RGCs are larger than 12 microns and can be selected solely based on their size. The validity of the size criterion during the whole period of retinal cell differentiation offers the possibility to study the development of cellular functions and ion channel properties in a distinct type of cell without the risk of artifacts introduced by staining.

Animals↗
PubMed1994

[Effect of diffractive multi-focal lenses on contrast vision, glare sensitivity and color vision].

BACKGROUND: Due to theoretical considerations an increase in the depth of field of the diffractive IOL may be combined with a reduction in contrast sensitivity, glare sensitivity and colour perception. PATIENTS AND METHODS: A comparative analysis of both eyes was performed in ten patients with a diffractive multifocal IOL (3M 815LE) in one eye and a monofocal IOL in the other eye. Contrast sensitivity was examined by computer generated sine wave gratings of 6 different spatial frequencies; visual acuity with glare and glare sensitivity were determined under 7 different levels of field luminance; colour vision was examined using the Farnsworth-Munsell-100-Hue-test. RESULTS: Contrast sensitivity of the diffractive lens was reduced for intermediate spatial frequencies, but not for low and high frequencies. Visual acuity with glare was only reduced at maximum field luminance; no differences were found in glare sensitivity and colour perception between monofocal and multifocal. CONCLUSION: Altogether, the diffractive lens did not show a dramatic reduction in the examined visual functions compared with the monofocal IOL.

Aged↗
PubMed1994

[Electroretinography study of unanesthetized young children].

BACKGROUND: The electroretinogram (ERG) ist an important examination method for the evaluation of retinal dysfunction in children. However it is often difficult and sometimes almost impossible to examine especially younger children with usual methods. Because of its risks, general anesthesia is rarely used. METHODS: ERG examinations were performed without general anesthesia or sedation with DTL (Dawson-Trick-Litzkow) electrodes. These are conjunctival electrodes made of thin microfibers. Several additional modifications of the standard examination technique were utilized, which enabled us to examine children of almost any age. 10 volunteers and 34 children between 6 month and 9 years of age were examined. RESULTS: 62 eyes of 34 children were evaluated. The diagnostic problem could be solved in three quarters of the patients with the ERG. CONCLUSION: With the DTL electrode and some methodical changes in the standard ERG technique it is possible to perform ERG's in little children without anesthesia or sedation. This method can be applied in children over 2 years of age. Below this age an sedation of any kind is necessary.

Child↗
PubMed1994

[Experimental studies of the significance of the renin-angiotensin system in the retina. A review].

BACKGROUND Many peptides now identified in the brain were previously thought of as exclusively peripheral hormones. Among those, the renin-angiotensin system (RAS) is not only found to be of great importance in peripheral vasomotor and electrolyte homeostasis but also acts as neurotransmitter or modulator in the central nervous system. Here we review a number of experiments performed by us pointing to a modulation effect of the RAS unrelated to its vasoactive mechanisms. The biochemical basis as well as the different methods employed will be described in detail. METHODS RAS enzyme activity within the different ocular structures were determined by means of fluorimetric measurements. Possible neurophysiological effects of the RAS on retinal function were established through electroretinographic in-vitro and in-vivo recordings. Immunocytochemical staining was employed to morphologically identify possible sites involved. RESULTS The performed fluorimetric measurements revealed highest Angiotensin-Converting Enzyme (ACE) activity within the neuroretina. Electroretinographic experiments have shown that variation in angiotensin-II activity is followed by reversible, dose-dependent effects on inner retinal signals. Clear evidence was found by immunohistochemistry that there is a discrete subpopulation of angiotensin-positive cells in the inner retina. CONCLUSIONS These findings demonstrate that the Renin-Angiotensin-System has neuronal sources and is physiologically active in the mammalian retina not purely related to vasoactive mechanisms. The RAS effector hormone angiotensin-II might therefore be a putative neurotransmitter in a subpopulation of retinal neurons. Reported side-effects of vasoactive substances, such as ACE-inhibitors on the visual function might be explained hereby.

Animals↗
PubMed1994

[Differential diagnosis of cone dystrophies].

Electrophysiological and psychophysical findings recorded in 70 patients with three hereditary diseases of the cone system,--blue cone monochromatism, cone-rod dystrophy and selective cone dystrophy--were compared. Blue cone monochromatism is distinguished from the other two diseases by a reduction of visual acuity since childhood, without progression and with a sex-linked mode of inheritance. In addition, nystagmus is generally observed only in the time shortly after birth and the green and red cones are found to be missing on spectral sensitivity measurements. Cone-rod dystrophy can be distinguished from the blue cone monochromatism by a reduction in visual acuity later in life with progression of the symptoms. Spectral sensitivity measurements reveal reduced function of all three cones in cone-rod dystrophy and a single cone mechanism in selective cone dystrophy. Moreover, in cone-rod dystrophy the ERG reveals a reduction in the amplitudes of the photopic system and often mild involvement of the scotopic part. Measurement of the spectral sensitivity and the ERG can thus help in the diagnosis of these three hereditary diseases.

Color Perception↗