PubMed Health⌕ Search

Biomedical subjects

M Fronius

Publications and source records attributed to M Fronius.

At least 19 recordsLinked to original sources
PubMed2006

[Visual distortions and depersonalization-de-realization syndrome].

Disturbances of visual perception like micropsia, macropsia, teleopsia, pelopsia, metamorphopsia or loss of stereoscopic depth perception are usually considered in ophthalmology as symptoms of retinopathy, especially maculopathy or disorders of binocularity. Differential diagnostic considerations include disorders like migraine and epilepsy but not the visual disturbance pertaining to the depersonalization-de-realization syndrome, although the above-mentioned symptoms are more prevalent in this psychogenic disorder. This article gives a review of depersonalization-de-realization in order to enable the ophthalmologist to include this syndrome into his diagnostic considerations.

Depersonalization↗
PubMed2006

[Adaptation of visual distortions in children with strabismic amblyopia following strabismus surgery and occlusion therapy].

BACKGROUND: Reduced visual acuity and deficient binocularity are well-known symptoms of amblyopia. Distortions of visual space perception were reported more recently in strabismic amblyopia. This study investigated whether strabismus surgery and occlusion therapy have an influence on these deficits in amblyopic children. MATERIALS AND METHODS: Two aspects of vertical alignment of amblyopic eyes, namely spatial distortion and spatial uncertainty, were investigated prospectively in 13 children (mean age 6 years 9 months) before and after strabismus surgery and in 12 children (mean age 6 years 11 months) during 6 months of occlusion therapy. RESULTS: A different impact of the two types of therapeutic intervention was observed: a slight (statistically not significant) increase of uncertainty was the only change noticed postoperatively after 1 week, spatial distortions were not affected. During occlusion treatment, both clear shifts of alignment and a decrease of uncertainty occurred. CONCLUSIONS: The geometry of visual space of amblyopic children showed modifications due to altered visual experience during treatment, most obviously during occlusion therapy. These changes are evidence for unknown features of plasticity of the amblyopic visual system initiated by treatment.

Amblyopia↗
PubMed2005

Transport of sodium and chloride across earthworm skin in vitro.

We present a new invertebrate model for the study of epithelial sodium transport in tight epithelia, the earthworm integument. Dissected segments of earthworm integument were mounted in modified Ussing chambers and perfused with either pond water (PW) or earthworm ringer solution (ERS) on the apical side. In order to investigate ion transport under near-in vivo physiological conditions, measurements were performed under current-clamp conditions by monitoring the transepithelial potential (V (T)), as well as the transepithelial resistance (R (T)). These were recorded continuously and the virtual short circuit current (I (SC)) was calculated. The integument has a high transepithelial resistance (R (T) = 9,037 +/- 502 Omega cm(2) for PW, n = 24, and 11,055 +/- 1,320 Omega cm(2) for ERS, n = 32). V (T) was -3.7 +/- 2.2 mV for PW (n = 24) and -1.5 +/- 1.0 mV for ERS (n = 32), and I (SC) was -0.57 +/- 0.30 microA/cm(2) for PW (n = 24) and -0.44 +/- 0.24 microA/cm(2) for ERS (n = 32). Only under PW, but not under ERS conditions, was there a pronounced inhibition of I (SC) by low doses of amiloride or its analogues phenamil and benzamil. The resistance of the paracellular pathway was found to be very high. The terrestrial oligochaete Lumbricus seems especially adapted to the environmental conditions because it has an ultra-tight integument and a very fast up- and down-regulation of apical Na(+) channels.

Animals↗
PubMed2003

Prostaglandin E2 induces upregulation of Na+ transport across Xenopus lung epithelium.

The apical mucus on pulmonary epithelia is not only critical for physiological functions such as gas exchange or inflammatory processes, but also contains surfactants and multiple molecules that mediate cellular responses. A tight control of transepithelial ion transport maintains viscosity of this layer and, e.g., the amiloride-sensitive sodium channels (ENaCs) in lung epithelia of vertebrates are the most important regulatory sites for transcellular sodium uptake. Dysfunction of this sodium transport results in reduced liquid absorption and causes massive problems with gas exchange. We used dissected lungs of Xenopus laevis in Ussing chambers to investigate the influence of prostaglandin E2 (PGE2) on the regulation of short-circuit current (ISC) and amiloride-sensitive sodium absorption (Iami). Apical application of PGE2 (1 microM) increased ISC by 38% and Iami by approximately 60%. In contrast, a different prostaglandin, PGI2, neither affected ISC nor Iami. Forskolin increased current to a similar magnitude and preincubation of the lung with an RP-isomer of cyclic AMP, an inhibitor of protein kinase A (PKA), abolished the effects of both PGE2 and forskolin. Transepithelial Na+ uptake was also upregulated by the prostaglandin receptor agonists misoprostol and sulprostone. The Iami in Xenopus oocytes that heterologously expressed ENaCs was not affected by PGE2.

Animals↗
PubMed2003

Stimulation of transepithelial Na(+) current by extracellular Gd(3+) in Xenopus laevis alveolar epithelium.

In the present study we investigated the effect of extracellular gadolinium on amiloride-sensitive Na(+) current across Xenopus alveolar epithelium by Ussing chamber experiments and studied its direct effect on epithelial Na(+) channels with the patch-clamp method. As observed in various epithelia, the short-circuit current ( I(sc)) and the amiloride-sensitive Na(+) current ( I(ami)) across Xenopus alveolar epithelium was downregulated by high apical Na(+) concentrations. Apical application of gadolinium (Gd(3+)) increased I(sc) in a dose-dependent manner ( EC(50) = 23.5 microM). The effect of Gd(3+) was sensitive to amiloride, which indicated the amiloride-sensitive transcellular Na(+) transport to be upregulated. Benz-imidazolyl-guanidin (BIG) and p-hydroxy-mercuribenzonic-acid (PHMB) probably release apical Na(+) channels from Na(+)-dependent autoregulating mechanisms. BIG did not stimulate transepithelial Na(+) currents across Xenopus lung epithelium but, interestingly, it prevented the stimulating effect of Gd(3+) on transepithelial Na(+) transport. PHMB increased I(sc) and this stimulation was similar to the effect of Gd(3+). Co-application of PHMB and Gd(3+) had no additive effects on I(sc). In cell-attached patches on Xenopus oocytes extracellular Gd(3+) increased the open probability ( NP(o)) of Xenopus epithelial sodium channels (ENaC) from 0.72 to 1.79 and decreased the single-channel conductance from 5.5 to 4.6 pS. Our data indicate that Xenopus alveolar epithelium exhibits Na(+)-dependent non-hormonal control of transepithelial Na(+) transport and that the earth metal gadolinium interferes with these mechanisms. The patch-clamp experiments indicate that Gd(3+) directly modulates the activity of ENaCs.

Animals↗
PubMed2002

[Some aspects of the current controversy about the treatment of amblyopia].

Occlusion has been used for centuries for treating amblyopia but in recent years an intensive debate about the treatment has arisen. The aim of this article is to summarize some of the new aspects of this discussion: on the one hand the effect of occlusion treatment during childhood is being questioned and on the other hand experimental approaches are being tested which are aimed at treating amblyopia in adults. Evidence from own experimental work is presented showing the influence of occlusion on the spatial localization of visual stimuli. A continuation of research on amblyopia and the effect of the therapy is urgently needed.

Adolescent↗
PubMed2001

Inhibitory non-genomic effects of progesterone on Na+ absorption in epithelial cells from Xenopus kidney (A6).

The effect of the steroid hormone progesterone on transepithelial sodium transport was measured in confluent monolayers of the A6-cell line from Xenopus kidney. Apical permeabilization with Amphotericin B enabled us to measure the Na+/K+-pump current, and current-fluctuation analysis was used to analyze changes in apical channel density and gating characteristics. Basolateral progesterone (22.2 microM) had a rapid inhibitory effect on the Na+/K+-pump current, and a corresponding decrease in Na+ channel density. The effect occurred within some minutes and took about 50 min to reach a new steady state, in which 45% of the macroscopic current (ISC) was inhibited. Progesterone also inhibits the hypo-osmotic stimulation of Na+ channels which occurs in untreated monolayers. Compared with the known effects of adrenal steroids, our results show a rapid inhibitory action of a steroid hormone on Na+ absorption. The time profile of the progesterone effect suggests, at least in the first minutes, a non-genomic action of progesterone.

Amiloride↗
PubMed2000

[Contrast media-enhanced 3D MR angiography before endovascular treatment of aneurysm in the abdominal aorta, iliac artery and peripheral vessels].

PURPOSE: The value of DSA for the measurement of aortic and peripheral arterial aneurysm dimensions before endovascular treatment is limited by projection effects. It was evaluated if additional gadolinium-enhanced three-dimensional MR angiography (3D-CEMRA) could compensate for the disadvantages of DSA. MATERIALS AND METHODS: 21 patients with 35 aneurysms in the abdominal aorta (14), iliac (9) and femoropopliteal vessels (12) were assessed with DSA (7 with calibrated catheter, 14 with yardstick) and 3D-CEMRA (TR/TE 7.8/2.1 ms, flip-angle 40 degrees, Matrix 512 x 224, FOV 500 mm, eff. slice 1.8 mm). We measured and compared aneurysm dimensions on both modalities. 3D-CEMRA was regarded as the reference method to evaluate the dimension of DSA-projection effects. RESULTS: Diameter and length of aneurysms were underestimated on DSA with the yardstick as reference. The deviation ranged from 15% (+/- 5%) in the aorta to 21% (+/- 10%) in the iliac vessels. Only with calibrated catheters as reference (7/21 DSA), were the distances on DSA correlated well with MRA. In 2/35 aneurysms 3D-CEMRA detected thrombosis with difference between length of inner lumen dilatation on DSA and whole aneurysm length. 2/5 accessory renal arteries found on DSA were not detected on 3D-CEMRA. CONCLUSIONS: 3D-CEMRA is a valuable adjunct to DSA for pre-interventional diagnostics of aortic and peripheral arterial aneurysms. It provides exact evaluation of aneurysm dimensions and information about partial thrombosis.

Aneurysm↗
PubMed2000

Preliminary report: monocular spatial localization in children with strabismic amblyopia.

Defective spatial localization is an important feature of strabismic amblyopia. Based on our experience from testing adult strabismics under various test conditions, we developed a test for assessing vertical alignment in strabismic children. Patients had to align a vertical test line with the apices of two vertically arranged reference triangles, under the control of both the dominant eye and the amblyopic eye. Means and standard deviations of several judgements represent systematic errors and uncertainty of alignment. We tested 27 strabismic and 34 age-matched control children aged 4.5-10 years. Control children showed a scatter of mean systematic alignment around the correct position of up to 7 minarc. In the amblyopic eyes of strabismic children, uncertainty was consistently higher than in the eyes of the control children. Systematic errors outside the normal range frequently occurred. In children tested repeatedly during occlusion therapy, uncertainty decreased as visual acuity improved. In several cases we observed changes of systematic vertical alignment during therapy, sometimes unexpectedly in the sense of a change in the direction of mislocalization or an initial increase and later decrease of errors. Thus, children with strabismic amblyopia show spatial localization deficits which are similar to those of adult strabismic amblyopes. Both spatial uncertainty and systematic distortions are susceptible to change due to enforced use of the amblyopic eye during occlusion therapy.

Amblyopia↗
PubMed1994

Pointing errors in strabismics: complex patterns of distorted visuomotor coordination.

Monocular eye-hand coordination was tested in a pointing experiment in the central and peripheral visual field of each eye of strabismic and anisometropic amblyopes, strabismic alternators and normal controls. In the normal controls, pointing was accurate in the central visual field. Towards the periphery, normal observers showed a varying amount of undershoot as well as increasing uncertainty. The pointing pattern was similar in the two eyes of these subjects. Increased uncertainty of pointing responses was found in most amblyopic eyes as compared to the dominant eyes. Three strabismic amblyopes and one strabismic alternator also had systematic pointing errors (i.e. systematic differences between pointing under the control of the dominant as compared to the nondominant eye). The pointing pattern was not uniform across the visual field in some of the strabismics, but was composed of areas of larger and smaller pointing errors. Larger pointing errors (i.e. larger differences between the dominant and nondominant eyes) were usually found in the central visual field. These errors were not closely related to the angle of squint. The clinical history of the strabismics seems to be an important factor for the occurrence of pointing errors.

Adolescent↗
PubMed1994

The development of visual acuity in the peripheral visual field of human infants: binocular and monocular measurements.

We measured binocular and monocular grating acuity in the peripheral visual field of infants, using a modified preferential looking procedure. Both binocular and monocular peripheral acuity increased between 2 and 11 months of age, but had not reached adult levels at the end of the first year of life. Binocular acuity was always higher than monocular acuity. At all ages tested, acuity was higher in the temporal than in the nasal visual field. We conclude that, in spite of the relative morphological maturity of the peripheral retina, visual acuity develops in the peripheral visual field.

Adult↗
PubMed1992

[Localization disorders in squint amblyopia: horizontal line bisection and relative vertical localization].

We used two different procedures for the evaluation of spatial localization errors in strabismic and anisometropic amblyopes, strabismic alternators and normal control subjects: partitioning of horizontal lines and vertical alignment. We found defective spatial localization in the amblyopic eyes of squinters with both procedures. However, in the horizontal partitioning experiment, the control subjects also showed asymmetries between the two hemifields. Thus, there is no good baseline under these conditions for the results of the amblyopic eyes of squinters. Our results show that vertical alignment is the more appropriate procedure to quantify defective spatial localization in strabismic amblyopes.

Discrimination Learning↗
PubMed1990

Human amblyopia: structure of the visual field.

Kittens raised with different kinds of abnormal early visual experience (monocular and binocular deprivation, convergent strabismus, eye rotation, asymmetric alternating occlusion, early callosal split) show systematic deficits in the nasal visual field of the affected eye. To test whether abnormal visual experience produces similar deficits in the human visual system, we measured the monocular visual field of humans with subnormal binocular vision (strabismic and anisometropic amblyopes, strabismics with alternating fixation). Eight amblyopes were tested with a computer-assisted static perimetry (Octopus 2000). Twenty other subjects were tested with kinetic perimetry (Goldmann 940), 11 subjects with static perimetry (Goldmann 940). In some of these subjects, we measured the latency of saccades and the accuracy of visually guided pointing toward stimuli presented in the peripheral visual field. Both strabismic and anisometropic amblyopes frequently showed deficits of visual sensitivity in the central part of the visual field, but no systematic deficits in the peripheral field of the amblyopic eyes. Strabismic alternators had practically equal fields in the two eyes. Neither saccadic latency nor pointing accuracy showed a systematic impairment in the nasal visual field. The discrepancy between the field losses in strabismic humans and in cats raised with a surgically induced squint cannot be due to methodological differences, but rather to anatomical differences, or to the different origin of strabismus in the two species.

Adult↗
PubMed1990

A perspective on psychophysical testing in children.

In this paper, we show that the development of acuity in infancy is not due solely to foveal maturation, since there is a clear development of acuity in the peripheral visual field. The development of peripheral acuity, and the naso-temporal asymmetry during early development reinforce the idea that the visual loss in adult strabismic amblyopes is not due to an arrest of development, but rather to the chronic interocular suppression of the deviated eye. The Teller Acuity Card Test does not reliably detect strabismic amblyopia, and therefore should not be recommended as a screening test. However, the test is adequate for diagnosing visual losses in children with organic eye disorders and possibly anisometropia.

Adolescent↗
PubMed1989

[Visual field defects in strabismic amblyopes].

Kittens raised with different kinds of abnormal early visual experience (monocular and binocular deprivation, convergent strabismus, eye rotation, asymmetric alternating occlusion, early callosal split) show systematic deficits in the nasal field of the affected eye. Since the kittens' visual field is tested by monitoring their orienting toward visual stimuli, it is not clear whether these deficits are due to a genuine sensory loss (involving the geniculocortical pathway) or to a sensory-motor impairment (involving the projection through the visual cortex to the superior colliculus). To answer this question, the authors measured the monocular visual field of humans with subnormal binocular vision (strabismic and anisometropic amblyopes, strabismics with alternating fixation). Eight amblyopes were tested with a computerized static perimetry (Octopus 2000). Twenty other subjects were tested with static and kinetic perimetry (Goldmann 940). In some of these subjects, we also tested the latency of saccades and the accuracy of visually guided pointing toward stimuli presented in the nasal or the temporal visual field. Both strabismic and anisometropic amblyopes occasionally showed deficits of visual sensitivity in the central part of the visual field, but no systematic deficits in the peripheral visual field. Strabismic alternators had practically equal fields in the two eyes. Neither saccadic latency nor pointing accuracy showed any asymmetries between the nasal and temporal visual fields. These results seem to contradict a recent report of a nasal hemianopia in deep amblyopia (Mehdorn, 1986); taken together, these results suggest that in adult strabismic humans, a nasal field loss is the exception rather than the rule.(ABSTRACT TRUNCATED AT 250 WORDS)

Amblyopia↗
PubMed1989

Different patterns of retinal correspondence in the central and peripheral visual field of strabismics.

We tested the state of retinal correspondence at different positions in the visual field of ten observers with strabismic and/or anisometropic amblyopia, four strabismic subjects with alternating fixation and three normal controls. Correspondence was evaluated by the subjective displacement of dichoptic stimuli; to estimate the displacement, we used red-green filters, Bagolini striated glasses, polarizing filters and a phase-difference haploscope. Strabismic observers (amblyopes and alternators) frequently showed variations in the angle of anomaly (ie, the amount of shift of space coordinates in the squinting eye) between different regions of the visual field. Correspondence tended to be closer to normal in the central field and more anomalous in the periphery. These findings cannot be explained by the progressive loss of localization sensitivity with increasing eccentricity. We suggest that the different patterns of retinal correspondence in the central and peripheral visual field of some strabismic observers might be due to a mechanism of selective stabilization of binocular connections in the peripheral visual field, where the larger corresponding areas overcome a limited misalignment of the eyes. In the central visual field, normal correspondence is preserved, and diplopia has to be prevented by interocular suppression.

Adolescent↗
PubMed1989

Monocular geometry is selectively distorted in the central visual field of strabismic amblyopes.

Strabismic amblyopia is associated with a distorted perception of visual space. The aim of our study was to investigate the monocular space perception of strabismic observers at several locations in the central and peripheral visual field. We tested nine observers with strabismic and/or anisometropic amblyopia, two strabismic subjects with alternating fixation and two normal control subjects. The task was to align a light stimulus with two vertically arranged reference marks. Testing conditions included three separations of the references along the vertical meridian (10 degrees, 20 degrees and 40 degrees) as well as several presentation sites of the vertical references in the nasal and temporal peripheral visual field (5 degrees, 10 degrees and 20 degrees from fixation). Performance with the amblyopic eye was clearly impaired as compared to the nonamblyopic eye. For alignment along the vertical meridian, all amblyopic eyes showed increased uncertainty in their position judgements. Most of the squinting eyes of amblyopes also displayed a systematic lateral displacement of the test stimulus in relation to the reference marks, in the most extreme case up to almost 7 degrees. Usually, larger errors were found with wider separations of the reference marks. In the peripheral field, the differences between the amblyopic and the nonamblyopic eye diminished or disappeared. Thus, monocular geometry appears to be selectively impaired in the central visual field of the deviated eye of strabismic amblyopes. These spatial distortions might be related to the different states of binocular correspondence in the central vs. peripheral visual field, shown by some strabismic amblyopes.

Amblyopia↗