Biomedical subjects

G Schwerdtfeger

Publications and source records attributed to G Schwerdtfeger.

4 recordsLinked to original sources

PubMed2006

[Bitemporal hemianopia in road traffic].

BACKGROUND: Patients suffering from pituitary adenomas and diseases of the chiasma typically show a bitemporal hemianopia. The residual undisturbed nasal visual fields of both eyes should have an extension of (at least) 120 degrees and are according to the actual German traffic rules (FeVAndV) for cars of the classes A, B, M, L and T. The intact half fields fit geometrically to one virtual normal field, that seems to correspond in the centre of a normal field. Reports on this problem often do not address correctly the questions of suitability for participation in road traffic. PATIENTS: The case of a patient with typical bitemporal hemianopia illustrates the sensorial peculiarities: the functioning temporal retinal halves do not correspond. This patient suffered additionally from disturbing diplopia due to a small-angle exotropia. The extent of the performed eye muscle surgery was selected to induce a slight overcorrection, i. e., resulting in 3 to 5 degrees esotropia. This eliminated the diplopia, but resulted in a vertical scotoma of the extension of the esotropia. CONCLUSIONS: In bitemporal hemianopia the undisturbed nasal visual half fields do not add up to a "nearly normal field of one eye". Moreover, either diplopia or--much more dangerous in traffic--a central vertical scotoma is the result. The explanation for this is a sliding of the hemifields of each eye without stabilisation by corresponding areas of the retinas of the right and left eyes. The peripheral extension of the visual field is not the key to the problem to imagine how a patient with typical bitemporal hemianopia will visualise daily life and traffic. In bitemporal hemianopia there is substantially no eligibility for driving a car or motor bicycle in road traffic.

Adult↗

PubMed2005

Function and coding in the blowfly H1 neuron during naturalistic optic flow.

Naturalistic stimuli, reconstructed from measured eye movements of flying blowflies, were replayed on a panoramic stimulus device. The directional movement-sensitive H1 neuron was recorded from blowflies watching these stimuli. The response of the H1 neuron is dominated by the response to fast saccadic turns into one direction. The response between saccades is mostly inhibited by the front-to-back optic flow caused by the forward translation during flight. To unravel the functional significance of the H1 neuron, we replayed, in addition to the original behaviorally generated stimulus, two targeted stimulus modifications: (1) a stimulus in which flow resulting from translation was removed (this stimulus produced strong intersaccadic responses); and (2) a stimulus in which the saccades were removed by assuming that the head follows the smooth flight trajectory (this stimulus produced alternating zero or nearly saturating spike rates). The responses to the two modified stimuli are strongly different from the response to the original stimulus, showing the importance of translation and saccades for the H1 response to natural optic flow. The response to the original stimulus thus suggests a double function for the H1 neuron, assisting two major classes of movement-sensitive output neurons targeted by H1. First, its strong response to saccades may function as a saccadic suppressor (via one of its target neurons) for cells involved in figure-ground discrimination. Second, its intersaccadic response may increase the signal-to-noise ratio (SNR) of wide-field neurons involved in detecting translational optic flow between saccades, in particular when flying speeds are low or when object distances are large.

Action Potentials↗

PubMed2001

Characterisation of a concentrative type of adenosine transporter from Arabidopsis thaliana (ENT1,At).

Here we report on the isolation of an Arabidopsis thaliana cDNA that is able to complement a Saccharomyces cerevisiae mutant unable to synthesise adenine. This cDNA encodes a highly hydrophobic protein (ENT1,At) of 428 amino acids, showing high similarity to the human nucleoside transporter hENT1. Yeast cells expressing ENT1,At are able to grow on adenosine-containing media, adenosine import exhibited an apparent affinity (K(M)) of 3.6 microM, and led to accumulation of this nucleoside within the yeast cell. Transport is inhibited by various nucleosides. Typical inhibitors of ENT-type nucleoside transporters do not inhibit (3)H-adenosine import. The presence of protonophores abolished adenosine import, indicating that ENT1,At catalyse a proton-dependent adenosine transport. This is the first functional characterisation of a plant nucleoside transport protein.

Adenosine↗

PubMed1996

[Binocular problems caused by aniseikonia and anisophoria after cataract operation].

BACKGROUND: Cataract and refractive surgery aiming at emmetropia, runs the risk to induce binocular problems, e.g. asthenopia or diplopia. If the compatibility concerning binocularity is solely estimated by the calculation of the difference of the retinal image sizes, using intraocular lens formulas or so-called "aniseikonia-programs", important physiological facts are not considered. The actual amount of the aniseikonia, this is the difference of the image size which the patient perceives subjectively, depends on 3 parameters: 1. the optically induced difference of the retinal image size, 2. the spatial density of the retinal photoreceptors and the size of the receptive fields, 3. a possibly existing anomalous retinal correspondence for different retinal image sizes. Besides aniseikonia, the induction of postoperative anisophoria by the required spectacle correction is a considerable aspect. Aniseikonia and anisophoria can cause fusional problems or diplopia because of the mentioned parameters and/or disparity of the retinal images. CASE REPORT: Cataract surgery should reduce a monolateral high myopia, aiming emmetropia, in axial anisometropia. This resulted in one exemplary case in high aniseikonia with complaints, while in other, comparable patients only a small amount of aniseikonia could be measured by haploscopy. This preoperative refractive situation is comparable to refractive surgery. In a second case with symmetrical myopia of -4 D, binocular problems with diplopia and asthenopia were induced after monolateral cataract surgery by the combination of a moderate aniseikonia and anisophoria. CONCLUSIONS: To predict the actual postoperative aniseikonia it is necessary for the patient to wear a contact lens preoperatively for a short time to measure the aniseikonia by haploscopy, particularly prior to refractive surgery in axial length ametropia. Due to the different sizes of the receptive fields of the retina, different postoperative aniseikonias may result in spite of similar axial length anisometropia. The individual tolerance of an adult for a postoperatively created anisophoria is hardly predictable. It is obvious that the fusional stress ensued from aniseikonia and anisophoria adds or multiplies. In contrast to horizontal eye movements, vertical eye movements can hardly be compensated by head movements, as the use of bi- or multifocals requires a down gaze of about 30 degrees. Here a height-balance-prism could help.

Adult↗