Biomedical subjects

H Wilhelm

Publications and source records attributed to H Wilhelm.

At least 19 recordsLinked to original sources

PubMed2003

The break-up of heavy electrons at a quantum critical point.

The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on the heavy-electron material YbRh2Si2 found that near a field-induced QCP electrons move ever more slowly and scatter off one another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and scattering cross-section. But these studies could not shed light on whether these properties were an artefact of the applied field, or a more general feature of field-free QCPs. Here we report that, when germanium-doped YbRh2Si2 is tuned away from a chemically induced QCP by magnetic fields, there is a universal behaviour in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current-carrying motions of the electron fluid.

Journal Article↗

PubMed2002

Relation between perceived driving disability and scores of vision screening tests.

AIM: To determine the relation between perceived driving disability and vision screening tests. METHODS: 93 subjects, aged 50 years and over, with binocular visual acuity of at least 20/80. Perceived driving disability (PDD) was assessed by a questionnaire. Subtracting daytime from night-time driving question scores revealed PDD at night (PDDN), subtracting scores of questions for driving in familiar places from those in unfamiliar places revealed PDD at unfamiliar places (PDDU). RESULTS: PDD was strongly related to visual acuity, contrast sensitivity and useful field of view (UFOV). Specific relations existed between PDDN and Nyktotests and Mesotests and between PDDU and UFOV. These associations were enhanced in a subset of subjects with better visual acuities. CONCLUSIONS: Vision screening tests correlate well with perceived driving disabilities, especially when a subtraction method is used in the questionnaire to reveal condition dependent disabilities. Additional tests for visual acuity are useful, especially in subjects with better visual acuity.

Automobile Driving↗

PubMed2002

Stereotactic fractionated irradiation of optic nerve sheath meningioma: a new treatment alternative.

BACKGROUND: Primary optic nerve sheath meningioma (ONSM) is a rare but almost invariably blinding tumour when its natural history is observed in a "wait and see" strategy. Surgery has hitherto only been advocated in case of progressive disease involving intracranial structures, as it leads to iatrogenic blindness in the overwhelming majority of cases. Therefore, treatment options bearing lesser risk of functional deterioration are highly desirable, both in cases of intracranial involvement as well as during earlier phases of the disease which are currently generally left untreated. The authors report the outcome of the largest series of patients to date treated by stereotactic fractionated irradiation as a new treatment approach in ONSM at all stages. METHODS: 15 patients (16 nerves) underwent stereotactic fractionated conformal irradiation with a total dose of 54 Gy, using standard fractionation. Main outcome parameters included visual acuity and visual field, as well as three dimensional remission as documented by imaging. RESULTS: Tumour control was confirmed in all 15 patients undergoing stereotactic fractionated conformal irradiation (mean follow up 37 (range 12-71) months). No patient developed functional deterioration during or after treatment. Moreover, visual acuity improved by more than two lines in one patient and the visual field improved in six cases. Visual outcome in the other patients remained unchanged. There were no significant side effects of radiation therapy. CONCLUSION: These data provide convincing evidence that stereotactic fractionated conformal irradiation is an effective treatment option for primary ONSM with minimal treatment related morbidity. It should therefore be considered as therapeutic option both in early stage ONSM where surgery cannot be justified as well as in later stages, where surgery is so far considered the first line approach.

Adolescent↗

PubMed2002

[A severe traffic accident--250 years ago. Medical history presentation].

During a scientific examination in July 1999 both crypts below the St. Martin's Church in Grünstadt, Germany, were opened and 9 coffins from the county family of Leiningen examined. This paper is concentrating on one of these persons: Georg Hermann (1679-1751), count of Leiningen-Westerburg-Altleiningen, who gave during the 18. century the city its barock character. He was also responsible for the rebuilding of the church. His skeleton revealed interesting pathological changes. Few years before his death the count had the accident to get run over by a heavy wagon which crushed the distal part of his legs. The fractures healed, but gave him an ancylotic and shortened left leg, which must have caused him a lot of suffering in his last years.

Accidents, Traffic↗

PubMed2001

Daytime variations in central nervous system activation measured by a pupillographic sleepiness test.

Pupil size is regulated exclusively by the autonomic nervous system, and in darkness is proportional to the level of central sympathetic tone. Spontaneous pupillary movements, while at rest in darkness and quiet, were recorded for a period of 11 min, using infrared video pupillography. Thirteen young adults took part in a 30-h experiment lasting from 08.00 h to 14.00 h on the following day. Pupillographic testing and completion of a self-rated scale for the estimate of sleepiness were repeated every two hours. Pupillary unrest index (PUI), as a measure of pupil size instability associated with daytime sleepiness, showed the lowest values at 09.00 h, when pupil size was found to be maximal, and 23.00 h. During the course of the day, amplitude spectrum < or = 0.8 Hz and PUI showed increasing values during the afternoon hours, followed by a decrease during the evening. Daytime variations in the pupillary unrest index in healthy normal subjects were found to be positively correlated with the level of alertness. These findings are similar to the daytime variations found by the MSLT (multiple sleep latency test) in young adults.

Adult↗

PubMed2001

[Automated swinging flashlight test in patients with optic nerve diseases].

AIM OF THE STUDY: The swinging flashlight test is an objective method to diagnose a lesion of the anterior visual pathways. However, errors and faults may easily alter the test's results. Hence, the value of the swinging flashlight test depends highly on the examiner's skills. Therefore an automated and objective procedure was developed which is independent from the examiner. METHODS: A binocularly measuring instrument adapted for video pupillography was supplied with two arrays of light emitting diodes in front of each eye of the subject. By means of this illumination, pupillary light reflexes are elicited alternately. Pupil size is registered continuously, and after artifact elimination, the response amplitudes of the pupils are determined as a mean of right and left pupil. Responses elicited via right and left eye are compared. By varying the stimulus intensity it is possible to measure the amount of the relative afferent pupillary defect. The procedure was tested in 31 patients with optic nerve disorders. RESULTS: The measurements were easily feasible, stable and reliable. Correlation between the relative afferent pupillary defect detected manually by grey filter compensating and with the automated procedure proved to be high. Both variables correlated highly significant with a Spearman rank coefficient of 0.65. If the clinical test is regarded as the golden standard, the automated swinging flashlight test is able to detect 85% of the relative afferent pupillary defects > or = 0.3 logE and 94% of the defects > or = 0.6 logE. CONCLUSION: The automated swinging flashlight test can be recommended to exclude influences by the examiner or if the exact amount of the relative afferent pupillary defect is desired, e.g. when monitoring therapeutic effects in optic nerve diseases. Furthermore, an automated swinging flashlight test could serve as a screening test.

Adult↗

PubMed2001

[Optic neuritis as a complication in preventive tetanus-diphtheria-poliomyelitis vaccination: a case report].

BACKGROUND: The preventive value of vaccinations is generally accepted. Public recommended vaccinations are administered frequently and therefore even rare complications may occur. PATIENT: We report on a 56-year-old patient who suffered from an acute unilateral optic neuritis, following ten days after vaccination against diphtheria, tetanus and poliomyelitis. A complete remission occurred within six weeks after intravenous megadose prednisolone. CONCLUSIONS: Neurological and ophthalmological complications following vaccinations are rare, and in most cases reversible.

Diphtheria-Tetanus-Pertussis Vaccine↗

PubMed2000

Xkid, a chromokinesin required for chromosome alignment on the metaphase plate.

Metaphase chromosome alignment is a key step of animal cell mitosis. The molecular mechanism leading to this equatorial positioning is still not fully understood. Forces exerted at kinetochores and on chromosome arms drive chromosome movements that culminate in their alignment on the metaphase plate. In this paper, we show that Xkid, a kinesin-like protein localized on chromosome arms, plays an essential role in metaphase chromosome alignment and in its maintenance. We propose that Xkid is responsible for the polar ejection forces acting on chromosome arms. Our results show that these forces are essential to ensure that kinetochores and chromosome arms align on a narrow equatorial plate during metaphase, a prerequisite for proper chromosome segregation.

Amino Acid Sequence↗

PubMed2000

Microembolic signals and clinical outcome in patients with acute stroke--a prospective study.

The occurrence of microembolic signals (MES) in patients with transient ischemic attack (TIA) or stroke has already been described; the influence of the time interval between onset of symptoms and transcranial Doppler monitoring (TCD) on the MES rate or MES prevalence and the possible prognostic value of the early detected MES rate on the outcome of TIA or stroke symptoms in a 3 month interval are discussed. In a prospective study we evaluated 61 patients consecutively admitted to our stroke unit after their first ischemic neurological deficit involving the vascular territory of MCA and/or ACA. All of the patients underwent a 30-minute bilateral transcranial Doppler monitoring of their MCAs for the identification of MES. Monitoring was performed within 12.3 + -9.3 (average mean + -SD) hours of stroke onset for the first time, the second time 48 hours after first TCD monitoring. Prognosis for the recovery of neurological deficits was evaluated by using the Barthel index (BI) and Scandinavian Stroke Scale (SSS) at the time of admission of the patient to the stroke unit, and with Barthel indices after one month and after 3 months. As a result, 56% of all patients showed MES in at least one of the two registrations. MES were recorded not only on the symptomatic side. The MES prevalence between both TCD monitorings was significantly different (total MES prevalence: 1st TCD: 26 patients: 2nd TCD: 13 patients; p < 0.04; ipsilateral MES prevalence: 1st TCD: 19 patients; 2nd TCD: 9 patients; p < 0.01). The regression analysis showed a significant influence of the total MES rate on both neurological scores at admission (SSS: 0.03; Barthel index: 0.04), but not for the Barthel scores after one and three months. In conclusion, we found an influence of the time interval between onset of neurological symptoms of TIA or stroke on the MES rate and the prevalence of MES. The prevalence of MES or the MES rate, found after a short time interval to the onset of symptoms, did not have a prognostic value on the outcome of neurological deficits up to a three month follow-up.

Adult↗

PubMed2000

Naso-temporal asymmetry and contraction anisocoria in the pupillomotor system.

BACKGROUND: Differences between the pupillomotor sensitivity of nasal and temporal retinal hemifields may contribute to the relative afferent pupillary defect (RAPD) seen in optic tract or pretectal lesions. To understand the architecture of the pupillary pathway, it is necessary to know the size and the prevalence of such naso-temporal differences and also of contraction anisocoria (unequal direct and consensual pupillary responses) in normal individuals. The results of previous studies have been only partially consistent. METHODS: We registered the direct and consensual pupillary light reactions in both central retinal hemifields of 42 healthy subjects by means of IR video pupillography. Stimuli were generated under mesopic conditions on a computer screen as half-circles with 4.6 cd/m2 and 10 deg radius. Stimulus duration was 200 ms with a stimulation interval of 4 s. RESULTS: The nasal retina was significantly more sensitive than the temporal retina, and the direct pupillary reactions were significantly larger than the consensual reactions. For the nasal retina, direct pupillary reactions exceeded the consensual reactions, whereas there was nearly no difference between direct and consensual reactions for the temporal retina. CONCLUSION: RAPD in optic tract damage or pretectal lesions cannot be explained by the only slightly more sensitive nasal retina. Considerably more input would be needed from the contralateral than from the ipsilateral retina into the optic tract. The nearly equal direct and consensual pupil reactions when stimulating the temporal retina suggest an input of temporal retina to both sides of the pretectum. Such a crossing of temporal fibres may take place in the chiasm.

Adult↗

PubMed2000

[Effect of dorzolamide on accommodation and pupillary reaction?].

PURPOSE: To test the effect of dorzolamide on accommodation or pupillary function. MATERIALS AND METHODS: This double-blind study examined 35 young subjects with normal ophthalmological findings. Before and after the application of two drops dorzolamide in one eye and placebo in the other eye the subjects were examined by pupillography, infrared video-retinoscopy, and subjective near-point determination. RESULTS: None of the parameters concerning accommodation or pupillary function differed significantly before and after application of the eye drops. CONCLUSION: Dorzolamide has no short-term effect on accommodation or pupillary function.

Accommodation, Ocular↗

PubMed2000

[Perimetry findings and driving performance. "How much visual field" does a motorist need?].

OBJECTIVE: On 01-01-99 the new driving licence regulations came into force. Are the visual field criteria mentioned there sufficient for an adequate evaluation of driving fitness? METHODS: Typical (binocular) visual field defects were digitally superimposed onto photographs of traffic scenes to show the influence of such scotomata on visual perception. RESULTS: Exemplary cases clearly show that evaluation of visual field borders alone is not sufficient for evaluating driving fitness. They also prove that binocular scotomata affecting the (para-)central region of the visual field are of special importance to driving performance. The actual guidelines given by the traffic commission of the German Ophthalmological Society (DOG) and the legally defined limits will be critically discussed. CONCLUSION: From the ophthalmological point of view the actual visual field criteria of the new driving licence regulations do not seem to be sufficient for the evaluation of driving fitness: An additional consideration of (para-)central scotoma is mandatory. This publication provides recommendations for execution and interpretation of perimetric examinations for traffic ophthalmological purposes.

Automobile Driver Examination↗

PubMed2000

Spontaneous fluctuations in pupil size are not triggered by lens accommodation.

Fluctuations in pupil size and lens accommodation are measured concurrently under open loop conditions, constant illumination and far fixation. In 12/17 trials no correlation was measured between the fluctuations in pupil size and lens accommodation. For the remaining 5/17 trials no lag was observed between the changes in pupil size and lens accommodation indicating that this correlation does not arise as a consequence of a near response. These observations suggest that under conditions of constant illumination and far fixation, the supranuclear centers controlling the near response are not active.

Accommodation, Ocular↗

PubMed2000

[Carcinoma-associated retinopathy: a review with clinical examples].

Cancer-associated retinopathy (CAR) is a rare paraneoplastic syndrome. In this survey we report about two further patients with CAR, who were referred to the University Eye Hospital of Tuebingen within a few months. The most common primary tumor associated with CAR is small cell carcinoma of the lung. Case reports about rhabdomyosarcoma, carcinoma of the endometrium, prostate and mamma were also described. The exact pathogenesis of CAR is still unknown. Specific autoantibodies were found against the photoreceptor protein recovering (23-kd retinal CAR antigen). However, this reaction is not present in all patients, and probably other antigens are also involved. Most of the patients experience symptoms of CAR before the primary tumor is detected. Besides glare sensitivity and flashing lights, a rapidly progressive, often asymmetric visual loss may occur. Although paracentral and mid-peripheral scotomas can be found frequently, visual field defects are often quite heterogeneous. Typically, the responses in the electroretinogram (ERG) are markedly reduced, but normal ERGs were also described. The fundus picture in CAR shows sheathing of the retinal vessels, narrowing of the arterioles and clumbing of the retinal pigment epithelium. The prognosis is poor. Frequently there is progression to bilateral loss of vision within a few months. Treatment of the primary tumor does not seem to alter the ocular prognosis. Systemic corticosteroids may be helpful in some patients. Nevertheless, no proven therapeutic regimen is currently available.

Aged↗

PubMed2000

Laboratory, clinical, and kindergarten test of a new eccentric infrared photorefractor (PowerRefractor).

PURPOSE: Photorefraction is a convenient way to determine refractive state from a distance. It is, therefore, useful for measuring infants and noncooperative subjects. However, its reliability (or precision) and accuracy (or validity) has been questioned. In a study in subjects without cycloplegia, we have tested whether, after complete automatization, eccentric photorefraction at a 1-m distance can be as reliable as a common autorefractor. METHODS: In a laboratory study of 15 student subjects without the use of cycloplegia (30 eyes, refractive errors ranging from -6 D to +6 D), age 25 to 31 years, the photorefractive measurements were compared with spectacle prescriptions. In a clinical study, photorefraction, autorefraction, and subjective refraction were performed in 40 patients without cycloplegia (refractive errors ranging from -4 D to +4 D), most of them with various ocular pathologies. Subjective refractions were obtained by an experienced clinical ophthalmologist but were not accessible to the examiner who used the two refractors. Visual acuity was 20/20 or better except for five subjects. Ages ranged from 6 to 75 years. In the kindergarten screening study, 108 children aged 3 to 6 years were screened for refractive errors. RESULTS: In the laboratory study, it was found that the mean difference between spectacle prescription and PowerRefractor measurements was < 0.6 D for spheres and below 0.4 D for cylinders. In the clinical study, data were obtained by all three procedures in 78 eyes. The photorefractor and the autorefractor performed similarly for spheres (mean absolute dioptric difference between refractor and subjective measure: 0.593 D and 0.696 D) and cylinders (mean absolute dioptric differences: 0.399 D and 0.389 D). However, the photorefractor was superior with regard to the measurement of the magnitude and axis of astigmatism (mean weighted difference between objective and subjective axis 0.644 D and 0.769 D, respectively). In the kindergarten study, it was found that the PowerRefractor was very convenient to handle. The autorefractor measured more myopic refractions than the PowerRefractor (mean of the left eyes 0.11 +/- 1.1 D vs. 0.62 +/- 0.53 D, p < 0.001). There was no indication that the PowerRefractor failed to detect hyperopia, because all but one child with more than 2 D of hyperopia measured with autorefractor (n = 7) was also hyperopic with the PowerRefractor. Furthermore, presenting an interesting fixation target at a 3-m distance did not cause more hyperopic refractions, indicating that the camera of the PowerRefractor at a 1-m distance was not a significant stimulus to accommodation. CONCLUSIONS: The PowerRefractor was shown to have comparable or slightly better reliability and accuracy than a modern autorefractor; however, it has major advantages over current autorefractors in that it is faster, measures both eyes at once, and gives interpupillary distance, pupil size, and information on the alignment of the eyes at the same time.

Adolescent↗

PubMed2000

Pupil perimetry using M-sequence stimulation technique.

PURPOSE: M-sequence stimulation technique allows mapping of the retinal function by multifocal electroretinographic (ERG) recordings. However, the information provided about visual field is limited to retinal function. Optic nerve diseases and diseases of the higher visual pathways usually show normal multifocal ERGs. Using pupillary responses instead of the electrical retinal responses might enhance the diagnostic possibilities of this system. The problems of local ERG recordings are very similar to those encountered in pupil perimetry: Local stimuli have to be dim to avoid or at least reduce stray-light responses. Dim stimuli, close to the absolute threshold, elicit only subtle pupillomotor responses. Therefore, techniques that are able to detect small focal responses are promising. METHODS: Pupillography was done by means of an infrared video camera and real time image processing (50 Hz) using a custom-designed videoboard in a personal computer (486). Recording conditions: The stimulus was presented on a monitor (75 Hz) in 26 cm distance from the patient's eyes. It contained 37 hexagons in a 25 degrees visual field. Each element changed between black (1.6 cd/m2) and white (160 cd/m2) after a binary M-sequence independently from other elements. Four thousand ninety six different stimulus pictures of 120-msec duration were shown during a single pupillogram recording. Thirty-seven local pupillograms were calculated in a cross-correlation of stimulus sequence and the pupil diameter. RESULTS: The pupillomotor fields in normals showed a shape and sensitivity distribution as known from conventional pupil perimetry techniques. Artificial paracentral scotomas (5 degrees) created by masking different locations could be demonstrated convincingly. Even in patients with optic nerve lesions it was possible to demonstrate visual field defects. CONCLUSIONS: Pupil perimetry using the M-sequence technique is a promising method of objective perimetry that may find its entrance into clinical application.

Adult↗

PubMed1999

Pupillary light reflexes in patients with Leber's hereditary optic neuropathy.

BACKGROUND: According to a recent pupillographic study, patients with Leber's hereditary optic neuropathy (LHON) show the same pupillary behaviour as normals. Because this raises many questions concerning the real nature of LHON and challenges our concept of the afferent pupillary system, we tried to verify the results of this study. METHODS: Pupillary function was assessed in 34 normal subjects and 40 patients with LHON. Pupillary light reflexes were recorded by means of the Compact Integrated Pupillograph (CIP, AMTech). Under mesopic conditions 200-ms stimuli were presented at two different stimulus intensities. Latency, constriction amplitude and baseline diameter were defined automatically. Pupil light reflexes were compared between LHON patients and normals and between the better and the worse eye in 20 LHON patients with different visual acuities. RESULTS: For both stimuli there were significant differences in latency between LHON patients and controls. The latency of the pupil light reflex proved to be about 20 ms longer for LHON patients, and the amplitude was significantly smaller for the bright stimulus. Within LHON patients, the eyes with the worse visual acuity had a significantly smaller constriction amplitude than the eyes with the better visual acuity. CONCLUSION: The results of our study confirm that LHON really is an optic nerve disease and that the pupillary light reflexes are not normal.

Adult↗

PubMed1999

[Bilateral optic disk edema in polyneuropathy, organomegaly, endocrinopathy, monoclonal proteins and skin changes (POEMS syndrome)].

BACKGROUND: POEMS occurs only in about 1% of plasmocytoma cases, but in more than 50% of the rare osteosclerotic subtypes and plasma cell dyscrasias. The estimated frequency is 20 cases per year in Germany. Swelling of the optic disks is an early sign of the syndrome. CASE REPORT: An osteosclerotic plasmocytoma type IgA lambda was known in a 63-year-old farmer for 4 years. The primary lesion in the left femur was irradiated at diagnosis. Half a year prior to our examination the patient experienced edema of the legs and recurrent diarrhea. A staging confirmed the earlier diagnosis of a POEMS syndrome. The patient was presented for ophthalmologic examination because of optic disk swelling and progressive visual field defects: raster perimetry revealed enlarged blind spots and increased thresholds. Neurologic examination revealed polyradiculitis, increased protein levels in the cerebrospinal fluid and intracranial hypertension. The patient was treated with oral steroids which entailed improvement of the visual fields and decrease of optic disk swelling. CONCLUSIONS: Ophthalmologists play an active role in the staging, in the ruling out of other causes, and in the treatment. Symptomatic treatment with oral steroids should be monitored with visual acuity, raster perimetry and fundus examinations.

Diagnosis, Differential↗