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Biomedical subjects

H R Koch

Publications and source records attributed to H R Koch.

At least 19 recordsLinked to original sources
PubMed2006

Precision measurement of the quasifree pn-->dvarphi reaction close to threshold.

The quasifree pn-->dvarphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the K+K- decay of the varphi meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with s-wave production, the kaon angular distributions show the presence of p waves at quite a low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the eta meson.

Journal Article↗
PubMed2006

Near-threshold production of phi mesons in pp collisions.

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

Journal Article↗
PubMed2006

Evidence for an excited hyperon state in pp --> pK+Y0*.

Indications for the production of a neutral excited hyperon in the reaction pp --> pK+Y0* are observed in an experiment performed with the ANKE spectrometer at COSY-Jülich at p(beam) = 3.65 GeV/c. Two final states were investigated simultaneously, viz. Y0* --> pi+X- and pi-X+, and consistent results were obtained in spite of the quite different experimental conditions. The parameters of the hyperon state are M(Y0*) = (1480 +/-15) MeV/c2 and gamma(Y0*) = (60 +/- 15) MeV/c2. The production cross section for Y0* decaying through these channels is of the order of few hundred nanobarns. Since the isospin of the Y0* has not been determined here, it could either be an observation of the sigma(1480), a one-star resonance of the Particle Data Group tables, or, alternatively, a lambda hyperon. Relativistic quark models for the baryon spectrum do not predict any excited hyperon in this mass range and so the Y0* may be of exotic nature.

Journal Article↗
PubMed2003

a+0 (980)-resonance production in pp-->dK+K-0 reactions close to threshold.

The reaction pp-->dK+K(-)0 has been investigated at an excess energy of Q=46 MeV above the K+K(-)0 threshold with ANKE at the cooler synchrotron COSY-Jülich. From the detected coincident dK(+) pairs, about 1000 events with a missing K(-)0 were identified, corresponding to a total cross section of sigma(pp-->dK+K(-)0)=[38+/-2(stat)+/-14(syst)] nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p wave between the deuteron and the kaon system. This is interpreted in terms of a(+)0 (980)-resonance production.

Journal Article↗
PubMed2001

Low-dose-rate ionizing irradiation for inhibition of secondary cataract formation.

INTRODUCTION: Secondary cataract formation limits visual function after cataract surgery. Various experimental methods utilizing the pharmacologic inhibition of lens epithelial cell proliferation have been proposed. However, diffusion into the anterior chamber may lead to damage of corneal endothelial cells. This study evaluated the inhibition of lens epithelial cell proliferation with a capsular bag ring, labeled with a beta-emitting radioisotope. METHODS AND MATERIALS: In vitro studies using rabbit lens epithelial cells were performed to investigate the dose-dependent effect of irradiation. Based on these results, P-32-labeled PMMA rings were implanted into the capsular bag of NZW rabbits in vivo after phacoemulsification. Animals were examined for development of posterior capsule opacification over a period of 12 weeks following surgery. Radiation damage to the surrounding ocular tissue was subsequently analyzed in histologic sections using TUNEL assay and proliferation marker. RESULTS: Irradiation of lens epithelial cells in vitro with >5 Gy resulted in a dose-dependent decrease in the number of cells. BrdU testing demonstrated a near complete inhibition of cell proliferation. In vivo, implantation of P-32-labeled PMMA rings led to inhibition of epithelial cell proliferation and secondary cataract formation but was not able to fully inhibit aberrant differentiation of some remaining cells. Histologic examination showed no evidence of radiation damage of the ciliary body or the corneal endothelium. CONCLUSIONS: Low-dose beta irradiation exhibits the potential for inhibition of lens epithelial cell proliferation both in vitro and in vivo. Further investigation of various nuclides and their radiation profiles is needed to optimize the prevention of posterior capsule opacification due to epithelial cell proliferation.

Animals↗
PubMed1996

Lens bisector for silicone intraocular lens removal.

The lens bisector, designed to cut silicone intraocular lenses (IOLs) in the middle so they can be extracted through a 3.0 mm incision, consists of a disposable wire sling that can be pulled into a metal tube. After the IOL is moved into the anterior chamber, the sling is placed over its center and pulled completely into the tube, bisecting the lens atraumatically. The IOL halves are then extracted. A new IOL can be inserted through the same incision.

Humans↗
PubMed1994

Polishing methods for the lens capsule: histology and scanning electron microscopy.

Capsule opacification occurs when lens epithelial cells remains on the capsule after extracapsular cataract surgery. The cells divide and form fibers. The best way to prevent opacification is to remove all epithelial cells from the capsule. Our study compared the efficacy of different mechanical polishing methods in eyes in which cataracts were removed by endocapsular phacoemulsification through a miniature capsulorhexis. The capsular bag was polished using one of five techniques: metallic scrapers, silicone scrapers, Rentsch capsule curettes, irrigation/aspiration tip, or ultrasound irrigation/aspiration tip. Then a circular central portion of the anterior capsule was removed and processed for histology and scanning electron microscopy. A control group comprised unpolished central anterior capsules obtained by capsulorhexis before or after endophacoemulsification. The cleanest capsules were obtained by polishing with the ultrasound irrigation/aspiration tip.

Aged↗
PubMed1992

[Further development of a streak retinoscope with calibrated collimator].

Development and rationale of a new streak retinoscope have been discussed in an earlier paper. In contrast to classical retinoscopy this retinoscope determines the refraction by forming the narrowest streak in the test person's pupil with a calibrated collimator. In addition to the first prototype the extension of the lamp according to variation of the refraction is measured electronically and the data are transposed into a computer. This allows to freely choose a working distance in a range from about 30 to 120 cm and therefore it is possible to examine restless patients. Accuracy of the measurement was less than or equal to 0.25 D for Ametropia from -0.5 to 5.0 D in a working distance of 30 cm or from -4.0 to -1.5 D in 100 cm. In most persons it is not necessary to use additional glasses during refraction by choosing the adequate distance. Therefore this method can help to refract kids and other persons which could not be refracted by use of glasses. In addition this method excludes the accommodation of the patient as apposed to regular refractometers.

Calibration↗
PubMed1991

[Effects of acetazolamide (Diamox, Glaupax) on tear production].

In view of personal clinical observations, it appeared possible that a therapy with the carboanhydrase inhibitor acetazolamide leads to a reduction of tear production and induces a dry eye syndrome. Tear secretion was therefore measured by Schirmer tests in a control group of 66 patients after cataract surgery and in a test group of 20 patients who were treated with acetazolamide (Diamox, Glaupax) on the day after the cataract operation. The results were subjected to a statistical analysis with 3-factor anova. The cataract operation induced a significant increase of tear flow. Independent of this effect, administration of the carboanhydrase inhibitor caused a significant decrease of tear production, both in the operated eyes and the untouched fellow eyes.

Acetazolamide↗
PubMed1985

[Initial experiences in the treatment of changes in the anterior eye segment with the neodymium:YAG laser].

The present paper reports the first results with the Meditec OPL-3 neodymium:YAG laser (Rodenstock, Munich). The YAG laser is a pulsed laser, the biological effects of which are based on the formation of plasma at its focal point. Plasma formation induces a rapid explosion-like expansion of the tissue. This effect can be used to sever opaque structures of the refractive media of the eye, such as secondary cataracts, membranes or strands. The paper summarizes the results of the first 80 consecutive cases treated with the laser. The surgical procedure is described in detail. Visual acuity improved instantaneously in all cases in which no concomitant eye pathology (e.g., corneal or macular changes) existed. Complications consisted in the development of postoperative inflammatory reactions and increases in intraocular pressure, and responded well to corticosteroids and beta-blockers or Diamox. The development of the neodymium:YAG laser has considerably advanced our therapeutic possibilities.

Aged↗
PubMed1984

Effect of 8-methoxypsoralen on rat lens cations, membrane potential and protein levels.

Systemic application of 8-methoxypsoralen to rats, followed by u.v.-irradiation, induces a minor change in the lens membrane potential after one week, and by this time marked histological changes have already occurred. Alterations in lens sodium and potassium concentrations followed these early changes and coincided with the appearance of small light-scattering vacuoles when the lenses were examined in vivo with a slit lamp. Dramatic changes in the dry weight, soluble protein and calcium content of the lenses were apparent only after eight weeks from the start of treatment, and these changes coincided with the appearance of very large vacuoles in slit-lamp examinations of the eye.

Animals↗
PubMed1983

[Development of hypertension and cataract in spontaneously hypertensive rats].

The investigations were performed on 3 groups of untreated, spontaneously hypertensive Wistar rats of the Okamoto line. All the rats in Group I developed arterial hypertension within 16 weeks of birth and 33 percent of them developed cataracts within 22 weeks. Reserpine application suppressed hypertension and cataract development in all the animals in Group II. After unilateral adrenalectomy and contralateral adrenal enucleation (Group III), hypertension and cataracts developed in both treated and untreated animals; in the former, however, blood pressure was about 10 percent higher and cataracts developed about 6 weeks earlier than in the untreated rats. These findings support the hypothesis that arterial hypertension may be involved in cataract development.

Adrenalectomy↗
PubMed1982

8-methoxypsoralen and long ultraviolet effects on the rat lens: experiments with high dosage.

The effect of systemic 8-methoxypsoralen (8-MOP; 100 mg/kg daily) and subsequent long ultraviolet irradiation (UVA; 300 mJ/cm2; peak: 365 nm) on albino and pigmented rat eyes was studied in a 3-dimensional experimental set-up. While 8-MOP and UVA did not cause any ocular pathology when administered alone, a combined application of the two factors caused reversible corneal opacities, and irreversible iris devascularisation and cataracts. The irreversible changes were seen only in the albinos and accompanied by a significant decrease in lens wet weight. Phosphorescence and EPR spectroscopy demonstrated the formation of an 8-MOP-protein photoadduct in the animals treated with both 8-MOP and UVA. The results of this study emphasize the necessity of shielding the eyes of patients on photochemotherapy with protective spectacles.

Animals↗