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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
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↗
PubMed1982

Histologic observations of the lenses of psoralen + UVA treated albino rats and a theory as to the underlying mechanism.

Histologic studies of the lenses of 8-methoxy-psoralen and UVA treated rats revealed that morphologic damage appears first in the epithelium weeks before the onset of any slitlamp observable opacities. The bow region of the lens subsequently shows abnormal morphology, including rounded rather than elongating cells and a dramatic reduction in the number of nucleated fibres. With time, more and more of the cortex becomes involved, in the worst cases progressing to total liquifaction of the outermost cortex. The deeper cortex maintains an ordered pattern. Protected by the upper lid from UVA radiation, the upper lens is never as severely involved as the inferior lens. These findings are consistent with the hypothesis that the basis of the psoralen cataract is genetic damage to lens epithelial cells with subsequent formation of anomalous cortical fibres.

Animals↗
PubMed1982

[An ocular toxicity study with flupirtine as an example of evaluation of possible ocular drug side effects in human volunteers (author's transl)].

Animal experiments do not provide complete information on all the possible ocular side effects and the toxicity of a new drug. Several functional or dynamic parameters of vision can only be tested in humans as they are either do not exist in laboratory animals or their assessment requires a subjective contribution by the test person. A study was carried out on a new analgesic substance (Flupirtine) in which a large number of such parameters were tested in young healthy volunteers. The results were subjected to statistical analysis with a two-factor partlyhierarchical anova and no toxic effects were detected. The study shows how such parameters of visual function can be tested in humans.

Adult↗
PubMed1981

[Recurrent corneal swelling accompanying intermittent hemodialysis in terminal kidney failure (author's transl(].

Typical eye changes in dialysis patients, which have been attributed to an osmotic disequilibrium, are elevated IOP, retinal edema or detachment, and cataract. This paper reports on a 66-year-old aphakic patient on intermittent hemodialysis, who developed corneal changes that may also be consequential to a disequilibrium. During hemodialysis treatments she repeatedly developed corneal swellings and bullous detachment of the corneal epithelium. These changes were always reversible during the period between treatments. Examination with the reflecting microscope demonstrated an endothelial cell density of 600/mm2, which is assumed to be the threshold density capable of maintaining corneal integrity under normal conditions, but is inadequate under the osmotic stress induced by hemodialysis. Methods of treatment are discussed.

Aged↗
PubMed1981

[PUVA treatment and the problem of ocular damage (author's transl)].

Recently, psoriasis has been shown to respond favorably to PUVA treatment, i.e., local or systemic therapy with a photosensitizer (e.g., 8-methoxypsoralen) and subsequent long UV irradiation. The possibility of this treatment damaging the eye is discussed in the light of various experimental results. As toxic changes only occur when photosensitizer and UVA act jointly, the eyes of PUVA-treated patients must be shielded from any ultraviolet exposure by UV-absorbing protective glasses with side shields. Such glasses should have no significant absorption in the visible range. The new Spectra Shield process enables lenses to be coated in such a way that virtually no UV or IR radiation is transmitted.

Eye Protective Devices↗