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Biomedical subjects

E Spoerl

Publications and source records attributed to E Spoerl.

18 recordsLinked to original sources
PubMed2005

[A new treatment of keratectasia after LASIK by using collagen with riboflavin/UVA light cross-linking].

BACKGROUND: Keratectasia is one of the most severe complications after refractive laser surgery. Usually penetrating keratoplasty is the treatment of choice to achieve an optical rehabilitation in such cases. PATIENTS AND METHODS: We report on a female patient who developed keratectasia in both eyes 4 weeks after LASIK. Due to a severe keratectasia 10 months after LASIK, a treatment with riboflavin/UVA cross-linking was performed. RESULTS: Due to the induced collagen cross-linking the biomechanical status of the cornea was stabilized and a progression of the keratectasia was prevented. The postoperative refraction and corneal topography have been stable for 18 months. CONCLUSION: Collagen cross-linking leads to a stiffening of the anterior parts of the corneal stroma. The increase of biomechanical stability can stop the progression of a keratectasia after LASIK by means of a simple procedure.

Adult↗
PubMed2004

Keratocyte cytotoxicity of riboflavin/UVA-treatment in vitro.

PURPOSE: Collagen crosslinking using ultraviolet- A (UVA) -irradiation combined with the photosensitizer riboflavin is a new technique for treating progressive keratoconus. It has been shown to increase effectively the biomechanical strength of the cornea and to stop or even reverse the progression of keratoconus. As part of a safety evaluation, the present study was undertaken to investigate in vitro the possible cytotoxic effect of combined riboflavin/UVA-treatment on corneal keratocytes and to compare it to UVA-irradiation alone. METHODS: Cell cultures established from porcine keratocytes were treated with 0.025% riboflavin solution and various UVA (370 nm)-irradiances ranging from 0.4 to 1.0 mW/cm2 and with UVA alone between 2 and 9 mW/cm2 for 30 min. The cell cultures were evaluated for cell death 24 h after irradiation using trypan-blue and Yopro-fluorescence staining. RESULTS: An abrupt cytotoxic irradiance level was found at 0.5 mW/cm2 for keratocytes after UVA-irradiation combined with the photosensitizer riboflavin, which is 10-fold lower than the cytotoxic irradiance of 5 mW/cm2 after UVA-irradiation alone. CONCLUSIONS: A cytotoxic effect of combined riboflavin/UVA-treatment on keratocytes is to be expected at 0.5 mW/cm2, which is reached in the clinical setting in human corneas down to a depth of 300 microm using the standard surface UVA-irradiance of 3 mW/cm2.

Animals↗
PubMed2000

Manifest diabetes and keratoconus: a retrospective case-control study.

PURPOSE: To assess the influence of diabetes on the development of keratoconus to show whether biomechanical effects are also reflected in epidemiology. The two diseases have opposite impact on the biomechanics of the corneal stroma: manifest diabetes stiffens the cornea, whereas keratectasia weakens the tensile strength of the stroma. METHODS: The retrospective case-control study included files of 1,142 patients, with 571 patients in the case group (keratoconus patients) and 571 in the control group (clinical population). The groups were well matched with respect to sex and age. We established the number of diabetics in both groups and compared it statistically by means of the odds ratio to determine whether diabetes can be interpreted as having a "protective effect" whether it is a "risk factor" for the development of keratoconus. RESULTS: Two patients of the keratoconus group had manifest diabetes that developed many years after the diagnosis of keratoconus, while nine cases of diabetes were found in the control group. Statistical analysis revealed a strong protective effect of manifest diabetes regarding keratoconus (odds ratio = 0.2195, P = 0.034). This effect was evident only in type II diabetes patients. CONCLUSIONS: The protective effect of manifest diabetes may be explained by the induction of cross-links in the stroma, preventing biomechanical weakening of the cornea. This study shows that different biomechanical changes can be superimposed and assume epidemiological relevance.

Adult↗
PubMed1998

Induction of cross-links in corneal tissue.

The aim of this study was to investigate the possibility of induction of cross-links in corneal tissue in order to increase the stiffness as a basis for a future conservative treatment of keratectasia. Collagenous biomaterials can be stabilized by chemical and physical agents. The epithelium of enucleated porcine eyes was removed. Eight test groups, 10 eyes each, were treated with UV-light (lambda=254 nm), 0.5% riboflavin, 0.5% riboflavin and UV-light (365 nm) blue light (436 nm) and sunlight, and the chemical agents-glutaraldehyde (1% and 0.1%, 10 min) and Karnovsky's solution (0.1%, 10 min). Strips of 5 mm in width and 9 mm in length were cut from each cornea and the stress-strain behaviour of the strips was measured to assess the cross-linking process. For comparison, ten untreated corneas were measured by the same method. Compared to untreated corneas treatment with riboflavin and UV-irradiation as well as weak glutaraldehyde or Karnovsky's solutions resulted in an increased stiffness of the cornea. The biomechanical behaviour of the cornea can be altered by glutaraldehyde, Karnovsky's solution, and with riboflavin and UV-irradiation which offers the potential of a conservative treatment of keratoconus. To optimize this effect further investigation is necessary regarding the dose-response and in-vivo application.

Animals↗
PubMed1975

Reversible permeability changes in the membrane of a yeast cell sugar compartment.

Sorbose uptake by Saccharomyces cerevisiae was increased 40 to 60% by glucose and other metabolizable sugars. Neither growth nor binding accounted for the increased uptake. However, accessibility of a restrictive intracellular compartment was increased as shown by counterflow and efflux measurements. Efflux from the compartment was more than doubled by glucose. This effect was reversed by washing and was prevented by iodoacetic acid and other inhibitors, but not by cycloheximide. No evidence was found for a facilitated transport system in the compartment membrane such as exists in the external cell membrane. It was concluded that sorbose crosses the compartment membrane by simple diffusion and that a reaction requiring the metabolism of sugars increases the permeability of the membrane. Arabinose and fucose entered and were lost from the compartment like sorbose, whereas dimethylsulfoxide was unaffected by the compartment. All three of these later compounds were bound by the cells when glucose was available in uptake suspensions. Binding was prevented by iodoacetic acid, but not by cycloheximide.

Arabinose↗
PubMed1971

Disruption of yeast membranes by methylphenidate.

Methylphenidate blocked sorbose uptake and loss by yeast spheroplasts and, at higher concentrations (30 mm), disrupted the spheroplasts. At still higher concentrations (70 mm), methylphenidate also ruptured the membranes of whole yeast cells; sorbose and materials absorbing at 280 nm were lost from the cells, and methylene blue stained them. Intracellular structures were extensively affected, as shown by electron micrographs, and were more sensitive to disruption by methylphenidate than the external membrane. N-ethylmaleimide and Ca(2+) enhanced the rupture of external membranes by methylphenidate.

Buffers↗
PubMed1971

Mannitol utake by Saccharomyces cerevisiae.

The uptake of mannitol, a nonmetabolized hexitol, by Saccharomyces cerevisiae was measured. Various characteristics examined include: effects of temperature on uptake, inhibition of uptake by uranyl nitrate, competition for uptake by glucose, counterflow of mannitol by glucose, and the affinity of mannitol for a carrier system as measured by a Michaelis constant. That energy is required for uptake was shown by a decreased uptake in the presence of energy inhibitors, by an increased uptake upon addition of energy sources, and by the absence of uptake under anaerobic conditions with no fermentable energy sources available. That mannitol is bound to some cellular constituent after it enters the cell was shown by its attachment to non-dialyzable cell fragments and by the lack of an osmotic response, both of which are consistent with a minimal efflux.

Azides↗
PubMed1968

Inhibition by methylphenidate of transport across the yeast cell membrane.

The influence of methylphenidate on glycolysis in yeast cells was studied to describe more fully the nature of the reactions in which this drug participates. CO(2) production and O(2) uptake of yeast cells was inhibited 75% by a 10 mm concentration of the compound. This effect, with glucose as a substrate, occurred at pH 7.0, but not at pH 4.5. Kinetic data indicated that the reaction was noncompetitive and complex; the methylphenidate effect on CO(2) production could not readily be reversed. Glycolysis by cell-free extracts was not inhibited at the 10-mm concentration, but was affected at 100 mm. Utilization of O(2) with maltose and ethyl alcohol as substrates also was reduced. Entry into the cells of a number of different carbohydrates and of glycine was inhibited to different degrees. The loss from suspended cells of materials absorbing at 280 nm was reduced, and the efflux of sorbose, arabinose, and lactose was decreased. Thus, transport into and out of the cells was inhibited and leakage, or permeability, was reduced. It is hypothesized that methylphenidate reacts with a cell membrane constituent, or constituents, and inhibits glycolysis by blocking sugar passage.

Arabinose↗
PubMedDate not supplied

Techniques for stiffening the cornea.

In keratoconus, corneal stiffness is decreased. The purposes of this study were to search for techniques to stiffen the cornea and to determine a dose-response relation. The stiffness of collagenous tissues can be increased by cross-linking. Cross-linking techniques--riboflavin and ultraviolet irradiation (365 nm, 2 mW/cm2, 45 min), glutaraldehyde of low concentration, and several aldehyde sugars--were tested on corneas of enucleated porcine eyes. The stress-strain relation was measured and compared to untreated corneas. Aldehyde sugars produced cross-links by nonenzymatic glycation only after a prolonged time (realized in diabetics). Riboflavin and UV seems to be a promising technique to stabilize the cornea by artificial cross-linking.

Aldehydes↗