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Biomedical subjects

T Bende

Publications and source records attributed to T Bende.

At least 19 recordsLinked to original sources
PubMed1991

[Laser coagulation of the cornea with a holmium:YAG laser for correction of hyperopia].

We present a new technique of hyperopic correction similar to radial thermokeratoplasty. A pulsed Ho: YAG laser was used that emitted radiation at 2.06 microns and was guided by a quartz fiber and a focusing hand piece. The penetration depth of this light in the cornea is about 400 microns. Eight or 16 concentric point coagulations result in steepening in the central cornea. This refractive change is inverse related to the distance to the cornea center, and it increases linearly with increasing laser pulse energy. In four blind eyes it was demonstrated that the parameters evaluated in cadaver eyes can be transferred to living eyes. Surprisingly, the refractive change so created of up to 5 dpt is stable within a period of 4 months. Immediately after surgery, concentric descemet folds can be detected, which gradually decrease within the period reported.

Cornea↗
PubMed1991

[Photoablation with the Er:YAG laser in ocular tissues].

Photoablation of ocular tissues is not restricted to the excimer laser. Alternative tools are erbium lasers. As there is maximum absorption in ocular tissue at about 3 microns, two types of erbium lasers are capable of photoablation. One is the Er:YAG laser working at a wavelength of 2.94 micron; the other is the Er:YSGG laser emitting light with a wavelength of 2.79 microns. Both lasers produce higher ablation rates than the excimer laser. In comparison to the excimer laser (thermal damage of less than 1 micron), there is more thermal damage in the remaining tissue (3 microns). The lower ablation rate of the Er:YSGG laser due to the greater distance of the wavelength from the absorption maximum can be compensated by a higher output energy and a higher repetition rate (25 Hz). Wound-healing studies in rabbit corneas show no significant differences between the excisions performed with the Er:YAG laser and 193 nm excimer laser.

Cornea↗
PubMed1990

[Basic considerations on the use of the Excimer laser in dentistry].

SEM studies showed that irradiation in the energy density range of 4-6 J/cm2 resulted in the removal of hard tooth structure without causing thermal alterations of the tissues. In this process (photoablation) the natural structures of the tissues are "exposed". The surface structure thus produced in dentin depends on whether the dentin tubules are hit transversally or longitudinally and varies accordingly. The surface structure of enamel, as well, is determined by the alignment of the prisms. When the laser beam was optimally adjusted (energy densities of 4-6 J/cm2 and peripheral fading), no structural changes could be demonstrated in the depth of the tissue.

Dental Cavity Preparation↗
PubMed1990

[The ablation behavior of various corneal layers].

The difference in structure of the corneal layers leads to an inhomogeneous reaction to photoablation with 193 nm excimer laser light. This is important for the calculation of photorefractive keratectomy (PRK) where only a thin layer (10-50 microns) of the cornea must be removed. Therefore, the ablation rate for the Bowman zone is 2.5 times lower than that for corneal stroma; the same value is found in Descemet membrane. In contrast, the ablation rate of the epithelium is 1.5 times higher. Based on these data it will be possible to achieve high precision with PRK.

Astigmatism↗
PubMed1989

[Magnetic resonance tomography in ophthalmology. II. Manifestations of edema of the optic nerve].

MRI findings specific for lesions of the optic nerve are reported in the present paper for the first time: a dilated subarachnoidal space during the acute phase and scars in the neural tissue several months later. For imaging, the authors used special pulse sequences and surface coils. Twenty of 37 patients presenting with these symptoms were suffering from retrobulbar neuritis. In at least 12 (60%) of them the neuritis was associated with multiple sclerosis. Patients with tumors of the sella region usually have bilateral edema in the subarachnoidal spaces of both nerves. The edema is always located distal to the nerve lesion. The subarachnoidal edema is only of limited significance as a sign of optic neuritis. On the other hand, the authors failed to find a single case of neuritis without such edema.

Adult↗
PubMed1989

[Partial external trabeculectomy].

The authors show that with the Excimer laser partial trabeculectomy can be performed, a procedure in which the juxtacanalicular meshwork is removed while the other layers remain untouched. It was proved in experiments on ten enucleated human eyes that at most 3% of the outflow resistance is localized in the uveal and sclerocorneal meshwork. The clinical applicability of partial trabeculectomy was demonstrated on five eyes.

Choroid Neoplasms↗
PubMed1989

[Amelanotic melanoma and nuclear magnetic resonance tomography--case report].

In MRI choroidal melanoma shows a very short relaxation time (T2), shorter than that of any other intraocular tumor. This short T2 time is referred to the high concentration of paramagnetic melanine in this tumor. Therefore, it is of interest to measure the relaxation time in an amelanotic melanoma and compare it with the histological analysis. The duration of T2 for the amelanotic melanoma examined ranged from 130 to 160 ms. The small concentration of melanine is not a sufficient explanation, but it is possible that there are some precursors of melanine with paramagnetic characteristics.

Adult↗
PubMed1989

[Superficial ablation of the cornea using the excimer laser (193 nm)].

The final result of corneal surgery such as resection of the pterygium or lamellar keratoplasty is a rough corneal surface. Scanning electron microscopy shows that it is possible to obtain a smoother surface by using the 193 nm excimer laser, as it shows significantly better results than with conventional methods. This procedure was tested on eight patients and documented photographically.

Animals↗
PubMed1989

[Visual evoked cortical potentials modified by a NMR magnetic field of 0.24 Tesla].

The visual evoked cortical potentials (VECP) of ten persons with normal vision were investigated under the influence of a nuclear magnetic resonance (NMR) field with a magnetic field strength of 0.24 T. An increase in latency of 2.09 ms for the mean value was found with weak significance and a significant increase of 2.55 ms for the median under magnetic field influence. There were no remaining changes in the VECP after ceasing the magnetic field. The method and results are demonstrated and discussed.

Adult↗
PubMed1989

[Removal of hard tooth substance with Excimer lasers].

The usefulness of an Excimer laser (wavelength 308 nm) to remove enamel and dentin was assessed by examining the necessary energy flow density, micromorphological changes, and irradiated surfaces. Our results demonstrated that it is possible to remove dentin and enamel with the Excimer laser in controlled fashion. The temperature in the pulp cavity rose as a function of the distance to the site of irradiation (corresp. to distance between temperature measuring probe and irradiated tooth surface) and the duration of exposure and amounted to 3.5 degrees C-18.3 degrees C. Differences in the micromorphology of the surface structures were observed as a function of the material (enamel or dentin) and the duration of irradiation.

Dental Cavity Preparation↗
PubMed1989

[Usefulness of Excimer lasers in dentistry].

In vitro investigation on the influence of 308 nm excimerlaserradiation on extracted human teeth. Depending on the distance of the area of radiation to the pulp the temperaturerise ranged from 3.5 degrees C (6 mm) to 18.2 degrees C (less than 0.5 mm). REM investigations of radiated surfaces indicate a good retention of filling materials. TEM investigations of radiated dental hard tissues demonstrated that there is no structural change of the ultrastructure below the radiated surface.

Dental Restoration, Permanent↗
PubMed1988

Excimer laser keratectomy for correction of astigmatism.

We treated 13 eyes (12 patients) with excimer laser surgery for correction of astigmatism using linear corneal T-excisions. All eyes were followed up for a minimum of three months. We used a newly developed delivery system and special contact masks to deliver the 193-nm excimer light. Astigmatic corrections of up to 4.16 diopters were obtained. The actual corrections corresponded well with the intended values as predicted by a biomechanical theory. The refractive change over time was different than that observed after knife incisions, suggesting different repair mechanisms. An epithelial plug filling the whole T-excision persisted for over one year in all eyes.

Adult↗
PubMed1988

Side effects in excimer corneal surgery. DNA damage as a result of 193 nm excimer laser radiation.

UV radiation is known to cause actinic damage to the DNA. Excimer laser light, possibly used for keratorefractive surgery, should not produce this damage, as the penetration depth is far less than the diameter of a cell. However, photoreactivation experiments with yeast cells show a significant amount of DNA repair after excimer irradiation. The zone of influence of a small slitlike exposure has a diameter of 2 cm. Consequently, the limbus, the critical location of epithelial neoplasia, always lies within the sphere of actinic damage. Radiation damage is induced by secondary radiation rather than by direct interaction.

Cell Line↗
PubMed1988

Side effects in excimer corneal surgery. Corneal thermal gradients.

Thermal loading is a significant side effect during excimer laser surgery of the cornea. The maximal temperature rise, which is dependent on fluence and repetition rate of the radiation, amounts to 20 degrees C in excised corneas and 7.5 degrees C in the in situ cornea. The temperature decreases exponentially with increasing distance from the incision with a half-value distance of 610 +/- 100 micron. Exposure parameters are recommended to avoid temperature rises greater than 11 degrees C.

Animals↗