Search PubMed⌕ Search

Biomedical subjects

R Birngruber

Publications and source records attributed to R Birngruber.

At least 109 records · Page 6Linked to original sources
PubMed1989

Picosecond optical breakdown: tissue effects and reduction of collateral damage.

The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage.

Animals↗
PubMed1989

Laser output characteristics.

Certain aspects of laser radiation play an important role in laser safety. After a short description of basic laser principles, the unique characteristics of laser light are explained in a phenomenological manner. The enormously wide range of laser output parameters is demonstrated and correlated to typical medical laser applications. Temporal and spatial modes of laser operation are explained in greater detail because of their importance in laser safety.

Humans↗
PubMed1989

Clinical observations of six cases of laser injury to the eye.

During the last decade, five patients with laser injuries were examined at the University of Munich Eye Clinic, in addition to one laser-injury patient at the University of Erlangen Eye Clinic. From a review of these cases, it is possible to gain an insight into factors that led to the eye injuries and to predict the clinical sequelae of laser retinal injury. A possible means of treatment, using an ophthalmic Q-switched Nd:YAG laser, is suggested for some types of retinal injury involving vitreal hemorrhage.

Accidents, Occupational↗
PubMed1989

[Quantification of the wavelength dependence of laser-induced choroid coagulation].

The penetration depth of laser light into the fundus is dependent on the wavelength. Thereby, the profile of damage depends on the absorption and on the temperature profile. It has been demonstrated earlier that wavelength-dependent differences in penetration depth are hard to detect ophthalmoscopically or histologically in severe lesions in Chinchilla gray rabbits. Therefore in this study, the wavelength-dependent exposure powers necessary for (1) similar retinal effects and (2) similar choroidal effects were compared. The resulting wavelength-dependent differences were smaller than expected-due to at least three reasons: (1) predominance of the temperature profile over the absorption profile for clinically useful exposure times; (2) light scatter in the retina in relationship to the exposure time (and wavelength?): (3) changes in the choroidal geometry in relationship to the exposure time and wavelength. Nevertheless, it appears to be possible to spare the retina somewhat by using longer wavelengths. In order to evaluate the clinical situation experimentally despite the fact that the human choroid is about three times thicker than the rabbit choroid, a geometrical model has been developed. The results indicate that the retina is less damaged using Nd:YAG lasers than using argon lasers when similar choroidal effects are produced.

Animals↗
PubMed1986

[Clinical relevance of a dosage device for laser photocoagulation].

Fundus reflectometry constitutes a procedure with which dosage can be precisely regulated during the coagulation process. During retinal coagulation, for example, it is possible with this method to administer coagulations of uniform intensity regardless of variations in either the quality of the fundus image or the absorption of the pigmented structures. This can be useful for coagulation procedures which have to be confined for the most part to the pigment epithelium, as for example in the treatment of central serous retinopathy or in panretinal photocoagulation, where the functional therapeutic principle is still not clearly understood. Another area of application for reflectometric laser coagulation will be laser trabeculoplasty, in which barely detectable lesions have to be placed in the trabecular meshwork.

Computers↗
PubMed1985

Theoretical investigations of laser thermal retinal injury.

A thermal damage model including heat conduction for retinal lesions is described to explain thermal threshold damage and compare it to experimental values in the regime of 1 ms to 300 ms. With the aid of these model calculations unspecific thermal damage (denaturation of proteins) could be separated from thermally induced damage to the photoreceptors. Furthermore, the thermal model allows an extrapolation to hazards to the fundus from intense light irradiation that have not been investigated experimentally.

Animals↗