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Biomedical subjects

R Birngruber

Publications and source records attributed to R Birngruber.

At least 127 records · Page 7Linked to original sources
PubMed1984

Chemical studies of intraocular lenses after experimental generation of lesions by a short-pulsed Nd-YAG laser.

It is theoretically possible that lesions generated by a Q-switched Nd-YAG laser could lead to chemical changes in polymethylmethacrylate (PMMA) intraocular lenses. These changes could be of clinical relevance. Therefore, we measured the residual monomer content of intraocular lenses before and after generation of lesions by means of a short-pulsed Nd-YAG laser. Despite the explosive destruction of the lens surface caused by this type of laser, there is no measurable release of monomer in the sense of a depolymerization of the PMMA material, even when over 100 lesions are generated. The lesions generated on intraocular PMMA lenses with the Nd-YAG laser are predominantly of a mechanical nature and include the chipping away of small particles from the intraocular lens.

Lasers↗
PubMed1984

Vitreous morphology after carbon dioxide laser irradiation.

The immediate vitreous changes produced by a continuous-wave carbon-dioxide laser beam in freshly enucleated bovine and pig eyes were studied by gross examination with a dissecting microscope, and histopathologically by light microscopy and transmission electron microscopy. The lesions produced by the laser beam on the vitreous in an air tissue interface technique were remarkable for their ring-shaped vitreous condensations. The diameter and density of these condensations increased with irradiance. With the same irradiation parameters the lesions at the anterior hyaloid membranes showed greater size and density than those in the central area of the vitreous. These vitreous condensations were demonstrated to consist of heat-denatured collagen fibrils. For light microscopic evaluation of the vitreous a modified method of tissue processing according to Szent Györgi has proven optimal in reducing vitreous shrinkage from dehydration. This method of fixation and tissue processing appeared to be useful in evaluating lesions of the vitreous and their relationship to their surroundings.

Animals↗
PubMed1983

Experimental studies of laser thermal retinal injury.

In damage tests conducted on rabbit and monkey eyes, the threshold values for retinal damage resulting from different laser radiation were determined. The reproduction of the "worst-case" situation was ensured by the test apparatus. All physical parameters, such as power/energy, exposure time, and retinal spot, were carefully controlled. Probit analysis showed a very precise determination of the threshold values based on ophthalmoscopical visibility. The attempt of a simple physical interpretation of the thresholds leads to contradictions in major points, so a detailed calculation of damage functions and thermal model calculations are necessary.

Animals↗
PubMed1983

Thermal versus photochemical damage in the retina--thermal calculations for exposure limits.

Different kinds of damage can be produced by intense light irradiation of the retina. These types of damage can be separated into changes which are induced by photochemical or thermal effects in the tissue. Photochemical damage occurs mainly with intense irradiation of a few seconds or longer whereas thermal effects appear to prevail at irradiation times in the 1 ms to 1000 ms-range. Distinction between photochemical and thermal damage is very difficult because both types of injury appear as disorders in the retinal pigment epithelium and the outer segments of the photoreceptors. A thermal model has therefore been developed which takes into account the light absorption in the different layers of RPE and choroid and allows the calculation of the temporal development of temperature at each site and depth of the fundus. Model calculations are used to correlate exposure parameters (wavelength, irradiance, exposure time etc.) with the resulting temperature profiles. This correlation leads to a better distinction between exposure limits for thermal and photochemical damage of the retina.

Burns↗
PubMed1980

[Possibilities for ocular vessel coagulation (author's transl)].

Present-day possibilities of influencing pathological ocular vessels using an argon laser are presented. A distinction is made here between indirect methods such as area coagulation and direct methods with which specific vessels are treated. Whereas clinical tests involving vessel coagulation with pigmented epithelium absorption have already been carried out more or less successfully, selective vessel coagulation with hemoglobin absorption is still largely at the experimental stage. Our own experiments on animals have shown, however, that with the selection of a suitable coagulation technique and the use of suitable exposure parameters, vessel occlusion can be induced with the argon laser. To achieve this, shortening of the exposure times is particularly necessary.

Aged↗
PubMed1979

Minimal spot size on the retina formed by the optical system of the eye.

A knowledge of the quality of the ocular optical system is of primary importance in light- and laser-photocoagulation of the fundus. A study was therefore undertaken to determine the minimal spot size of a Helium-Neon laser focused on the retina of rabbits: freshly enucleated eyes were carefully mounted in a specially designed eye holder. A small hole was then trepanized through the sclera and neural retina in the macular region. A minimal spot was produced on the retina and the spot size was measured by scanning the intensity distribution of an enlarged image. It was shown that a diffraction limited spot size can be obtained under certain circumstances. The light scattering out of the focus, however, is about fify percent.

Animals↗
PubMed1978

Q-switched ruby laser induced damage of the adult rabbit lens capsule.

The technique of Q-switched ruby laser induced mechanical destruction of the lens capsule was used to study the reactions of the adult rabbit lens. The defect produced in the anterior lens capsule was larger than the 40-60 micrometer focus, which was due to rolled-up edges of the capsule. Long-term observations revealed some decrease in size of developing localized opacification and a healing of the defect by outgrowing lens epithelium with the formation of a new capsule. The rupture of the posterior capsule led to a slowly progressive opacification with little intraocular macrophage reaction.

Animals↗