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Biomedical subjects

R Birngruber

Publications and source records attributed to R Birngruber.

At least 145 records · Page 8Linked to original sources
PubMed1977

Fundus reflectometry: a step towards optimization of the retina photocoagulation.

A method is described for monitoring the light reflected from exposed areas during and after argon laser photocoagulation of rabbit eyes. The light serves as a measure of the retinal blanching and thus of the tissue reaction. It is shown, that the reflected light changes its time-dependent behavior qualitatively if hemorrhages occur. The energy necessary for a therapeutic coagulation is shown to decrease with decreasing exposure time as does the therapeutic band width for clinical coagulations. A relationship between exposure time and therapeutic band width was found and is discussed.

Animals↗
PubMed1977

Q-switched ruby laser damage of the rabbit eye lens.

Results on Q-switched ruby laser damage to lenses of Chinchilla grey rabbits are reported. Threshold irradiances of about 10(10)W/cm2 are shown to be necessary for lens damage. The minimal lesions consist of empty bubbles about 1 mm in diameter. Energy consideration as well as histologic investigation of the lesions indicate a mechanical damage process following a light-induced absorption in the focus. Retinal damage accompanied lenticular damage in all cases

Animals↗
PubMed1976

[Diathermy procedures, light and laser coagulation, cryocoagulation. Experimental and clinical considerations].

The clinical and experimental results from the methods of coagulation currently in use are presented. The advantages and disadvantages of trans-scleral methods (diathermy and cryopexy) and trans-ocular methods (Xenon arc and argon laser) are discussed. Experiments on absorption, the mode of action of intense light, the optimal time and method of application, the necessary intensity and the extent of the coagulated area are communicated. Of the trans-scleral methods, cryopexy is to be prefered. The trans-ocular methods have the advantage of a more exact localisation and dosage. Either route can often be chosen in any particular case, though at present no overriding advantage has been shown for either.

Cryosurgery↗
PubMed1975

Low intensity argon laser coagulation in central serous retinopathy (csr).

Mechanisms of light coagulation effects in RPE and detached retina are discussed. 25 cases of CSR are presented in which the leaking point in the RPE was coagulated with an argon laser coagulator, the exposure parameters being set to avoid a whitening of the retina. The results suggest that the retinal whitening and consequently retinal damage does not constitute a criterium for coagulation effectiveness in CSR.

Adult↗
PubMed1975

[Retinal reactions to intense light. I. Threshold lesions. Experimental, morphological and clinical studies of pathological and therapeutic effects of laser and white light].

The effects of intense light produced by an argon laser, a helium-neon laser and a xenon are photocoagulator in the retinas of gray chinchilla rabbits, cynomolgus monkeys, and rhesus monkeys were studied clinically and histopathologically including electron microscopy. An improved experimental set-up was used allowing a very good consistency of the inflicted lesions. Threshold lesions were produced in chinchilla rabbits and cynomolgus monkeys by an argon laser and a helium-neon laser. The lesions were evaluated ophthalmoscopically and histograms were drawn indicating ophthalmoscopic ED50 values. For the two lasers examined these values were 12 and 17 mW, respectively, for exposure durations in the range of the blink reflex (125-150 msec). Histopathologically, ophthalmoscopic threshold lesions of both laser types showed evidence of thermal damage of the outer retinal half. This damage was principally identical in both species involving the retinal pigment epithelium and the full extension of the photoreceptor cells up to their synapses within the outer plexiform layer. The ophthalmoscopic threshold value was associated, therefore, with an irreversible loss of visual function within the retinal area concerned. No evidence for primary sites of significant energy absorption within the neural retina was found. The width of ophthalmoscopic threshold lesions was determined by measuring within the histologic sections with a microscope and a calibrated graticule the extension of damage at the level of the retinal pigment epithelium and at the level of the outer nuclear layer. In the cynomolgus monkey for ophthalmoscopic argon laser threshold lesions the extension at the level of the RPE was 70-80 mum in diameter and at the level of the outer nuclear layer it was 40-50 mum in diameter. Laser lesions that had a diameter of 60 mum at the level of the RPE and of 30 mum at the level of the outer nuclear layer were ophthalmoscopically subvisible. It is concluded that probably also in man such laser lesions, as well as various other pathologic changes of this size or smaller, cannot be evaluated by clinical ophthalmoscopy. The ophthalmoscopic threshold was correlated with a histopathologic threshold as defined by minimal histopathologic damage. Very likely, such damage lies within the range of functional recovery, and the histopathologic threshold demarcates at the same time the decisive functional threshold. The conversion ratio between histopathologic-functional and ophthalmoscopic threshold for argon lesions in cynomolgus monkeys was somewhat greater than 3, e.i. the ophthalmoscopic threshold was more than 3 times higher than the histopathologic-functional threshold. Using this data together with additional biologic and optical considerations, a safety threshold for man for cw-lasers within the visible spectrum was estimated to be 1-2 mW.

Animals↗