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H Bebie

Publications and source records attributed to H Bebie.

13 recordsLinked to original sources
PubMed1979

Morphological studies about the efficiency of laser beams upon the structures of the angle of the anterior chamber. Facts and concepts related to the treatment of the chronic simple glaucoma.

Working at a power density above optical breakdown threshold, irradiation effects upon the angle of the anterior chamber of the Macaca speciosa monkey by a Nd glass Q-switched laser, have been analysed with scanning electron microscopy. Two different damage effects can be identified: openings of Schlemm's canal and the creation of a cyclodialysis, that is opening the uveoscleral outflow routes; the latter may be a more effective one than the former. Also a third mechanism, namely a structural alteration of the trabecular meshwork, at the molecular level by laser action, has been inferred. The physical effects leading to optically induced mechanical damage are discussed. Applicability of such effects upon the morphological findings described here, is limited and to a greater part speculative. A better definition of the physical parameters, required for optimal therapeutical damage effects in the treatment of the wide angle glaucoma may be obtained by trial and error methods, which are guided by the results of electron microscopical analyses of samples obtained from in vivo and in vitro experiments.

Animals↗
PubMed1979

[The effects of a gigant-pulse-laser upon the iris of the pigmented rabbit eye (author's transl)].

The eyes of 10 pigmented rabbits were irradiated by a Q-switched Nd:YAG laser. The pulse energy delivered to the right eye was 187 mJ while the left eye was irradiated with 58 mJ. The pulse duration in both cases was 25 ns. The destructive effects were analysed for two different positions of the focus. In the upper half of the eye the focus was positioned at the anterior iris surface. In the lower half it was adjusted near the pigment epithelium. The eyes were analysed by electron microscopy at intervals of 15 minutes to 128 days after irradiation. The immediate effects were found to depend from the position of the focus but less from pulse energy. At later phases, tissue reaction depends from pulse energy. -- Scarification, at the lower energy level, is almost complete after 32 days. At the higher energy level, degenerative processi are setting in; 3 days after irradiation a progressing iris atrophy is observed which has not yet faded at the 128th day.

Animals↗
PubMed1978

On the effects of different laser energy sources upon the iris of the pigmented and the albino rabbit.

The irides of pigmented and albino rabbits have been irradiated by a) a CW argon laser beam (exposure duration up to 1 s), b) a 1 ms pulses Nd:YAG laser and c) a 30 ns pulses Q-switched ruby laser. The immediate and long-term pathologies were analysed by scanning and transmission electron microscopy over a period of 13 months. At both the gross and ultrastructural levels, damage configuration may differ considerably, depending on the three modes of irradiation. For each source there are both thermal and mechanical damage components and the significance of mechanical effects increases with decreasing pulse duration for a constant pulse energy. In the argon experiments, tissue destruction is predominantly a consequence of heat, resulting from conduction and convection. The subsequent regeneration of tissue after such heat-induced trauma is fast. The effects of the Nd:YAG laser, at the irradiance levels used in the present study, are again predominantly of a thermal nature and are caused by heating and local evaporation. The pigmented and the nonpigmented iris epithelium are destroyed and widespread decay of the stroma occurs over some months. Such damage never results in full repair. The most prominent feature of Q-switched ruby laser irradiations is their independence of the iris pigment content. In contrast, at the energy levels studied, the argon laser is entirely ineffective, whilst the effect of the Nd:YAG laser is much reduced in the absence of pigment. The consequences of these findings for the clinical applications of such lasers are discussed.

Animals↗
PubMed1978

[Practical experiences with the Octopus automatic perimeter (author's transl)].

A statistical analysis comparing the results of more than 1000 visual field examinations carried out with the automatic perimeter Octopus and with a conventional Goldman-perimeter, clearly demonstrates the superiority of the automatic instrument in many respects: Apart from a higher precision of the perimetric measurements (smaller fluctuations), a better reproducibility of the results (larger correlation coefficients) is noticed. Due to great ease of operation of the automatic perimeter, the ophthalmologist is discharged from the time-consuming task of perimetric examinations.

Computers↗
PubMed1976

Static perimetry: strategies.

In static perimetry the method of limits is widely used for threshold determinations. Its performance is compared with that of a certain modification of the staircase method (repetitive up and down) by means of simulations, where the behaviour of the observer is described by an assumed psychometric function. Systematic and random errors are considerably smaller with the up and down method. Further consideration is given to signal detection theory and to the concept of optimal strategy.

Humans↗
PubMed1976

Static perimetry: accuracy and fluctuations.

Threshold fluctuations are divided into short-term and long-term effects applying statistical methods. Sixteen normal and pathological visual fields were analysed in order to obtain values for the short-term, long-term and total fluctuations. Special attention is paid to fortuitous variations between the results obtained at successive examinations. Finally the concept of spatial correlations is introduced.

Humans↗
PubMedDate not supplied

Some aspects of the automation of perimetry.

Manual perimetry has certain inherent limitations stemming from both the patient and the examiner. Automated perimetry, if properly developed, can offer the advantages of exact reproducibility of the examination strategy, accuracy achieved through averaging of repeated determinations, and systematic application of previous data to the current examination. The history, concepts and clinical practically of automated perimetry are discussed. Several systems capable of performing functions resembling human intellectual activity are commerically available; one, the OctopusTM, is described in detail.

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