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Biomedical subjects

F Fankhauser

Publications and source records attributed to F Fankhauser.

At least 37 records · Page 2Linked to original sources
PubMed1995

Irradiation of rabbit retina with diode and Nd:YAG lasers.

AIMS: This study was carried out to compare the effects of continuous wave infrared laser radiation on pigmented and albino rabbit retinas at two wavelengths: 810 nm (diode) and 1064 nm (Nd:YAG). METHODS: Transpupillary laser pulses were applied with a spot size of 200 microns and durations of 200 ms (pigmented rabbits) and 0.5-1 s (albino rabbits). Light and electron microscopic analyses were performed immediately after exposure. RESULTS: In pigmented rabbits, threshold lesions were induced using a power of 100 mW with the diode and 200 mW with the Nd:YAG lasers. Damage was incurred by the retinal pigment epithelium with extension into the superficial and mid choroid posteriorly and into the outer retina anteriorly. In albino rabbits, lesions of comparable anteroposterior extension were identified using a power of 10 W with the Nd:YAG laser. Using diode laser irradiation, a maximum power output of 1.2 W failed to produce discernible lesions. CONCLUSIONS: The observed patterns of morphological damage are produced by complex tissue radiation interactions. In pigmented animals, this was primarily related to absorption of radiant energy by melanin within the retinal pigment epithelium and the choroidal melanocytes. In albino rabbits, laser induced effects occurred as a consequence of multiple scattering, together with absorption within haemoglobin and possibly also within tissue water. The data obtained provide further insight into the biological mechanisms arising from retinal photocoagulation with near infrared lasers.

Acute Disease↗
PubMed1995

[Critical thoughts on current laser surgery of the cornea].

OBJECTIVE: To analyze critically refractive surgery of the cornea by excimer laser and to compare laser surgery with other methods of treatment of refractive errors of the eye. MATERIAL AND METHODS: This analysis has to be restricted to a comparison of the treatment of myopia by keratotomy and photoablation with the ArF excimer laser. Correction of hypermetropia and of astigmatismus has to be left out, along with all the other methods to correct myopia, such as glasses, contact lenses, keratomileusis, epikeratoplasty, alloplastic implants, implantation of intraocular lenses with negative power, and replacement of the clear lens by an posterior chamber lens. The essential literature is screened. For intrastromal ablation with the picosecond Nd:YLF laser we relay on own experiences, also with the use of the ArF excimer laser we are not without own experiences. RESULTS AND STATEMENTS: For comparison of refractive surgery of the cornea not only the PERK study and the recommendations of the American Academy of Ophthalmology have to be considered, but also the newest developments in radial keratotomy such as two-step incision and reoperation with reopening of the keratotomy wounds. With these techniques the same precision can be reached as with the excimerlaser, and also higher myopias can be corrected. The dangers of the procedure, such as infection, perforation at surgery or laceration by contusion remain much larger. Intrastromal photoablation did not reach clinical maturity. Superficial photoablation is an almost safe procedure. A reduction of 3 D of myopia can be reached with satisfying precision, although higher myopias are still a problem. Pain following the ablation is considerable. Haze and disturbed vision at night can be present; infectious keratitis is rare, but possible. CONCLUSIONS: The critical fact of both procedures, keratotomy and photoablation with excimer laser, remains that healthy eyes are treated; therefore, even rare complications weigh much heavier than if sick eyes are treated. Because this is cosmetic surgery, the individuum asking for this type of procedure has to pay for on his own. Olson demands: "In determining when new technology is acceptable, we must consider the financial cost and the expected benefit to society. Is it an equitable tradeoff?" If we look at refractive surgery, especially laser photoablation, in the context of the needs for ophthalmic care of the whole world, then this type of surgery is out of proportion. The balance could be restored if, with every laser application, funds were given for third-world projects. Excimer-laser surgery may be justified insofar as the research with these lasers leads to useful therapeutic methods.

Follow-Up Studies↗
PubMed1995

Sclerostomy ab interno using long-wave laser modalities: acute morphological effects.

Sclerostomy fistulas were created ab interno in cadaver porcine eyes by an active contact method using a 200-microns-diameter silica optical fiber in conjunction with either Ho:YAG-, Nd:YAG-, or diode-laser light, and a qualitative comparison of the degree of collateral thermal damage induced in each case was undertaken at the light and electron microscopic levels. The apparent breadth of coagulated tissue observed in association with cross-sectioned fistula profiles exhibited considerable local variation, irrespective of the radiation source employed; no intrinsic difference in either the intensity or the extent of the thermal insult incurred was noted between the three laser modalities.

Animals↗
PubMed1994

A model for fluid mechanisms in sclerostomy.

The hydrodynamic mechanisms which subserve the outflow of newly created outflow canals in sclerostomy procedures are to a large extent obscure. The model presented here has strong analogies to a closed electric circuit and assumes that aqueous humor is pumped by the secretion pump into the anterior chamber, leaves the eye via the artificially created sclerostomy canal, and returns via the venous and arterial system to the ciliary body. The model attempts to describe the stationary situation which determines the intraocular pressure following sclerostomy in terms of the internal resistance of the secretion pump, the resistance in the sclerostomy canal, the resistance beyond the external ostium of the sclerostomy canal, the pressure in the anterior chamber, the pressure beyond the external ostium of the canal, and the secretion pressure exerted by the secretion pump.

Anterior Chamber↗
PubMed1994

[Sclerostomy using various laser modalities. Ultrastructure of acute effects].

The effects of Ho:YAG- (free-running mode), Nd:YAG- (continuous wave mode) and diode- (continuous wave mode) laser radiation on the degree of collateral thermal damage realized during the creation of sclerostomy canals ab interno (by an active contact method) were compared morphologically: Both the nature and extent of coagulation occurred by scleral collagen fibrils were found to be independent of the laser modality employed.

Animals↗
PubMed1994

[GRIN-endoscopy for laser treatment in ophthalmology].

Endoscopes for use in ophthalmology can be manufactured with diameters smaller than 0.89 mm. Because gradient-index (GRIN) lenses yield a higher resolution than ordered fiber bundles having the same diameter, GRIN lenses with a diameter of either 0.35 mm or 0.50 mm were utilized to manufacture thin high resolution endoscopes. Whatever the working distance, the resolution obtained with a GRIN lens having a diameter of 0.50 mm was higher than that obtained with a GRIN lens of 0.35 mm. Thanks to the miniaturization, an additional working channel could also be integrated within the endoscope. This allowed new combinations of various surgical instruments. This channel can be used as a guide for an optical fiber for laser therapy or as an irrigation/aspiration channel. The use of such an instrument where the observation path is parallel to the surgical instrument was compared to the application of the endoscope as a separate monitoring system. The advantages and inconveniences of both systems are discussed. Preference is given to a system where the diameter of the observation channel is maximum and the optical fiber for laser delivery is integrated but adjustable along its length within the endoscope.

Endoscopes↗
PubMed1994

Optical and thermal mechanisms related to the design of laser sclerostomy.

Collateral, thermally induced structural damage during laser sclerostomy ab interno or ab externo was investigated theoretically and compared with experimental results. We show that collateral heat damage in contact strategies using fiber delivery is mainly due to heat conductivity following explosive ablation. Electron micrographs of perforated porcine eyes show that the damage is only weakly dependent on the laser wavelength. The experiments also demonstrate that simultaneous application of laser irradiation and pressure with the fiber tip yield efficient perforation of scleral tissue even when the weakly absorbed radiation of Nd:YAG or diode lasers is employed.

Animals↗
PubMed1994

Fluctuations of visual field interpretation related to cluster and scotoma analysis by one interpreter.

A total of 189 numerical printouts of the visual fields of 189 eyes of individuals either suspected of or verified as having glaucoma and displaying varying degrees of glaucomatous visual field damage were analyzed by one expert interpreter. The amount of clusters (or scotomas) was counted and delineated in each visual field under both a more stringent and a more liberal criterion. The interpretations of the visual fields differed significantly in both groups, as did the subjective certainty the interpreter allotted to his assessment. In the group of certain decisions, only 144 defects were assessed as opposed to 364 when a more stringent rather than a more liberal criterion was adopted. In uncertain cases, a reverse trend was observed, since only 11 as opposed to 324 defects were assessed when a more liberal rather than a more stringent criterion was adopted. Both trends may be explained by an increase in sensitivity at the expense of specificity (i.e., a change in the receiver-operating characteristic of the expert when the latter is pressed to change the criterion in a subjective cluster or scotoma assessment task). The ambiguity of the task and the difference in the criterion adopted by the interpreter significantly influences the assessment of normality and pathology, in particular its extent and spatial distribution.

Adult↗
PubMed1994

Hans Goldmann.

Explore the source record for details and available documents.

History, 19th Century↗
PubMed1994

Temporal summation measurements with the Octopus 1-2-3 perimeter.

Until recently, measurements of temporal summation required the construction of specialized instrumentation or the custom modification of an existing perimeter, which meant that such testing was unstandardized and relatively expensive. This precluded extensive use of this type of visual response testing, especially in a clinical setting. In an effort to change this situation, a personal computer (PC) program has been devised that makes use of a new interface for remote operation of the Octopus 1-2-3 automated perimeter. The program can be used to measure temporal summation at 1-5 locations in the visual field (0 degrees-30 degrees eccentricity) for 1-10 stimulus durations (5.6-999 ms) in the presence or absence of background illumination (10 cd/m2). Two auxiliary programs for analyzing the resulting data have been developed as well. Preliminary measurement trials were performed on four normal and two glaucomatous eyes at three test locations for ten stimulus durations in both the presence and the absence of background illumination. Ten examinations were carried out for each eye to reduce the effects of short-term fluctuations. The resulting temporal summation curves and the associated critical durations were similar to those found in the literature. No effect of disease on the critical duration was found (n = 2). With this program package, the effects of disease on temporal summation can now be tested using a commercially available instrument. To determine its clinical usefulness, though, investigations with larger populations will have to be made.

Chronic Disease↗
PubMed1993

A cluster and scotoma analysis based on empiric criteria.

From a collection of 288 visual fields of glaucomatous or glaucoma suspects, 30 were selected at random and were analyzed by one expert interpreter. Visual field damage varied from nonexistent to severe. The interpreter defined clusters or scotomas subjectively according to adjacency criteria: adjacent test locations which exceeded a critical loss value were grouped as clusters or scotomas. A computer algorithm has been devised which simulates such evaluation methods. In general, a standard setting of several parameters produced a cluster display containing the same number of clusters as determined by the expert interpreter. Another display mode grouped clusters according to polygonal areas of a predetermined size (Voronoi diagram). Due to the broad selection of visual field defects, the specificity of the program with regard to various field decay patterns was small and it should thus be applicable to a broad spectrum of glaucomatous field damage.

Algorithms↗
PubMed1993

[Recollections of Hans Goldmann, 1899-1991].

Professor Hans Goldmann died in Bern on November 19th, 1991 at the age of 91 years. His outstanding intellectual capacity was discovered at an early age and demonstrated throughout his life. He was appointed as teaching assistant of the famous A. Cermak von Seysenegg, Chairman of the Institute of Physiology of the German Charles University in Prague. During his stay at the University of Prague, he was influenced by the famous people of his time, such as Einstein (physicist), Mach (physicist and psychophysicist), Lorenz (behavioral scientist), Popper (philosopher), Schlick (physicist and philosopher), Hering (physiologist), and others. Goldmann absorbed the essence of these disciplines to a very large extent. This, together with his remarkable intellect, enabled him to produce outstanding research work within a large spectrum of sciences more or less directly related to ophthalmology. Goldmann became known in particular for his exceptional and fundamental work on perimetry and glaucoma and he managed to cast his basic insight into practical, easy-to-operate, high-precision diagnostic instruments which, several decades after their invention, are still used by every ophthalmologist. He will enter history as one of the very great pioneers in ophthalmology.

History, 20th Century↗
PubMed1993

[Surgery with the laser scalpel. Physical principles and clinical effectiveness].

BACKGROUND: The conventional surgical method for cutting vascularized tissue with scalpel and scissors may now be improved by use of the laser scalpel. In particular, the frequent interruption necessitated and the poor visibility caused by bleeding may be mitigated owing to the haemostatic properties of laser light. This instrument may be of particular value for tasks involving extrabulbar structures, such as extraocular muscles and lacrimal tissue, as well as for facial surgery. MATERIALS AND METHODS: The mode of action and physical properties of a new laser scalpel are described and its characteristics compared with those of other instruments on the market. The probe consists of a clad, sculptured silica fibre with a core diameter of 0.6 mm and a conical 0.15 mm-diameter cutting tip. Radiation generated by a low cw-Nd:YAG laser module is fed into the probe, at the exit point of which a maximal power density of 57 kW/cm2 is attained. Radiated laser energy penetrates the tissue as an incision is made, thereby inducing an efficient blood flow stasis which is amplified by thermal energy diffusing from the immediate surroundings of the scalpel tip. RESULTS: In this report, the laser scalpel is implemented for the excision of a vascularized, amelanotic, facial naevus. Both the cutting and haemostatic effects were found to be excellent, occurrence of the latter phenomenon being supported by ultrastructural findings. The healing response was comparable to that observed after conventional surgery. CONCLUSION: The new laser scalpel represents an inexpensive and effective cutting and haemostatic tool powered by a standard cw Nd:YAG laser module, with a wide spectrum of potential applications.

Aged↗
PubMed1993

The role of laser cyclocoagulation in cyclodestructive glaucoma surgery.

As a last-resort, antiglaucomatous procedure, laser cyclodestruction continues to attract attention. Whether this approach will be applied at an earlier stage in patients with glaucoma remains to be seen, although this procedure is already used in patients who refuse or do not tolerate surgery. The success rate of this procedure will improve as our understanding of the underlying mechanisms that contribute to intraocular pressure reduction are more thoroughly realized, and as safety improves with increased sophistication of instrumentation.

Aluminum↗
PubMed1993

Versatility of the cw-Nd:YAG and diode lasers in ocular surgery.

The effectiveness of cw-Nd:YAG and diode laser light in performing transscleral chorioretinal coagulation is demonstrated in cadaver porcine eyes using a new contact probe that facilitates irradiation of these layers. Both radiation sources also may be viable alternatives to argon laser light in effecting chorioretinal and cycloendocoagulation.

Animals↗