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Biomedical subjects

F Fankhauser

Publications and source records attributed to F Fankhauser.

At least 145 records · Page 8Linked to original sources
PubMed1980

[Effect of a silicone band on the sclera of the human eye - morphological analysis].

Sixteen months after application of an encircling silicon band the morphological condition of the sclera was analysed. The findings were as follows: 1) The silicon band is highly compatible with the sclera and dose not produce a foreign body reaction. 2) The sclera is able to adjust to altered mechanical conditions produced by degenerative and regenerative processes. 3) The polyamide suture material was at least partially unchanged 16 months after implantation but had led to a strong foreign body reaction. The large number of cells containing enlarged polymorphic lysosomes indicate an attempt to break down the polyamide fiber enzymatically by localized cell reactions.

Humans↗
PubMed1980

[A statistical program for determining fields of vision (author's transl)].

Statistical tests, oriented towards optimum distinction between normal and abnormal behavior, may be applied to the results of static perimetric examinations. Such tests are also important for establishing whether significant progression has occurred. A prototype version of an analytical program is presented here; it evaluates the data stored in the memory of the automated perimeter Octopus. Statistical decisions are printed out in verbal form. Reservations regarding conclusions are discussed. Correlated long-term fluctuations in thresholds complicate the separation of true progression from insignificant coincidence.

Computers↗
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

[Reparative processes of the iris after irradiation with the argon-ion laser (author's transl)].

The reparative processes of the pigmented iris of the rabbit were analysed with ultrastructural methods. 1. Clearing of the damaged area by macrophages is the first step in the reparative processes. Clump cells are macrophages which are observed from the first day of the injury until the ninth week. 2. Repair of the anterior surface of the iris is largely finished after 32 days. 3. The repair of collagenous fibres reaches its maximum activity 32 days after irradiation. 4. The pigment epithelium has only an insignificant regeneration potential. 5. Irradiation of the iris by the argon-ion laser results in an atrophic, hyperpigmented scar. The rapid regeneration of a lesion induced by the argon-ion laser in the rabbit iris casts doubt as to whether this method could be applied to the human eye with equal success.

Animals↗
PubMed1979

The ultrastructural features of laser trabeculopuncture and cyclodialysis. Problems related to successful treatment of chronic simple glaucoma.

Microexplosions induced by a Q-switched Nd:glass laser working above optical breakdown power density levels are able to destroy the inner wall of Schlemm's canal and to tear open both the supraciliary and suprachoroidal space. Furthermore, the ciliary muscles bundles may be disrupted, becoming subsequently permeable to the aqueous and thus also acting as a new outflow route. However, whereas breaks of the inner wall of Schlemm's canals are sealed in the monkey by the activity of endothelial cells forming a new Descemet membrane over the impact site, the supraciliary and suprachoroidal spaces remain open over an observation period of up to 480 days. Perfusion experiments with a HgS tracer substance have shown that these newly created, potential outflow routes may be considered as real additional filtration areas.

Animals↗
PubMed1979

[Morphology of the primary damage caused by the argon-ion laser to the iris of the pigmented rabbit (author's transl)].

The effects of the argon-ion laser upon the iris of the pigmented rabbit were analysed by ultrastructural methods. 1. Apart from the physical parameters of the energy source, the damage strongly depends on the concentration, location, and distribution of the iris pigment. 2. The irradiation of the iris results in the formation of a crater. Depending on the distance of the epicentre of the impact, various degrees of ultrastructural damage are observed. a. The region immediately adjacent to the crater lumen at a revealing distance of 25 microns consists of homogenous collagenous masses, revealing a vacuolar structure. As the only residuals of destroyed cells, melanin granules are observed within the homogenous masses. b. Destruction of the collagen fibrils and their disintegration into subfibrils with elimination of all cell compartments is found in an area ranging from 25 microns to 300 microns from the wall of the crater. c. Damage to the chromatin structure is visible up to a distance of 300 microns to 375 microns from the wall of the crater. 3. Characterised by an invasion of macrophages into the damaged area, the cleaning phase starts 24 h after irradiation. 4. The results of this experiment indicate that because of the great energy dose required for man with the inherent widespread tissue damage and low probability of a lasting iridectomy, the cw argon-ion laser appears to be an unsuitable energy source for clinical iridectomy.

Animals↗
PubMed1979

[The morphology of the iris (author's transl)].

Scanning electron microscopy provides new information about the ultrastructure of the iris. The anterior surface of the iris, oriented towards the anterior chamber, is covered with a single layer of mesenchymal cells. Openings between the dendrite-like branching extensions of these cells form communicating channels between anterior chamber and stroma. The collagen fibres of the iris stroma are organized as rather tightly packed two-dimensional networks. The meshes of these networks form channels, oriented in an anterior-posterior direction, reaching the vessels of the iris. These vessels are wrapped by a tightly packed fibrous coating, consisting of collagen fibres which embrace the vessels in a helical fashion. It is assumed that the transiridial convection current acts as part of a temperature regulating mechanism.

Connective Tissue↗
PubMed1979

[The effects of the xenon arc lamp upon the iris of the pigmented rabbit eye (author's transl)].

The ultrastructural alterations of 10 pigmented rabbit irides 15 minutes to 257 days after irradiation with a xenon arc lamp were analysed. Pulse duration was varied while irradiation power was kept constant at 3.24 W. 0.32 J (= 100 ms pulse duration) were delivered to the left eye and 3.2 J (= 1 second pulse duration) to the right side. The area of damage event was considerably smaller at the lower energy level. However depth of the crater was the same at both higher and lower levels. Cells and organelles disintegrate forming lamellar structures and coarse granules. The shape of the pigment granules remains intact. Collagen fibres disintegrate into subunits loosing their periodicity. Mesenchymal cells cover the area of damage few days after irradiation at the low energy level. A thin scar remains at the impact site. High energy irradiation shifts the equilibrium towards degenerative phenomena. Secondary degenerative processes are powerful enough to induce a total decay of the iris substance. The reactivity of the iris irradiated by a xenon arc lamp thus depends from either irradiation duration, power level or from both (energy).

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

[The effects of a new type of laser on fixed tissue of the angle of the anterior chamber in the monkey eye (author's transl)].

Segments of fixed tissue of the chamber angle of the monkey eye are irradiated with a neodymium (YAG-) q-spoiled laser at a pulse duration of 50 ns, a pulse energy of 200 mJ and an optic distance of 15 mm. Perforating injuries are observed between the anterior chamber and Schlemm's canal. When an acute angle of the laser beam relative to the cornea is chosen, the application point must be at the anterior part of the trabecular meshwork, close to the cornea, to open the canal of Schlemm. An impact further back toward the iris would create cyclodialysis.

Animals↗
PubMed1978

[Long term observations after irradiation of the iris by the argon laser (author's transl)].

Eleven pigmented rabbit irides were irradiated with the argon laser and were examined electron-microscopically at several intervals between 15 minutes and 256 days after exposure. It was shown that cells start to migrate into the area of the lesion already on the fourth day. After 32 days the area of the lesion is completely closed. 256 days after exposure only a slight impression remained on the anterior surface of the iris.

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↗