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Biomedical subjects

F Fankhauser

Publications and source records attributed to F Fankhauser.

At least 127 records · Page 7Linked to original sources
PubMed1983

Contact glass for use with high power lasers--geometrical and optical aspects. Solution for the angle of the anterior chamber.

A new mirror contact glass for irradiation of pathological structures within the angle of the anterior chamber with high power lasers is described. The new contact glass is distinguished by its optimized optical characteristics. Due to its spherical front surface, tipping movements, as necessary in inspection and aiming manoeuvres, have no significant influence on the focus diameter. That the imaging quality is independent of the contact glass manipulations is seen as essential for laser surgical tasks with high power lasers, since changes in the focus diameter critically affect the power density at the focus and thus the intensity of the microsurgical effects. The increased spatial reliability of the laser-induced microexplosion is thought to be a further merit of the new contact glass.

Anterior Chamber↗
PubMed1983

Contact glasses for use with high power lasers. Two new contact glasses for microsurgery at the iris, in the pupillary and the retropupillary space.

Two new contact glasses, one for irradiation of the iris and the other for irradiation of pathological structures within the pupillary and retropupillary regions are described. First order geometric considerations using the Young-Weierstrass imaging theorem indicate nearly aberration-free, stigmatic focussing, even for large numerical apertures. For surgical tasks utilizing high-power lasers, excellent focussing of strongly convergent ray-bundles which lead to small focus diameter and large diameters while passing through the pre-focal optical media are seen to be essential. Thus the efficiency of the laser-surgical treatment, its reliability, as well as security and harmlessness within the pre-focal media are increased.

Humans↗
PubMed1982

Clinical studies on high and low power laser radiation upon some structures of the anterior and posterior segments of the eye. Experiences in the treatment of some pathological conditions of the anterior and posterior segments of the human eye by means of a Nd:YAG laser, driven at various power levels.

A Q-switched Nd:YAG laser apparatus has been used in the treatment of a number of pathological conditions of the anterior and posterior segments of the human eye. This laser system may be driven in a free running mode, thereby allowing variation of pulse duration over a range of 12 ns to 10 ms. With increasing pulse duration, non-linear mechanical damage patterns characteristic of the biological effects at the lower exposure duration range become unimportant when compared to the so-called thermal effects met at the upper pulse duration range. The thermal damage mechanisms may be useful when applied together with the mechanical damage mechanism, for instance when iris perforations are intended. Because the Wise-Witter irradiation method for the treatment of open angle glaucoma depends on low power, thermal mechanisms, this instrument may also be useful for the treatment of this disease entity. This same irradiation mode may also be applied to at least some irradiation tasks of the retina and choroid.

Choroid↗
PubMed1982

[Ultrastructure of the hyaloid canal and its retraction during gestation (author's transl)].

1. The cells of the hyaloid canal originate from the primitive meningeal cells; 2. The lumen of the hyaloid canal can be observed through the optic nerve up to the subarachnoid space around the optic nerve; 3. Injections of tracer substances into the subarachnoid space of the optic nerve have shown that a communication between the subarachnoidal space and the lumen of the hyaloid canal is formed up to the capsula of the lens during the first 14 weeks of gestation. It may be assumed that in vivo cerebrospinal fluid reaches the lens because of the hyperplastic differentiation of the choroid plexus in the sixth week of gestation; 4. The distal two-thirds of the hyaloid canal retract between the 17th and 22nd week of gestation; 5. From the beginning of the 22nd week of gestation there exists an open communication between the subarachnoid space and the corpus vitreum.

Eye↗
PubMed1982

Lasers in the treatment of chronic simple glaucoma.

Basic biological effects of laser irradiation are given with respect to the treatment of chronic simple glaucoma. As for the irradiation of the trabecular meshwork, an ultrastructural analysis of what is happening in the method of Wise and Witter (1979) has been done (a). In comparison with the effect of an Argon-ion laser (pulse duration 0.2 s, pulse power 2.2 W) upon the trabecular meshwork of human autopsy eyes the effect of a Nd:YAG laser (pulse duration 10 ms, pulse energy 2 J) has been analysed in ultrastructure. After cyclodialysis by Q-switched laser pulses the routes of outflow of the aqueous humour from the suprachoroidal and supraciliary space have been marked using mercury sulfide red (b). Three ways of outflow could be identified: (1) Into the veins of the ciliary body (2) Into the vortex veins (3) Into the subarachnoidal space around the optic nerve. The last way represents a communication between the suprachoroidal space and the cerebrospinal fluid.

Argon↗
PubMed1982

Future of the laser in ophthalmology.

A novel Nd:YAG laser apparatus, the Microruptor I, is presented in this study. The pulse duration of this system may be varied in steps from 15 ns, when driven in a Q-switched mode, up to 10 ms when driven in free running mode. When driven in Q-switched mode optical breakdown phenomena cause non-linear 'mechanical' destructive effects. The broad clinical spectrum of application in this mode is related to the ability to affect non-pigmented and transparent structures. In contrast to this, thermal tissue coagulations are to be found using the laser in the free running mode. Examples for clinical applications of the laser in both operation modes are shown.

Animals↗
PubMed1981

Clinical studies on the efficiency of high power laser radiation upon some structures of the anterior segment of the eye. First experiences of the treatment of some pathological conditions of the anterior segment of the human eye by means of a Q-switched laser system.

A series of pathological conditions such as pupillary block glaucoma, angle block glaucoma, acoria, pupillary membranes and goniosynechias of various origins have been treated successfully by means of pulses emitted from a Nd:YAG Q-switched laser above optical breakdown threshold. Since linear absorption is not required, non-pigmented or entirely transparent structures are easily dissected by this method. We have also opened the supraciliary and suprachoroidal space in a series of cases of wide angle glaucomas. In all cases however, the clefts closed by secondary wound reactions. This method may be applied to extracapsular cataract surgery for opening the anterior capsule before lens extraction and to the hydrophthalmic eye.

Cataract Extraction↗
PubMed1981

Programs SARGON and DELTA: two new principles for the automated analysis of the visual field.

The new Octopus programs SARGON and DELTA are described. The SARGON program makes possible the arbitrary distribution of a maximum number of 66 test locations with a resolution of up to 0.2 degrees across the 60 degrees visual field. Eighty user-defined self-created programs can be permanently stored and recalled later at will from the program diskette.. The program DELTA evaluates perimetric examination results with the aid of a series of statistical tests and investigates whether the data base is sufficient to assume a significant deviation, or alternatively, whether a visual field defect can be explained simply by spontaneous fluctuations or if a true pathologic defect should be assumed at a particular level of significance. Furthermore, the program tests changes in the visual field as a function of time for their statistical significance.

Computers↗
PubMed1981

Octopus programs SAPRO and F. Two new principles for the analysis of the visual field.

The automatic Octopus perimeter has a large software development potential. An important property of the Octopus programs developed to date is their ability to distinguish between pathological and normal behaviour. At the moment, program development is concentrating upon programs in which criteria of normality are used as feed-back parameters during the examination itself, and thus guide the visual field analysis. This property permits the algorithm to undertake a precise spatial analysis of disturbed visual field areas, without wasting time on a detailed analysis of normal areas. The efficiency of a visual field examination program is thereby substantially increased (SAPRO* program). Using the F-program series, individual (as opposed to fixed) stimuli configurations can be realised, which may represent a better fit to a particular problem. The principles of two other programs, SARGON and DELTA, have been described before (Fankhauser and Jenni 1981).

Computers↗
PubMed1980

Dynamic range and stray light. An estimate of the falsifying effects of stray light in perimetry.

The role of intraocular stray light upon contrast threshold of two skilled human observers was studied by perimetric methods using the automatic perimeter Octopus. Stray light falsifies the contrast sensitivity profile of the blind spot when a critical test stimulus luminance, which differs for various targets, is exceeded. At still higher test stimulus luminance, which differs for various targets, is exceeded. At still higher luminance levels, because stray light effects increase, the blind spot shrinks and finally disappears. A series of high resolution measurements of the blind spot with the automatic perimeter Octopus provide a quantitative answer concerning the commencement and amount of this disturbance as a function of target size and target luminance. The amount of stray light, when using targets varying from 0 to 5 (Goldmann standard) is related to luminous power (target luminance x target area). Using first order assumptions about the stray light emitting characteristics of the disc and empirical data, one may conclude that an increase in luminance of target 0 from 10(3) to 10(5) asb only increases the effective dynamic range by about 2 dB (= 0.2 log units 3, the standard target as compared with target) size used in Octopus perimetry, at a luminance level of 10(3) asb. Falsification of sensitivity gradients and underestimates of depths of scotomata due to stray light effects may be an ever present danger in perimetric determinations. The useful dynamic range in perimetry appears to be limited by photon noise and noise in the neurovisual system on the one hand and by stray light interference on the other.

Adult↗
PubMed1980

[Degenerative and regenerative phenomena in pigmented rabbit irides following irradiation with the xenon arc lamp at different pulse energies (author's transl)].

The morphological condition of the pigmented rabbit iris following irradiation with a Xenon arclamp at four different pulse energies was analyzed. It was shown that: 1. There is a direct relationship between the applied pulse energy and the extent, as well as the rate, of secondary-degenerative transformations. 2. Secondary-degenerative and repair processes occur simultaneously. 3. As opposed to the primary damage event, secondary degeneration appears to progress from the back to the front of the iris. 4. As a rule, pulse energies of less than 1 Joule do not lead to secondary perforation of the iris. Fifteen weeks, after the damage event, regeneration of connective tissue and the larger blood vessels, as well as of myelinated and unmyelinated nerves may be found. 5. The inducing factors, as well as those sustaining the process of secondary degeneration after irradiation of the rabbit iris with high pulse energies, cannot be explained on the basis of morphological findings alone.

Animals↗
PubMed1980

[Analysis of paracentral scotomata with spatially adaptive computer methods].

Flexible computer programs have been developed which are capable of distinguishing between normal and defective areas in the visual field, in that the computer logic only grossly probes normal areas and concentrates on the abnormal areas. As soon as a defect is discovered, it is analyzed with greater accuracy. In this way, no time is wasted analyzing and confirming normal conditions. At the same time, the system is highly effective in respect of pathologically defective areas of the visual field. The principle is described and illustrated with some clinical examples (paracentral scotomata).

Computers↗