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Biomedical subjects

F Fankhauser

Publications and source records attributed to F Fankhauser.

At least 109 records · Page 6Linked to original sources
PubMed1986

Morphologic findings in the rabbit retina following irradiation with the free-running neodymium-YAG laser. Disruption of Bruch's membrane and its effect on the scarring process in the retina and choroid.

The scarring process induced within the retina and choroid of pigmented rabbits' eyes following irradiation with the neodymium-YAG laser (working in the free-running mode) was examined at the ultrastructural level. Scarring of the sensory retina proceeded rapidly and was well advanced two weeks after irradiation, whereas in the choroid, signs of repair were apparent only after six weeks. This difference in the rate of repair between the two tissues has a bearing on the scarring pattern in the retinochoroid as a whole. The severity of damage to the elastic component of Bruch's membrane also has important consequences in relation to the repair processes in the retina and choroid. Microfractures within this layer, while enabling migrating cells of various kinds to penetrate into the inner collagenous zone, did not prevent complete regeneration of the retinal pigment epithelium (RPE). In instances of greater rupture, however, RPE regeneration was found to stop at the border of the break, and the discontinuity produced within Bruch's membrane and the RPE allowed the glial scar to expand into the choroid. In this region, new formation of vessels was not found.

Animals↗
PubMed1986

Advantages and limitations of the spatially adaptive program SAPRO in clinical perimetry.

The SAPRO program devised for the OCTOPUS 201 automated perimeter, consists of a number of program components. It is designed to be used on the Octopus 201 computer. In its measurement mode, it employs an algorithm which achieves high speed and efficiency. This is made possible by a threshold bracketing strategy which is simpler than the normal OCTOPUS bracketing. Moreover, three grids with test location distributions of increasing resolution are superimposed in succession on the whole or on part of the visual field to be analyzed. Out of the distribution of test locations, only those which fulfill a number of criteria are actually utilized. These criteria must be given and are adaptable to any given clinical problem. As a result, despite the high spatial resolution achieved, only a fraction of the test locations are utilized using SAPRO as compared with a program using a fixed pattern of test locations. The algorithm is thus able to imitate human intelligence, which tends to concentrate stimuli at places which appear to be relevant for the solution of a problem. The results of program SAPRO are disturbed by short- and long-term fluctuations. Their validity is limited, in a manner similar to that encountered in any other threshold determination procedure. A number of printout modes is available which are oriented towards an optimal understanding of the information contained in various examinations. These principles will be illustrated by one case of inactive disseminated chorioretinitis.

Computers↗
PubMed1986

Long-term results of Nd:YAG laser posterior capsulotomy with the Swiss laser.

The Microruptor II (MR-II) Nd:YAG laser developed by Fankhauser was evaluated in a national multicenter prospective study of posterior capsulotomy. Results are reported on 3,711 patients who underwent Nd:YAG laser photodiscission. Ninety-two percent of patients experienced an improvement in vision at some point following photodiscission and the postoperative complications of persistent cystoid macular edema and glaucoma occurred at rates of 2.5% and 0.2%, respectively, indicating the safety and efficacy of the MR-II for posterior capsulotomy.

Adolescent↗
PubMed1986

Thermal effects on the trabecular meshwork induced by laser irradiation: clinical implications deduced from ultrastructural studies on the macaca speciosa monkey.

The pressure lowering effect brought about by irradiating the chamber angle with argon laser light according to Wise and Witter was studied by ultrastructural methods and was analysed in order to ascertain the mechanism responsible. To this end, the effects induced in 4 macaca speciosa monkeys by such irradiation were examined using scanning and transmission electron microscopy. It was noted that the phenomena observed depend critically on the precise location of the irradiation site. When the anterior trabecular meshwork is irradiated, a proliferation of monocellular, atypical corneal endothelium cells occurs which tightly surround the irradiation location. In irradiation of the posterior trabecular meshwork, however, this effect is much less prominent. In both cases, by the end of the twelfth week a progressive, lytic degeneration of the entire trabecular meshwork was observed which reached the inner wall of Schlemm's canal.

Animals↗
PubMed1986

A new contact lens for posterior vitreous photodisruption.

Effective and safe photodisruption requires that the laser pulse be brought to a fine focus. Contact lenses are generally required to compensate for the optical aberrations of the eye which degrade the laser focus. The theoretical analysis of these aberrations has led to the construction of a contact lens which minimizes aberrations in the posterior vitreous. Clinical applications confirm the increased efficacy and safety of posterior vitreous photodisruption using this contact lens.

Contact Lenses↗
PubMed1986

Aiming accuracy in ophthalmic laser microsurgery.

A number of aiming/focusing systems, oriented toward guiding the treatment beams of photodisruptive, high power Nd:YAG lasers, are analyzed and evaluated. A system, consisting of two frequency modulated, rotating laser beams, which outline the Nd:YAG laser beam shape, is shown to be the optimal solution.

Humans↗
PubMed1986

Evaluating the applications of the spatially adaptive program (SAPRO) in clinical perimetry: Part I.

Some clinical application possibilities of a spatially adaptive program (SAPRO) are presented and analyzed. Due to the ability of the program to adapt operationally to the visual field situation that is encountered, useful clinical findings can be obtained, even in patients with complicated visual field disturbances. The spatially adaptive detection mechanism, as well as a simplified bracketing strategy, make it possible to keep the cost/benefit ratio down. Short- and long-term fluctuations, especially when these are large, may compromise the validity of the examination results or place them in doubt. Their effects can be diminished using data reduction methods (averaging). In cases where averaging cannot be applied, one can nevertheless achieve useful results by the appropriate selection of the perimetric visual fields (or portions thereof) that are measured.

Adult↗
PubMed1986

Transscleral cyclophotocoagulation using a neodymium YAG laser.

The effects of a neodymium: YAG laser, working in the free-running mode (1 and 20 millisecond pulses), upon the ciliary body via the transscleral route have been studied using 16 autopsy eyes. The experiments described were designed to find an efficient strategy of transscleral cyclodestruction of the ciliary body. It was found that pulse energies of between 6 and 7 Joules, an exposure duration of 20 milliseconds, and maximal defocusing are optimal. A beam, tangentially oriented and positioned 1/2 to 1 mm posterior to the limbus has a high probability of hitting the ciliary body and damaging the ciliary processes. In these experiments a first generation of contact lenses could not be demonstrated to have an advantageous effect.

Ciliary Body↗
PubMed1985

Choroidal reaction and vascular repair after chorioretinal photocoagulation with the free-running neodymium-YAG laser.

The morphologic effects of the neodymium-YAG laser working in the free-running mode on the choroid of pigmented rabbit eyes have been studied by electron microscopy. Two different mechanisms closing the choroidal vessels were found. The larger vessels of the vascular lamina were closed by platelet aggregation, while within the choriocapillaries a network of fibrin could be observed. The endothelial cells of the vessels were found to be damaged in capillaries as well as in the larger vessels. Within the irradiated area, a revascularization process takes place, expanding from the border towards the center. The process begins a few days after treatment and continues for more than four months. The process of neovascularization is described in detail. Beside fibroblasts, cells could be found that were active in producing elastic fibers.

Animals↗
PubMed1985

Vitreolysis with the Q-switched laser.

We present an overview concerning the current status of photodisruptive methods used in the treatment of pathologic changes in the vitreous space. In one series of 320 cases studied, 65% of the planned dissections of pathologic structures were successful. In a second series of 34 more complicated cases, the success rate was even lower. Complications included 15 retinochoroidal hemorrhages and one damaged posterior lens capsule. When one compares optical-surgical methods with conventional methods, it is obvious that the former aim at achieving goals that are less ambitious than those of classic vitrectomy and, in many cases, serve only to prepare for - and facilitate - a classic vitrectomy. By definition, laser vitreolysis dissects, but cannot remove, the fragments of disrupted structures from the eyeball. However, despite the obvious risks, photodisruptive laser surgery is considered less dangerous than is classic vitrectomy because photodisruption is a "noninvasive" procedure. Since laser vitreolysis is able to solve a number of clinical problems, obviating the need for vitrectomy, the former procedure should receive increasing attention for the treatment of pathologic problems in the vitreous cavity.

Adult↗
PubMed1985

Irradiation of the posterior ocular segment with the neodymium-YAG laser in its free-running mode.

A neodymium-YAG laser, operating in its free-running mode with pulse durations of 10 to 20 ms, was used to treat 63 cases of choroidal and retinal diseases. These cases included diabetic background retinopathies, thrombosis of the central retinal vein or branch retinal vein, neovascular membranes under the pigment epithelium, and retinal breaks or degenerations of the peripheral retina. Because the number of diabetic retinopathies (24) and their average follow-up time (25.5 months) are insufficient for the evaluation of irradiation effects, no definite statement as to the merits of this energy modality in such cases can be made. The irradiation of infarcted retina was followed by extensive atrophy of the involved area. No secondary glaucoma was observed during a follow-up period of 16.4 months. The irradiation in four cases of neovascular subretinal membranes was followed by disappearance of the membranes. However, relapse later occurred in all four cases. The irradiation of eight retinal breaks resulted in solid scar tissue. Two choroidal melanomas were destroyed and did not recur during a follow-up period of 22 months.

Choroid↗
PubMed1985

Neodymium Q-switched YAG laser lysis of iris lens synechiae.

The feasibility of Q-switched Nd: YAG synechiolysis in phakic patients without visible damage to the lens has been demonstrated. The value of this procedure in the management of glaucoma and its advantages over argon laser photomydriasis is discussed.

Aged↗
PubMed1984

Differential light threshold in automated static perimetry. Factors influencing short-term fluctuation.

The scatter of the differential light threshold observed during a single visual field test is called the short-term fluctuation. A number of factors that may influence the magnitude of the short-term fluctuation were studied. The main factor was the level of the differential light sensitivity itself, followed by the rate of false responses in the catch trials. The pupil size was only notable in patients with glaucoma, while age as well as the mean reaction time did not appear to be notable. The short-term fluctuation is not dependent on the location in the visual field up to 27 degrees of eccentricity degrees tested in normal subjects and patients suspected of having glaucoma, but there is a slight tendency in patients with glaucoma for a larger short-term fluctuation in the upper half of the visual field.

Differential Threshold↗
PubMed1984

Ultrastructural changes of the trabecular meshwork of the monkey (Macaca speciosa) following irradiation with argon laser light.

An attempt to elucidate the mechanism of the pressure-lowering effect after treatment of the chamber angle according to Wise and Witter with argon laser light is presented. The ultrastructural effects upon the trabecular meshwork of four Macaca speciosa monkeys were analyzed at planned intervals by scanning and transmission electron microscopy. The ultrastructural effects of the treatment are strongly dependent on the site of the laser burns. Whereas burns delivered to the anterior part of the meshwork are tightly sealed by a monocellular layer of atypical corneoendothelial cells, this mechanism is less marked when delivered more posteriorly.

Animals↗