Biomedical subjects
Publications and source records attributed to F Fankhauser.
The optical performance of a new contact lens for observation and irradiation of the retina and choroid represents a compromise between Goldmann's contact lens and a wide-angle system in regard to magnification, resolution, and size of the field of view.
The local mean and the average difference of four pairs of test locations within the 26 degrees visual field, situated above and below the horizontal nasal meridian, were used to predict the global field indices MD and CLV of the Gl glaucoma program. Out of 539 examinations (194 eyes suspected of having glaucoma), the local indices NDIFF (describing asymmetrical behavior around the nasal horizontal meridian), ND0 (the mean defect in the nasal region), and the global indices MD and CLV were calculated. Seven hundred fifty-five examinations (446 normal eyes) served as a control group. First and second examinations of 146 glaucoma suspect eyes were used to calculate the retest reliability scores for the indices in question. When analyzing the glaucoma suspects, the local index NDIFF, together with the local mean defect, ND0, yielded highly reliable estimates of the global indices MD and CLV, with a retest correlation r = 0.86 for NDIFF, and r = 0.96 for ND0. The covariance of NDIFF with CLV was r = 0.67, while the co-variance of MD with ND0 was r = 0.95. The ranges of the local indices ND0 and NDIFF were each classified into 'normal range' and 'range of suspected pathology', in analogy to the normal and pathological ranges of the global field indices. Equivalence of the local indices with the corresponding ranges of MD and CLV was investigated and the results are shown. The establishment of local indices may prove to be a powerful tool in early detection of glaucomatous damage.
Difficulties encountered when measuring the differential light sensitivity of the blind spot and its surroundings and the clinical interest of such measurements are reported. The determination of the differential light sensitivity across step gradients, as well as abrupt changes observed at and close to the blind spot, may pose severe problems, because both are strongly influenced by even slight fixation instability. However, other factors reported herein may be equally important. The insight gained here may be cautiously extrapolated to the difficulties (and to the efforts to overcome them) encountered when measuring other scotomata in the visual field having sensitivity distributions similar to those of the blind spot. The sensitivity distribution in the blind spot and the pericoecal region may be important in a number of disease entities, particularly in glaucoma and neurologic diseases.
The BSPOT evaluation program has been created to run on an IBM-PC type computer. It accepts Octopus SAPRO data that have been transferred to the PC and enables the user to display aspects of the data for evaluation purposes. Some applications are illustrated using the results of two blind spot examination series, one normal and the other pathologic, and the results of an angioscotoma examination. Although the program was designed for the display of blind spot data, any SAPRO examination data may be used.
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The exact mechanism of irradiation-induced occlusion of normal or abnormal retinal vessels is still to a large extent obscure. Blood flow acts as a powerful heat dissipation mechanism. Therefore, a procedure which reduces flow velocity as rapidly as possible after the beginning of irradiation may work with higher efficiency. A theory based on a simplified assumption states that vessel narrowing techniques, which involve only a short length of the vessel to be occluded by a small focus diameter irradiation beam, are less efficient in bringing blood velocity down than a procedure which narrows the vessel over a greater length by a larger focus diameter irradiation beam. The thrombus building up over a greater length of the affected part of the vessel may also better resist the pressure head building up after thrombogenesis is complete because friction between thrombus and vessel wall is larger, and occlusion may, therefore, be more durable. One has to assess, therefore, whether a small-spot technique, which is presumed to be less efficient and may need repetitions, is in fact less innocuous for the surrounding retina--as is generally assumed--than a technique using a larger beam diameter, which, because it is more efficient, may need fewer or even no repetitions.
The long-term tissue response of monkey eyes to trabeculoplasty produced at the chamber angle by neodymium:YAG (Nd:YAG) laser (thermal mode) was investigated. Four weeks after irradiation, a monolayer of corneal-like endothelial cells extended over the trabeculum in impact zones, with partial occlusion of intertrabecular spaces; this condition persisted at all subsequent stages of observation (viz, up to 13 weeks). Both primary and secondary degeneration of trabecular endothelial cells occurred predominantly at the posterior border of the juxtacanalicular tissue, and continued throughout the observation period. Lysis and degradation of collagen fibrils were also prominent in this region, and collagen-phagocytosing cells could be seen at all stages. Although activated fibroblasts were marked in this zone, regeneration processes were, in general, less marked than those of degeneration. The significance of these findings in relation to the mechanism by which trabeculoplasty works is discussed.
The neodymium:YAG laser may be used to advantage in the thermal mode for iridectomy. A variety of other tasks which are traditionally performed using the argon laser can also be efficiently carried out using this mode of operation. In this article the authors describe in particular the method of transscleral cyclophotocoagulation with the neodymium laser in the treatment of glaucoma, which is becoming increasingly popular.
The effects upon the iris of radiation emitted by a Nd:YAG laser working in its thermal (free-running) mode and transmitted through the sclera were studied. The advantages and disadvantages of a fiber optic system, as compared to a conventional optical system, were studied using eight autopsy eyes. It was shown that the conventional optical system as well as a fiber optic system are both able to perforate the iris completely and to blast away or destroy the pigment epithelium. One merit of the fiber optic system as compared to the conventional system is that it requires considerably less energy for the same effect. This is partially because the sclera, when compressed, becomes more transparent and thus transmits a greater amount of laser energy.
We report the morphology of transscleral iridotomies applied to human cadaver eyes using a free-running Nd:YAG laser (pulse duration: 20 ms, pulse energy: 1.5-6 J) with and without a fiber optic system. The pigment epithelium, which represents the barrier to the aqueous humor for passing through the iris, is damaged and blasted away over great areas. The mesothelial layer at the anterior surface of the iris is also broken up by the laser beam. Using low pulse energies, the iris stroma is only partially damaged. The destruction of the iris is caused by generation of heat due to absorption of radiated energy.
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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.
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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.
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.
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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.
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.