Search PubMed⌕ Search

Biomedical subjects

F Fankhauser

Publications and source records attributed to F Fankhauser.

At least 73 records · Page 4Linked to original sources
PubMed1991

A comparison of unweighted and fluctuation-weighted indices (within the central 28 degrees of glaucomatous visual fields measured with the Octopus automated perimeter).

The main visual field indices of Flammer and the analogous ones of Heijl have been compared based on a population of 113 glaucomatous visual fields. It is shown that for the population studied, the differences between the two sets of indices are negligible for Octopus G1 program results and that they may thus be used interchangeably.

Glaucoma↗
PubMed1991

The effects of weighting the "mean defect" visual field index according to threshold variability in the central and midperipheral visual field.

Two visual field indices, the mean defect (MD) of Flammer and the mean deviation (MD) of Heijl, have found wide acceptance among perimetrists. We compared these indices in 169 visual fields from normal- and high-tension glaucomatous eyes. Visual field damage in these eyes varied from slight to severe. In computations of the mean deviation index, the threshold values are weighted by the threshold deviations obtained from normal eyes as a function of eccentricity. However, the present study shows that the differences between the two indices in the population studied are negligible. Thus, subsequent interpretation is not affected by the choice of index, and the two MD indices may be considered to be interchangeable for the types of visual fields used in this study and for program-G1 examinations carried out using Octopus automated perimeters. Since we found smaller increases in local intersubjective fluctuations as a function of eccentricity in 274 normal visual fields as compared with results published by others, caution is indicated for interpretation of the visual field using probability weighting.

Humans↗
PubMed1990

Evaluating a perimetric expert system: experience with Octosmart.

When evaluating expert systems to be used in clinical perimetry, various aspects of their performance as compared with that of human interpreters must be considered. In this investigation, the results produced by the new Octosmart diagnostic program have been compared with the performance of three interpreters with various amounts of experience in visual field analysis. The evaluations were based on 27 visual fields with glaucomatous damage, which had been examined with the Octopus program G1. It is shown that in borderline cases (i.e., neither clearly normal nor clearly pathological) where strict statistical criteria must be employed in order to distinguish between possible pathology and artifacts, the "personal styles" of human interpreters, more than standardized decision criteria, implicitly guide the decision process, resulting in unpredictable, non-standardized interindividual differences. A standardized expert system, based on constant, explicit, and logical criteria is therefore considered to be superior to unaided human interpretation. It is pointed out that the influence of the implicit decision criteria of human interpreters must be controlled carefully if expert systems are to be evaluated with reference to human interpreters.

Analysis of Variance↗
PubMed1990

[Bruch's membrane and its significance for retinopexy following laser irradiation].

Retinopexy may be produced by either of two mechanisms following transpupillary irradiation of the retina with the Nd:YAG laser. Which of these mechanisms is operative will depend on the degree of disruption produced within the elastic component of Bruch's membrane. Small defects in the elastic component of Bruch's membrane are soon completely bridged by regenerated retinal pigment epithelium (RPE) cells. However, there is a risk of subretinal neovascularization in such defects. Large defects in the elastic component of Bruch's membrane are not completely bridged by regenerating RPE cells before proliferating Müller cells invade this region and spread from it, mushroom-like, within the choroid. In this case subretinal neovascularization does not occur. In the former instance (small defects) retinopexy is achieved by a process of interdigitation between the microvilli of Müller and RPE cells; and in the latter (large defects) via a press-stud-like anchorage of Müller cells within the choroid. It has not yet been established whether these two retinopexy phenomena, observed after irradiation of rabbit retinas, occur in the same way in man.

Animals↗
PubMed1990

Evaluating human and automated interpretation of visual field data in perimetry.

The complexity of visual field result evaluation has increased with the advent of automated perimetry. This in turn makes software assistance such as provided by the new Octosmart program interesting and desirable. Its accuracy and reliability in visual field evaluation must be tested, though, and the testing methodology itself must be developed. For this purpose, 27 visual fields were evaluated by three human interpreters and the Octosmart program. Based on a newly developed compound index, the performance of the three interpreters and Octosmart is described and a high degree of consistency is demonstrated.

Diagnosis, Computer-Assisted↗
PubMed1990

Transpupillary irradiation of the rabbit retina with the cw-Nd:YAG laser. I. Acute morphologic effects produced using two different pulse forms.

The retinas of six pigmented rabbits (12 eyes) were irradiated with a cw-Nd:YAG laser using two different pulse forms, in conjunction with a constant pulse duration of 200 msec and a retinal focus diameter of 200 microns. The first pulse form (a) was characterized by an initial transient, lasting 15-20 msec, with a peak power twice that of the ensuing plateau phase of 180-185 msec. The second pulse form (b) was almost rectangular in shape. Although the average energies (and powers) for each pulse form were identical, almost 20% of this entity was delivered within the first 20 msec for the first pulse form. Impact lesions were examined at the biomicroscopic, light, and electron microscopic levels, and the characteristic morphologic features described for the cw-mode in general. Comparison of the effects produced using each pulse form revealed a number of differences. At low pulse energies (less than 150 mJ) the rectangular pulse form produced a photocoagulation reaction within the outer sensory retina, but when using the pulse form with the initial transient, this effect was superimposed by a degree of mechanical disruption. Ruptures produced within the elastic component of Bruch's membrane first appeared at lower pulse energies (ie, at 75 mJ, as opposed to 150 mJ for the rectangular pulse form) and were more frequent, and choroidal macrohemorrhaging (observed at pulse energies greater than or equal to 200 mJ) occurred only, when this latter pulse form was employed. Each of these phenomena may be attributed to the higher power and energy densities attained during the initial transient, which has disruptive properties. In order to avoid the risk of severe bleeding, these irradiation parameters should be maintained below approximately 6.4 X 10(3) W/cm2 and approximately 0.13 X 10(3) J/cm2.

Animals↗
PubMed1990

A new universal laser apparatus for intra and extraocular irradiation tasks in the eye.

We describe a universal laser apparatus for multipurpose clinical tasks. The main unit consists essentially of a Haag-Streit slit lamp combined with a rigidly mounted Q-switched laser. The apparatus is designed basically for performing photodisruptive tasks. Radiation emitted by either a pseudocontinuous cw Nd:YAG laser (with a dynamic range of 10 W) or by an air-cooled 4-W argon ion laser energy source either may be transmitted via fiber optics into the main unit or, when detached from the main unit, may be used independently. Energy emitted by the modules and transported by specialized light cables and delivery systems can be used to perform transscleral Nd:YAG laser irradiation of the ciliary body or the choroid and retina. Probes are available for endocoagulation of the latter two by either cw Nd:YAG or argon laser light. Other probes are being developed for chorioretinotomy, internal sclerostomy, dissection of the sclera, or for other extrabulbar work. All functions are monitored and displayed by a central processor.

Anterior Eye Segment↗
PubMed1989

Puptrak 1.0--a new semiautomated system for pupillometry with the Octopus perimeter: a preliminary report.

A provisional, semiautomated version of a system for automated testing of the afferent pupillary reflex with perimetric methods under controlled conditions is described. The target projected onto the perimeter cupola is used as the stimulus for triggering the pupillary response. In a modification to the Octopus 201, the pupil is illuminated by two IR LED diodes, while the pupillary responses are recorded by the onboard IR sensitive TV camera built into the perimetric unit. Measurements of the pupillary area as a function of time and stimulus luminance have been performed and have resulted in consistent results. Here, one perimetric program, working with stimuli above the threshold for the afferent pupillary light reflex is described. The present setup works with system-specific software and standard hardware, the central data processing unit being a desk-top computer (IBM PC AT-03). The mating of an automated pupillary measuring unit to an automated perimeter may open the door for a more widespread evaluation of the value and the clinical application range of pupillary perimetry and may be of interest in other areas of visual and clinical psychophysics. The shortcomings of the present system, in particular insufficient temporal resolution and lack of full automation, are being removed at the present time.

Computer Systems↗
PubMed1989

The mechanism of aqueous outflow following trabeculectomy. A light and electron microscopic study.

The morphological effects of trabeculectomy, performed as therapy for a case of chronic simple glaucoma, are described in the two eyes of a patient ten and thirteen months after treatment. Ten months after surgery, a transscleral channel, extending from the position formerly occupied by Schlemm's canal to the conjunctiva, is found. This channel is formed from a network of extended fibroblasts and loosely-packed collagenous tissue, and a large number of vessels, including both dilated blood capillaries and lymphatic vessels, develop within it. The sclera and subconjunctiva react differently to the presence of the nylon sutures. The findings support the hypothesis that the formation of an intrascleral outflow route stimulated by surgical intervention plays an important role in lowering IOP after trabeculectomy.

Aged↗
PubMed1989

Cyclophotocoagulation in glaucoma therapy.

In a morphological study, the long-term effects of transscleral cyclophotocoagulation on rabbits using the free-running Nd:YAG laser with either a contact or a non-contact delivery system are described. A marked atrophy of the irradiated ciliary processes may be observed. Regeneration of the ciliary epithelial layers is incomplete at least up to 8 months after treatment. The vascular network is also atrophic, and shows a small regenerative capacity only.

Animals↗
PubMed1989

The effect of transscleral laser cyclophotocoagulation on rabbit ciliary body vascularization.

Long-term changes in the vascular network of rabbit ciliary processes induced by Nd:YAG laser cyclophotocoagulation were examined both from a morphological viewpoint and with respect to three-dimensional organization (in vascular casts). Relative changes in intraocular pressure (IOP), monitored within eyes irradiated across one-quarter, one-half, three-quarters, or all of the ciliary body circumference, are discussed in relation to morphological changes. The clinical implications of these findings are considered.

Animals↗
PubMed1989

Integrated optical fiber systems--some theoretical aspects.

The specific advantages of a number of integrated optical systems, consisting of optical probes of various shapes and materials, coupled to a number of optical fibers are described. The radiation fields of the various systems vary significantly in their performance and the clinical effects may be expected to vary correspondingly. This is a step forward in the theoretical evaluation of optimal laser microsurgical tools for specific applications.

Aluminum Oxide↗