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Biomedical subjects

A Jenni

Publications and source records attributed to A Jenni.

11 recordsLinked to original sources
PubMed2003

Quantitative microstructure analysis of polymer-modified mortars.

Digital light, fluorescence and electron microscopy in combination with wavelength-dispersive spectroscopy were used to visualize individual polymers, air voids, cement phases and filler minerals in a polymer-modified cementitious tile adhesive. In order to investigate the evolution and processes involved in formation of the mortar microstructure, quantifications of the phase distribution in the mortar were performed including phase-specific imaging and digital image analysis. The required sample preparation techniques and imaging related topics are discussed. As a form of case study, the different techniques were applied to obtain a quantitative characterization of a specific mortar mixture. The results indicate that the mortar fractionates during different stages ranging from the early fresh mortar until the final hardened mortar stage. This induces process-dependent enrichments of the phases at specific locations in the mortar. The approach presented provides important information for a comprehensive understanding of the functionality of polymer-modified mortars.

Adhesives↗
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

A comparison of cupola-free perimetry with conventional perimetry: preliminary results.

In the comparison of ten normal and two pathological visual fields, excellent agreement was found between examinations made with Octopus perimeters (types 201 and 500) and a prototype version of a new cupola-free perimeter (CFPP). The examination of a single glaucomatous visual field, however, exhibited an elevated mean defect value with the prototype instrument in comparison with Octopus 201 examinations of the same visual field. Although this difference may be easily explained by long-term fluctuation effects, further investigations based on a broader empirical basis will be required. Based on the results of this preliminary work the following remarks can be made with respect to the cupola-free perimeter: provided that the zero point of the dB scale is chosen appropriately, ie, with a stimulus luminance of about 4,000 asb used as the 0 dB level, the same differential light sensitivity (DLS) values for normal visual fields can be obtained with the CFPP as with all Octopus models (201, 500, 2000). Within the limits of measurement error, the same decrease of DLS was found with the CFPP as obtained using the other perimeters for test locations (of the G1 program), ranging from the center out to an eccentricity of 30 degrees. Thus it appears that the normal values as used in the other Octopus perimeters can also be utilized in this cupola-free instrument within this range.

Adult↗
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↗
PubMed1988

Extrapolating global visual field indices from local parameters in the nasal region.

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.

Glaucoma↗
PubMed1983

JO and STATJO: programs for investigating the visual field with the Octopus automatic perimeter.

In evaluating the effectiveness of glaucoma therapy the visual field is the most important consideration. Comparison of visual fields is difficult, however, and only large changes are detectable with the methods of manual perimetry currently used. Two programs created for use with the Octopus automatic perimeter are described in this paper. One of the programs, called JO, is sensitive to small changes in threshold; the other, called STATJO, calculates means and converts the results to a form suitable for statistical evaluation.

Computers↗
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↗
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↗