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Frank Krummenauer

Publications and source records attributed to Frank Krummenauer.

51 records · Page 3Linked to original sources
PubMed2002

[Standard designs of epidemiological studies and their characteristics in ophthalmology].

This text gives an overview on standard epidemiological study designs and their main advantages and limitations concerning clinical and economical aspects, of performance. Ophthalmological examples are used to illustrate the design characteristics of cross-sectional, cohort and case control studies. These designs are compared by the fictitious planning of an epidemiological study to assess the prophylactical relevance of intraocular antibiotics against post-cataract endophthalmitis; general practical hints for the designing of epidemiological studies are given.

Antibiotic Prophylaxis↗
PubMed2002

[Health Economical Evaluation of antibiotic prophylaxis against postoperative endophthalmitis].

BACKGROUND: Two independent epidemiological studies recently suggested the prophylactic relevance of an intraocular antibiosis against endophthalmitis after cataract surgery. The resulting intervention programme, however, has not only ethical drawbacks, but also has a health economical dimension, which will be focussed in this paper. MATERIAL AND METHODS: A cost analysis is performed to compare the direct costs saved by prevention of endophthalmitis cases and the costs generated by the prophylaxis itself. Furthermore, the clinics' indirect costs due to treatment of unprevented endophthalmitis cases are estimated. RESULTS: The overall gain in direct costs turns out to be about 368 000 Euro p. a., the indirect costs from the clinics' view can be reduced by about 260 000 Euro p. a. due to prevention of endophthalmitis cases by the antibiotic intervention. CONCLUSIONS: From an economical point of view, antibiotic prophylaxis can be suggested; the risk of longitudinally reduced antibiotic effectiveness of the antibiotic agents, however, strongly calls for an overall health political decision rather than for an immediate implementation of the corresponding intervention programme.

Antibiotic Prophylaxis↗
PubMed2002

[I: Box whisker plots--Flexible alternative to "MSE Plots"].

Data description for continuous parameters is sometimes only based on means and standard deviations of measurement series, graphical representation only concentrates on corresponding "MSE plots", which provide means and standard deviations or even only mean squared errors. However, this strategy is only correct for normally distributed data. Outliers may seriously bias mean and standard deviations and may therefore lead to wrong clinical conclusions. The present paper suggests the use of medians and quartiles, which - just like their graphical pendant, the nonparametric "box whisker plot" - can be applied much more flexibly.

Bias↗
PubMed2002

[II: Difference plots or scattergram--when to use which?].

Sometimes the statistical comparison of diagnostic measurement methods or subsequent measurement series in the same individuals is based on bivariate scattergrams; correlation coefficients and linear regression lines are provided in addition. However, this strategy for data representation must be considered inappropriate, as soon as the measurement series under consideration show the same physical index (e.g. repeated measurement of the intraocular pressure [mm Hg] 2 and 4 weeks after glaucoma surgery). Such data can be handled by computation of the intraindividual difference of an individual's measurement. The resulting series of intraindividual deviations can then be analysed using standard strategies: description can be based on the intraindividual differences' median and quartiles, graphical representation on the differences' distribution's box whisker plot. This procedure is particularly attractive for data arising from ophthalmological studies, when two eyes of one patient are to be compared. The statistical comparison of diagnostic methods can further be based on the Bland/Altman diagram, which not only illustrates the distribution of differences, but also motivates a dependence between the order of deviations and the absolute order of the measurement values. Whereas a box plot of intraindividual differences and a Bland/Altman diagram illustrate the concordance of two measurement series, the correlation scattergram rather visualizes their reproducibility.

Computer Graphics↗
PubMed2002

[III: "Relative Risk" and "NNT"--Descriptive Measures for Binary Data].

Description of categorial data can often be based on contingency tables. However, percentages appearing in such tables must be meaningful: For most applications, it may be useful to employ factors of causal influence as the row entry variable and relate percentages to sub-groups defined by these row entries ("row percentages"). The comparison of success frequencies (i. e. binary information on "therapy success yes/no") may be based on two therapies, respective success frequencies and their ratio, the relative risk. In addition the success frequencies' difference, the absolute (or excess) risk, can be transformed into the "number needed to treat" (NNT). Many international journals demand this surrogate measure for the short summary of clinical and epidemiological trial reports, since it allows a direct comparison of the results at hand with the results of previous trials. If, for example, prophylactic vaccination strategies are evaluated, the relative risk estimates the order of risk reduction by vaccination, whereas the NNT estimates the number of patients needed to treat or vaccination needed to apply to avoid disease occurrence.

Bias↗
PubMed2002

[IV: Significance tests -- when to apply which one?].

Standard statistics software packages offer a variety of significance tests. The major problem, however, is the correct choice of an appropriate significance test for the underlying data and design setting. In general, the choice of significance tests should decide between two sample versus one sample (i.e. interindividual versus intraindividual) analyses; a further determinant is the clinical endpoint's scale level (mainly continuous or categorical). Two sample comparisons can be performed using the Wilcoxon test for continuous endpoints and the exact Fisher test for binary endpoints. Intraindividual comparisons become feasible using the sign test for continuous and the McNemar test for binary endpoints. Time to event data can be analysed using the log rank test. If one measurement series has to be compared to a single reference value, the sign test can be applied for continuous data, the binomial test for binary data.

Data Interpretation, Statistical↗
PubMed2002

[V: p values: what they do tell and what they don't...].

Both an extensive data description and an explicit assessment of a study result's statistical significance should be presented in the result section of a clinical trial report. Whereas the description illustrates the order and clinical relevance of the study findings, the statistical significance describes its generalizability to patients not included in the clinical trial: Despite the random recruitment of patients into a trial, the study results may fail to represent clinical reality (for example the trial might show falsely positive efficacy findings, whereas in "clinical reality" efficacy appears rather limited). A p value measures the statistical significance of a study result -- the smaller the p value turns out, the fewer statistical evidence for "random" findings. The clinical relevance of study findings can be measured by median differences or absolute and relative risks, for example, between two therapeutic strategies. Compact table structures for the simultaneous representation of clinical relevance and statistical significance in a paper's result and discussion section are proposed.

Clinical Trials as Topic↗
PubMed2002

[Retrobulbar irradiation for Graves' ophthalmopathy -- long-term results].

BACKGROUND: Significance of retrobulbar irradiation in patients suffering form Graves' ophthalmopathy, though established since almost one century, is subject of scientific debate. The present study investigated the effect of retrobulbar irradiation using a standardized protocol focussing on long term results. PATIENTS AND METHODS: Between 1981 and 1997, 104 patients treated by retrobulbar irradiation (10 to 20 Gray) due to Graves' disease. Twenty-nine of these underwent irradiation as sole treatment (mean follow-up 57 months), while in the remaining 75, it was combined with a systemic steroid treatment (mean follow-up 40 months). Patients were evaluated regarding proptosis, intraocular pressure, lid signs, motility as well as subjective assessment of double vision and retrobulbar pain. RESULTS: While proptosis remained unchanged, lid signs, chemosis and intraocular pressure showed slight and statistically significant improvement. However, these findings were considered to be clinically insignificant. Retrobulbar pain was improved in 75 % of patients. 25 % of patients showed improved motility, 75 % remained stable, and in none of them was there a deterioration of ductions. Results proved stable even in long-term follow-up. 25 % per cent of patients underwent a surgical procedure one year after radiotherapy. CONCLUSIONS: In our series, we could not demonstrate an additional benefit of systemic steroids when combined with retrobulbar irradiation. Up to sixteen years after treatment, no treatment-related adverse reaction was seen. We found a remarkable improvement in ocular motility. This holds even more true in comparison to the natural course of the condition. Retrobulbar irradiation seems to shorten the duration of the disease, thus allowing earlier performance of eventual rehabilitative surgery.

Adult↗
PubMed2002

Blood flow velocity waveforms of the fetal middle cerebral artery in a normal population: reference values from 18 weeks to 42 weeks of gestation.

The aim of this prospective cross-sectional study was to establish new Doppler reference curves for peak blood flow velocities (Vmax, Vmean, Vmin) and impedance indices (PI, RI) of the middle cerebral artery at 18-42 weeks of gestation by an automatic wave form analysis integrated into the ultrasound device. In 962 low-risk pregnancies, blood flow velocities were derived from the middle cerebral artery with pulsed color Doppler ultrasonography. Reference curves were constructed for the individual parameters based on a growth function from a four-parameter class of monotonic continuous functions according to the smallest square principle for maximum blood flow velocities, as well as on a polynomial function for resistance indices. Further assessed was intra-observer reliability. The results obtained for maximum blood flow velocities demonstrate a continuous increase (Vmax = 26.8 cm/s to 59.1 cm/s, Vmean = 11.2 cm/s to 29.7 cm/s and Vmin = 4.9 to 15.8 cm/s) over the period from 18 to 42 weeks of gestation. In contrast, reference curves for the pulsatility and the resistance index are characterized by a parabolic pattern (18 weeks: 1.5; 28 weeks: 1.9; 42 weeks: 1.1 and 18 weeks: 0.68; 28 weeks 0.8; 42 weeks: 0.61). Intraobserver reliability for PI, RI, Vmax, Vmean, and Vmax were 87%, 83%, 80%, 83% and 93%, respectively. At constant measurement conditions, the reference ranges for blood flow velocities and impedance indices in the middle cerebral artery established by this study were found to be a useful non-invasive tool in risk assessment for fetal anemia, as well as in the Doppler ultrasound observation of the course in fetuses with intrauterine growth restriction.

Adult↗
PubMedDate not supplied

[VI: Confidence intervals--an alternative for p values].

Confidence intervals combine the ideas of clinical relevance and statistical significance by using one instructive expression, which enables remarkable reduction of table structures and result sections in scientific publications. Confidence interval based conclusions can be transferred from a clinical trial to its underlying study population with respect to a residual statistical error probability, i.e. the significance concept is retained. However, their presentation using the original unit of the clinical endpoint under consideration allows for immediate interpretation of the results' clinical impact. For example, the comparison of two therapy groups based on a binary endpoint becomes feasible using the relative risk's confidence interval. If "1" is not contained in the interval, the therapy groups significantly differ concerning this endpoint. The larger the interval turns out, the less precise the characterisation of the "real" risk value based on the study risk estimate. The larger the risk estimate turns out, the more clinical relevance.

Antibiotic Prophylaxis↗
PubMedDate not supplied

Is homelessness a risk factor for eye disease? Results of a German screening study.

BACKGROUND: There is general agreement on the presence of a correlation between poverty and impaired health. However, only scarce data are available on whether this also applies to the incidence of eye disease. The present study was carried out to evaluate the prevalence of ocular disease in homeless people in Germany. METHODS: 107 homeless people (97 male, 10 female; mean age 49 years, range 18-81 years) treated in specialised social service institutions were investigated prospectively according to a standardised ophthalmological screening protocol. This comprised visual acuity, assessment of pupillary light reaction, intra-ocular pressure, slit lamp examination as well as funduscopy. RESULTS: The median best-corrected visual acuity of all 213 eyes examined was 0.8 (range: no light perception to 1.25). 74 eyes of a subgroup of 50 patients showed one or more of the following disorders: 32% of the patients suffered from external eye disease, 8% exhibited a cataract associated with a visual acuity of 0.63 or below. 6% of the patients had optic nerve atrophy, and 4% suffered from amblyopia. Diabetic retinopathy as well as age-related macular degeneration were detected in 2%, while anophthalmos, lid malposition and traumatic choroidal rupture were noted in 1% of patients. The median visual acuity measured in these 74 eyes was 0.5 (range: no light perception to 1.25), which differs significantly from the acuity of 0.8 in the entire study population (p < 0.001). The prevalence of legal blindness according to WHO criteria was 2%. CONCLUSIONS: The present study revealed an unexpectedly high prevalence of optic nerve atrophy in homeless people. The prevalence for cataract and legal blindness was slightly higher than in representative epidemiological investigations. Thus, homelessness seems to be correlated with an increased ocular morbidity. As best-corrected visual acuity differed significantly between eyes with and those without eye disease, the assessment of this parameter may serve as a cost-effective first-stage screening method.

Adolescent↗
PubMedDate not supplied

Graphic representation of data resulting from measurement comparison trials in cataract and refractive surgery.

BACKGROUND AND OBJECTIVES: The evaluation of new diagnostic measurement devices allows intraindividual comparison with an established standard method. However, reports in journal articles often omit the adequate incorporation of the intraindividual design into the graphic representation. PATIENTS AND METHODS: This article illustrates the drawbacks and the possible erroneous conclusions caused by this misleading practice in terms of recent method comparison data resulting from axial length measurement in 220 consecutive patients by both applanation ultrasound and partial coherence interferometry. RESULTS: Graphic representation of such method comparison data should be based on boxplots for intraindividual differences or on Bland-Altman plots. Otherwise, severe deviations between the measurement devices could be erroneously ignored and false-positive conclusions on the concordance of the instruments could result. CONCLUSION: Graphic representation of method comparison data should sensitively incorporate the underlying study design for intraindividual comparison.

Cataract↗
PubMedDate not supplied

Clinical report with up to 4 years of follow-up on a cervically modified stepped screw-type implant.

PURPOSE: In 1998, a modification of the macrostructure of the Frialit-2 implant in the cervical region was introduced to stabilize peri-implant bone. Limited data are available on the clinical effect of this modification. Therefore, the soft-tissue situation, marginal bone loss, and implant failure rate were analyzed after 4 years of clinical experience with the modified Frialit-2 Synchro implant. MATERIALS AND METHODS: From 1998 to 2001, 190 cervically modified implants were placed and documented prospectively in 58 patients. Of these implants, 147 were placed in original jaw bone, 22 in areas augmented with local osteoplasty, and 21 in iliac crest bone graft. The main indications for implantation were an atrophic edentulous alveolar crest (n = 99) and support for a partial denture (n = 39), followed by restoration of a shortened dental arch (n = 28) and single tooth replacement (n = 24). In a special clinical examination, 39 patients with 134 implants were investigated. RESULTS: The average in situ time of the 134 implants was 23.1 months. Failing osseointegration (n = 10), peri-implantitis (n = 1), and tumor resection (n = 3) in 8 patients resulted in the failure of 14 of 190 implants (7.4%). One patient with 4 implants died (2.1%). Currently, 3 patients with a total of 6 implants have been lost to follow-up (3.1%), and 166 implants remain in situ (87.4% of 190). DISCUSSION: Using different implant success criteria, success rates of 88.8% and 82.8% were calculated. CONCLUSION: Based on the results, the Frialit-2 Synchro implant appears to be a useful implant system for the indications analyzed.

Alveolar Bone Loss↗