Biomedical subjects

Berthold Lausen

Publications and source records attributed to Berthold Lausen.

8 recordsLinked to original sources

PubMed2006

Improving glaucoma diagnosis by the combination of perimetry and HRT measurements.

PURPOSE: The aim of this study was to determine, whether the combination of morphologic data of the optic nerve head and visual field (VF) data would improve diagnosis of glaucoma, on the basis of the measurements alone. PATIENTS AND METHODS: Eighty-eight perimetric glaucomatous and 88 normal optic discs from the Erlangen Glaucoma Registry were matched for age. All normals and patients were examined in a standardized manner (Slitlamp biomicroscopy, gonioscopy, 24 h-applanation tonometry, automated VF testing, 15-degree optic disc stereographs, and Heidelberg Retina Tomograph (HRT)-scanning of the optic disc). The HRT variables were calculated in 4 optic disc sectors. All variables were calculated with the software's standard reference plane. To gain the same allocation of sectors as provided by the HRT software, the VF responses were averaged within 4 sectors. Classification results of these VF responses were compared with the summarized results within 4 sectors. Six different combinations of morphologic and VF data were used to assess their suitability to diagnose the disease. HRT measurements, and the standard output of the Octopus (HRT/PERI1), HRT measurements and the summarized sectors and their standard deviations (HRT/PERI2), HRT measurements, standard output of the octopus and the summarized sectors and their standard deviations (HRT/PERI1/PERI2), standard output of the Octopus (PERI1), summarized sectors of the Octopus and their standard deviations (PERI2) and HRT measurements. To assess the diagnostic value of the different data sets machine learning classifiers, stabilized linear discriminant analysis, classification trees, bagging, and double-bagging were applied. RESULTS: Combination of morphologic and VF data improved the automated classification rules. The accuracy to diagnose glaucoma just by VF and HRT indices was maximized for double-bagging using both diagnostic tools. An estimated misclassification probability of less than 0.07 could be achieved for the primary open angle glaucoma patients combining HRT and VF sectors by double bagging. So highest sensitivity was 95% and specificity 91%, achieved by double-bagging and combination of HRT, PERI1, and PERI2. CONCLUSIONS: The combination of optic disc measurements and VF data could not only improve glaucoma diagnosis in future, but could also help to find an objective way to diagnose glaucomatous optic atrophy. The limitation of the topographic relationship between structure and function is the individual variability of the optic disc morphology and the subjective variability of VF testing.

Female↗

PubMed2005

Microarray versus conventional prediction of lymph node metastasis in colorectal carcinoma.

BACKGROUND: The authors investigated whether microarray-based gene expression analysis of primary tumor biopsy material could be used to predict lymph node status in patients with colorectal carcinoma (CRC). Lymphatic metastasis strongly determines treatment algorithms in CRC. Currently, postoperative histology results are needed to determine lymph node status. Reliable preoperative information would be useful to advance treatment strategies. METHODS: In specimens from 66 patients with CRC from the Erlangen Registry of Colorectal Cancer, 41 shock-frozen samples of International Union Against Cancer (UICC) Stage I-II CRC and 25 samples of UICC Stage III CRC were microdissected manually, RNA was isolated, and gene chips (HG-U133A; Affymetrix) were hybridized. Prediction rates for lymphatic metastasis were calculated using conventional clinicopathologic parameters, gene expression data, and a combination of both. Prediction error, specificity, and sensitivity were analyzed using six different statistical classifiers. RESULTS: Analysis of conventional parameters produced a positive prediction rate that ranged between 53% and 61%, sensitivity of 42%, and specificity of 72%. Microarray prediction rates were between 62% and 67% for lymphatic metastasis. Specificity was between 76% and 83%, and sensitivity was between 38% and 48%, depending on the statistical procedure. The conventional estimates were improved by 9-12% when array data were added. CONCLUSIONS: Current data show that the prediction of lymphatic metastasis can be improved by gene expression profiling of the primary tumor biopsy, alone or in combination with conventional parameters. Gene expression profiling may become valuable increasingly in planning treatment for patients with CRC.

Aged↗

PubMed2004

Diagnostic value of multifocal VEP using cross-validation and noise reduction in glaucoma research.

BACKGROUND: The diagnostic value of multifocal visual evoked potentials (mf VEP) in glaucoma research is still under debate. Several previous studies proclaim it to be a useful tool for clinical applications, but according to other studies, different problems (low specificity, poor records, and interindividual variation) still retard its clinical use. The aim of the present study was to examine whether the mf VEP data obtained with the RETIscan system are appropriate for formulating a classification rule for glaucoma. METHOD: We examined and evaluated 65 eyes in 38 advanced glaucoma patients and 27 normal subjects, using four occipital gold cup electrodes (cross layout) for bipolar recording and a CRT monitor (display diameter 60 degrees, chequerboard pattern reversal, 60 segments in dartboard layout) for stimulation. In each case, eight cumulative measurements (77 s each) were made. The data of the 60 segments were cross-correlated with a RETIscan-internal VEP norm ("VEP finder"), combined in 16 sectors, and evaluated via the classification technique "double-bagging" and the Wilcoxon U-test. RESULTS: In three out of the 16 sectors, the VEP amplitudes of the patients were significantly reduced (Wilcoxon U-test). Applying double-bagging on the cross-correlated data (with VEP finder) resulted in a sensitivity of 75% and a specificity of 71%, and the estimated misclassification rate was 27%. For uncorrelated data (without VEP finder), the same analysis achieved a sensitivity of about 60% and a specificity of 40%. CONCLUSIONS: Estimated sensitivity and specificity suggest that by using the RETIscan system for recording, a classification of the VEP data--i.e. a separation between normal and glaucoma subjects--is possible.

Biomedical Research↗

PubMed2004

Bagging survival trees.

Predicted survival probability functions of censored event free survival are improved by bagging survival trees. We suggest a new method to aggregate survival trees in order to obtain better predictions for breast cancer and lymphoma patients. A set of survival trees based on B bootstrap samples is computed. We define the aggregated Kaplan-Meier curve of a new observation by the Kaplan-Meier curve of all observations identified by the B leaves containing the new observation. The integrated Brier score is used for the evaluation of predictive models. We analyse data of a large trial on node positive breast cancer patients conducted by the German Breast Cancer Study Group and a smaller 'pilot' study on diffuse large B-cell lymphoma, where prognostic factors are derived from microarray expression values. In addition, simulation experiments underline the predictive power of our proposal.

Breast Neoplasms↗

PubMed2003

Results and complications of hydrophobic acrylic vs PMMA posterior chamber lenses in children under 17 years of age.

PURPOSE: To compare results and complications of implantation of hydrophobic acrylic foldable intraocular lenses in children with those of polymethylmethacrylate (PMMA) intraocular lenses. METHODS: In a retrospective study, we analyzed results of cataract surgery with posterior chamber lens implantation in 30 eyes of 30 patients aged 1-16 years. In 10 eyes, acrylic (Alcon AcrySof) intraocular lenses, and in 20 eyes, single-piece PMMA posterior chamber lenses were implanted. Indications for cataract surgery (blunt or penetrating trauma, zonular cataract, cataracta polaris posterior, posterior lenticonus) and mean age at implantation were comparable in the two groups. Mean patient age at surgery was 8.6+/-4.6 years (range 3-16 years) for the acrylic vs 6.3+/-4.3 years (range 1-16 years) for the PMMA group. Mean follow-up was 1.0+/-0.7 years (range 0.1-2.2 years) in the acrylic group and 1.8+/-1.5 years (range 0.1-5.7 years) in the PMMA group. Primary anterior vitrectomy was performed in 7 eyes in the PMMA group and in 3 eyes in the acrylic group. In addition, one additional posterior capsulorhexis without anterior vitrectomy was performed in each group. Primary outcome measure was the occurrence of postoperative "complications" (fibrin, synechiae, posterior capsular opacification). For statistical evaluation, the Fisher exact test was used. RESULTS: When evaluating all complications together (at least one complication vs no complication), there were significantly less complications in the acrylic group (2 of 10 vs 15 of 20; p=0.007. For early complications (postoperative fibrin, synechiae) the difference was also significant (1 of 10 in the acrylic vs 11 of 20 in the PMMA group; p=0.02). The rate of posterior capsular opacification necessitating YAG capsulotomy was lower in the acrylic group (1 of 10 eyes) than in the PMMA group (7 of 20 eyes), but the difference did not reach statistical significance ( p=0.67). The postoperative time point of YAG capsulotomy was 21 months in the acrylic group and 19+/-10 months (range 6-33 months) in the PMMA group. IOL dislocation was not observed in any of the patients. Postoperative visual acuity was comparable in the two groups: 0.57+/-0.35 (0.03-1.0) in the acrylic vs 0.39+/-0.34 (0.001-0.9) in the PMMA group ( p=0.83). CONCLUSIONS: Implantation of hydrophobic acrylic intraocular lenses in the capsular bag in children may be associated with less postoperative complications compared with implantation of PMMA lenses. This appears also to be true in children under age 6 years. The visual results seem comparable and correspond mainly to the underlying ocular pathology.

Acrylates↗

PubMed2003

Bagging tree classifiers for laser scanning images: a data- and simulation-based strategy.

Diagnosis based on medical image data is common in medical decision making and clinical routine. We discuss a strategy to derive a classifier with good performance on clinical image data and to justify the properties of the classifier by an adapted simulation model of image data. We focus on the problem of classifying eyes as normal or glaucomatous based on 62 routine explanatory variables derived from laser scanning images of the optic nerve head. As learning sample we use a case-control study of 98 normal and 98 glaucomatous subjects matched by age and sex. Aggregating multiple unstable classifiers allows substantial reduction of misclassification error in many applications and bench mark problems. We investigate the performance of various classifiers for the clinical learning sample as well as for a simulation model of eye morphologies. Bagged classification trees (bagged-CTREE) are compared to single classification trees and linear discriminant analysis (LDA). We additionally compare three estimators of misclassification error: 10-fold cross-validation, the 0.632+ bootstrap and the out-of-bag estimate. In summary, the application of our strategy of a knowledge-based decision support shows that bagged classification trees perform best for glaucoma classification.

Case-Control Studies↗

PubMed2003

New glaucoma classification method based on standard Heidelberg Retina Tomograph parameters by bagging classification trees.

PURPOSE: In this article we propose and evaluate nonparametric tree classifiers that can handle non-normal data and a large number of possible predictors using the full set of standard Heidelberg Retina Tomograph measurements for classifying glaucoma. METHODS: The classifiers were trained and tested using standard Heidelberg Retina Tomograph parameters from examinations of 98 subjects with glaucoma and 98 normal subjects of the Erlangen Glaucoma Registry. All patients and control subjects were evaluated by 15 degrees -optic disc stereographs, Heidelberg Retina Tomograph measurements, standard computerized white-in-white perimetry, and 24-hour-intraocular pressure profiles. The subjects were matched by age and sex. Standard classification trees as well as bagged classification trees were used. The classification outcome of the trees was compared with the classification by two published linear discriminant functions based on Heidelberg Retina Tomograph variables with respect to their cross-validated misclassification error. RESULTS: The bagged classification tree had the lowest misclassification error estimate of 14.8% with a sensitivity of 81.6% at a specificity of 88.8%. The cross-validated error rates of the two linear discriminant function procedures were 20.4% (sensitivity 82.6%, specificity 76.7%) and 20.6% (sensitivity 81.4%, specificity 77.3%) for our set of observations. Bagged classification trees were able to reduce the misclassification error of glaucoma classification. CONCLUSIONS: Bagged classification trees promise to be a new and efficient approach for glaucoma classification using morphometric 2- and 3-dimensional data derived from the Heidelberg Retina Tomograph, taking into account all given variables.

Case-Control Studies↗

PubMed2002

[Comparison of precision of the TonoPenXL with the Goldmann and Draeger applanation tonometer in a sitting and recumbent position of the patients -- a clinical study on 251 eyes].

PURPOSE: Comparison of precise intraocular pressure (IOP) measurement with TonoPenXL, Goldmann and Draeger applanation tonometer in a sitting and recumbent position. MATERIAL AND METHODS: The IOP of 251 eyes of 127 consecutive patients (SFB 539) was measured prospectively in a sitting position (1 x Goldmann, 3 x TonoPenXL) and in recumbent position (1 x Draeger, 3 x TonoPen). The mean of three TonoPenXL measurements was only accepted in a 5 % interval. Additionally, corneal ultrasonic pachymetry (Tomey, AL-2000), central corneal power, refractive error, gender and age were registered. RESULTS: The IOP measured with the TonoPenXL was in 92 % in a range of 2 mm Hg from the Goldmann standard. In a vertical position, the IOP TonoPenXL (16.7 +/- 4.5 mm Hg) was 0.2 mm Hg lower than the IOP Goldmann (16.9 +/- 5.1 mm Hg; regression analysis: IOP TonoPenXL = 1.78 + 0.88 IOP Goldmann). In a horizontal position, the IOP TonoPenXL (17.5 +/- 5.0 mm Hg) was 0.5 mm Hg higher as the IOP Draeger (17.0 +/- 5.3 mm Hg; regression analysis: IOP TonoPen = 0.34 + 1.016 IOP Draeger). Using the TonoPenXL, the IOP was 0.8 mm Hg higher in recumbent position than in a sitting position (regression analysis: IOP TonoPen recumbent position = - 2.27 + 1.19 IOP TonoPen sitting position). We found no relationship found between central corneal power, central corneal thickness and IOD measured with the TonoPenXL. CONCLUSIONS: The TonoPenXL is useful for IOP measurement in a sitting and recumbent position. The results are reproducible in 92% with the Goldmann-applanation tonometer. The ophthalmologist has a comfortable measurement and screening tool for consultations or IOP investigation under general anaesthesia.

Adult↗