Biomedical subjects

Matthias Korth

Publications and source records attributed to Matthias Korth.

5 recordsLinked to original sources

PubMed2003

Cyclic summation versus m-sequence technique in the multifocal ERG.

BACKGROUND: The m-sequence technique is a typical tool for the multifocal ERG. The use of LEDs instead of a computer monitor enables a new technique that merits closer investigation: The cyclic summation technique. The aim of this study was to compare the two methods. METHODS: Six normal right eyes were examined with the RETIscan system using DTL electrodes. With an LED array (display diameter 52 degrees, 103 segments, 1 foveal + 102 arranged in six concentric rings) we studied: (1). first order kernels (m-sequence); (2). 30-Hz flicker responses (m-sequence); (3). 30-Hz flicker responses (cyclic summation). The three methods were tested with a pattern of concentric rings generated by selective deactivation of LEDs (the central LED and rings 2, 4 and 6; rings 1, 3 and 5 remained active). In each case six cumulative measurements (40 s each) were made and stored separately. To determine the signal-to-noise ratio, the average mf ERG response to all active LEDs was divided by the average response to the inactive ones. RESULTS: 1. Using cyclic summation the signal-to-noise ratio exceeds the signal-to-noise ratio of both m-sequence-controlled stimuli about twofold. This implies also better spatial resolution with the cyclic summation technique 2. Since the signal-to-noise ratio increases faster with the cyclic summation technique than with the m-sequence technique, the gain of time in mf ERG can reach 80%. CONCLUSION: As far as the signal-to-noise ratio and measuring time is concerned, the cyclic summation technique outmatches the m-sequence technique in mf ERG.

Adult↗

PubMed2003

Sequential classification in glaucoma diagnosis.

BACKGROUND: Large-scale screening in glaucoma diagnosis is expensive and time consuming. Sequential classification strategies can provide an effective combination of time-efficiency and diagnostic accuracy for glaucoma screening. METHODS: In a cross-sectional clinical study, a sequential diagnostic strategy, based on several psychophysical and electrophysiological tests, was evaluated on measurements from 595 eyes from 310 patients with primary open-angle glaucoma, and 419 eyes from 213 control subjects (age range 18-70 years in each group). Patients and controls successively underwent up to five psychophysical and electrophysiological diagnostic tests. Optic disc morphometry was taken as gold standard. Adapting group sequential techniques, sensitivity and specificity for the whole diagnostic program were controlled, allotting overall error rates of 10%. The criteria for the diagnostic process were developed in a learning sample (677 eyes) and verified in a validation sample (337 eyes). RESULTS: In the validation sample, 62.0% of the examined eyes could be classified, using a sequential 15-min two-step program. An overall 13.6% "gain" of saved time, compared to non-sequential discriminant analysis, was achieved without loss of diagnostic accuracy. A sequential 45-min five-step program classified 68.8% of the whole sample before morphometry, saving approximately 39% of examination time, compared to taking the complete discriminant score. CONCLUSION: Especially in screening, where the use of time-consuming and complicated diagnostic procedures is restricted, the implementation of testing programs based on group sequential strategies might be a promising means of saving personnel resources and reducing inconvenience for patients.

Adolescent↗

PubMed2003

A statistical model for the evaluation of sensory tests in glaucoma, depending on optic disc damage.

PURPOSE: To analyze the sensitivity of various sensory tests adjusted for glaucomatous optic disc damage. METHODS: In a cross-sectional study, the results of testing of 196 control subjects (age range, 18-69 years) and 308 patients with chronic open-angle glaucoma (age range, 18-70 years) were included. The perimetric mean defect (MD), a temporal contrast sensitivity test (TCS), a spatiotemporal contrast sensitivity test (STCS), the peak time of a blue-on-yellow visual evoked potential (BYVEP), and the amplitude of a pattern-reversal electroretinogram (PERG) were evaluated by a specific logistic regression model. This model included glaucomatous damage, quantified by neuroretinal rim area corrected for disc size, as a covariate of sensitivity. RESULTS: Sensitivity of diagnostic tests increased for all procedures with increasing loss of neuroretinal rim area. With progressing optic disc damage, MD and STCS showed higher sensitivity than did TCS. BYVEP showed a higher sensitivity than PERG in all disease stages. In general, the psychophysical tests were more sensitive than the electrophysiological ones. CONCLUSIONS: The specific model used in this study was an appropriate tool to analyze the sensitivity of several sensory glaucoma tests in relation to disease stage. Moreover, tests that were more sensitive in early disease stages (TCS) and others that were more sensitive in more advanced stages (MD, STCS) were identified.

Adolescent↗

PubMed2002

Testing for glaucoma with frequency-doubling perimetry in normals, ocular hypertensives, and glaucoma patients.

BACKGROUND: The aim of this study was to evaluate the diagnostic usefulness of the FDT perimeter protocol (C-20-5) in combination with a database system for analysis of single test locations. METHODS: One hundred seventy-three ocular hypertensive eyes, 116 "preperimetric" open-angle glaucoma eyes (glaucomatous optic disc atrophy, elevated intraocular pressure, no visual field defects in standard white-on-white perimetry), 199 "perimetric" open-angle glaucoma eyes (glaucomatous optic disc atrophy and visual field defects), and 151 control eyes underwent FDT screening and conventional white-on-white perimetry. Four repeated measurements were carried out in 15 glaucoma patients at 2-h intervals to judge reproducibility of all test locations. The present screening strategy begins testing at the normal 5% probability level. If a stimulus is not detected, further targets are presented. FDT-Viewfinder and statistics software were used for case-wise recalculation of all missed localized probability levels and correlation with corresponding test locations using conventional perimetry. RESULTS: Analysis of repeated measurements in patients reveals that variation of single test points can be considerable. However, the numbers of missed test-stimuli calculated globally or in quadrants are significantly correlated with corresponding Octopus visual field defects (Spearman rank correlation P<0.001). Using a predefined specificity of 96% in control eyes, 11% of ocular hypertensive eyes, 28.5% of "preperimetric" glaucoma eyes and 86.9% of "perimetric" glaucoma eyes have been classified glaucomatous using an overall score and with consideration of different cut-off points in right and left eyes. CONCLUSION: Point-wise analysis of FDT screening results can be helpful for classification of patient groups and consideration of the individual learning curve in repeated measurements. The C-20-5 protocol of the FDT perimeter is able to detect a considerable proportion of glaucomatous patients.

Adult↗

PubMed2002

Monitoring glaucoma progression with visual evoked potentials of the blue-sensitive pathway.

PURPOSE: To determine the value of visual evoked potentials with blue-on-yellow pattern stimulation in follow-up of glaucoma. METHODS: This prospective longitudinal concurrent study included a heterogeneous cohort of two groups, perimetric (n = 161) and preperimetric (n = 118), of patients with chronic open-angle glaucoma and 113 healthy control subjects. In the preperimetric glaucoma group, patients showed glaucomatous abnormalities of the optic disc, maximum intraocular pressure higher than 21 mm Hg, and unremarkable computerized visual field examination results. Patients underwent up to three VEP measurements with blue-on-yellow pattern stimulation, as well as qualitative and morphometric evaluation of color stereo optic disc photographs. Mean follow-up time between measurements was 24 months. VEP measurements were separately analyzed in preperimetric subjects, with and without progression of optic nerve damage. Progression of glaucoma was defined as increasing loss of neuroretinal rim. RESULTS: A separate analysis of VEP peak times in patients in the preperimetric group, with and without progression of glaucomatous optic nerve damage, showed no significant difference at baseline but a significant prolongation (P = 0.01) in patients with progressive disease, 2 years before morphologic changes were evident. VEPs in patients with nonprogressive disease were statistically unchanged during the observation period. The perimetric group and both preperimetric groups showed significantly prolonged VEP peak times in comparison with the control group (P < 0.001). CONCLUSIONS: In addition to photographic evaluation to detect glaucomatous disc atrophy, the blue-on-yellow VEP may be an objective electrophysiological tool for monitoring patients with glaucoma, because peak times are significantly associated with progression of optic nerve damage.

Chronic Disease↗