Biomedical subjects

Michael Bach

Publications and source records attributed to Michael Bach.

At least 19 recordsLinked to original sources

PubMed2007

The Freiburg Visual Acuity Test-variability unchanged by post-hoc re-analysis.

BACKGROUND: The Freiburg Visual Acuity and Contrast Test (FrACT) has been further developed; it is now available for Macintosh and Windows free of charge at http://www.michaelbach.de/fract.html . The present study sought to reduce the test-retest variability of visual acuity on short runs (18 trials) by post-hoc re-analysis. METHODS: The FrACT employs advanced computer graphics to present Landolt Cs over the full range of visual acuity. The sequence of optotypes presented follows an adaptive staircase procedure, the Best-PEST algorithm. The Best-PEST threshold obtained after 18 trials was compared to the result of a post-hoc re-analysis of the acquired data, where both threshold and slope of the psychometric function were estimated via a maximum-likelihood fit. RESULTS: Testing time was 1.7 min per run on average. Test-retest reproducibility was +/-2 lines (or +/-0.2 logMAR) for a 95% confidence band (using 18 optotype presentations per test run). Post-hoc psychometric fitting reproduced the Best-PEST result within 1%, although the individual slopes varied widely; test-retest reproducibility was not improved. CONCLUSIONS: The FrACT offers advantages over traditional chart testing with respect to objectivity and reliability. The similarity between the results of the Best-PEST vs. post-hoc analysis, fitting both slope and threshold, suggest that there is no disadvantage to the constant slope assumed by Best PEST. Furthermore, since variability was not reduced by post-hoc analysis, for high reliability more trials should be employed than the 18 trials per run used here.

Adult↗

PubMed2007

High prevalence of restless legs syndrome in somatoform pain disorder.

UNLABELLED: Patients with somatoform pain often complain of sleep disorders, but sleep disorders are not an integrated part of the diagnosis of this disorder. Restless legs syndrome is associated with painful symptoms and sleep disturbances. The aim of our study was to evaluate the prevalence of restless legs syndrome (RLS) in somatoform pain disorder. METHOD: In this study 100 consecutive patients (mean age: 46.4; SD: 11.4; women: 58) diagnosed with somatoform pain disorder (SPD) were clinically investigated for the occurrence of RLS at the behavioral medicine clinic for pain outpatients in the department of psychiatry within the Medical University of Vienna. The pain parameters of SPD were assessed using a pain questionnaire and visual analogue scales (VAS). The severity of RLS was established using the questionnaire of the International Restless Legs Syndrome Study Group (IRLSSG). RESULTS: The prevalence of restless legs syndrome found in somatoform pain disorder was 42%. Interrupted sleep was found in 83.3% in somatoform pain disorder with comorbid RLS and in 64.1% in somatoform pain disorder without RLS. Patients with continuous somatoform pain had a significant higher occurrence of RLS (Sample: 55%; with RLS: 71.4% and without RLS: 43.1%). The pain parameters increased parallel to the severity of RLS. Additionally, RLS was associated with higher psychosocial disability in family life. CONCLUSIONS: The prevalence of RLS is high in our sample of patients with somatoform pain disorder. There seems to be a difference in pain profile between patients with and without RLS. RLS may increase the pain level and prolong pain in somatoform pain disorder. RLS should be considered when a somatoform pain disorder is diagnosed.

Adult↗

PubMed2006

The influence of luminance on the multifocal ERG.

PURPOSE: To assess the efficacy of high luminance in increasing the amplitude of the multifocal electroretinogram (mfERG). We examined 5 male and 5 female volunteers in the age of 22-52 years (median 28 years). Three different stimulus luminance levels were applied: the bright areas of the stimulus pattern were set to 150, 300 and 500 cd/m(2). We recorded the potentials via DTL electrodes using the VERIS Science 4.4 system with 61 hexagons, pupils were dilated. Analysis was based on the 5 ring averages. RESULTS: Across all hexagons and subjects, the response density (approximately amplitude) rose by 20% when increasing the luminance by a factor of 3.3. The peak times decreased slightly with higher luminance, by less then 1.5 ms. CONCLUSIONS: Combining the present results with those from two previous studies, the gain (= relative amplitude increase for relative luminance increase) is close to 0.4 over a range of 56-700 cd/m(2). The stimulus luminance range suggested in the mfERG guidelines seems well chosen.

Adult↗

PubMed2006

ISCEV Standard for Clinical Electro-oculography (EOG) 2006.

The Clinical Electro-oculogram (EOG) is an electrophysiological test of function of the outer retina and retinal pigment epithelium (RPE) in which the change in the electrical potential between the cornea and the ocular fundus is recorded during successive periods of dark and light adaptation. This document sets out a Standard Method for performance of the test, and also gives detailed guidance on technical and practical issues, and on reporting test results. The main object of the Standard is to promote consistent quality of testing and reporting within and between centres. This 2006 Standard, from the International Society for Clinical Electrophysiology of Vision (ISCEV: www.iscev.org ), is a revision of the previous Standard published in 1993, and reviewed and re-issued in 1998.

Adaptation, Ocular↗

PubMed2006

Bistable perception -- along the processing chain from ambiguous visual input to a stable percept.

The observation of an ambiguous figure leads to spontaneous perceptual reversals while the observed picture stays unchanged. Some ERP studies on ambiguous figures report a P300-like component correlated with perceptual reversals supporting a top-down explanation, while other studies found early visual ERP components supporting a bottom-up explanation. Based on an experimental paradigm that permits a high temporal resolution of the endogenous reversal event, we compared endogenous Necker-cube reversals with exogenously-induced reversals of unambiguous cube variants. For both reversal types, we found a chain of ERP components with the following characteristics: (1) An early occipital ERP component (130 ms) is restricted to endogenous reversals. (2) All subsequent components also appear with exogenously-induced reversals, however 40-90 ms earlier than their endogenous counterparts. (3) The latency difference between reversal types is also reflected in the timing of manual reactions, which occur 100-130 ms after P300-like components. The results suggest that the P300-like component is the same as found in other ERP studies on ambiguous figures. This component does not reflect the reversal per se, but rather its cognitive analysis, 300 ms after a change of the representation in early visual areas. The presented ERP chains integrate the different ERP results and allow to pinpoint the steps where top-down mechanisms begin to exert their influence.

Electroencephalography↗

PubMed2006

PI 3-kinase pathway is responsible for antiapoptotic effects of atrial natriuretic peptide in rat liver transplantation.

AIM: To investigate the in vivo effect of atrial natriuretic peptide (ANP) and its signaling pathway during orthotopic rat liver transplantation. METHODS: Rats were infused with NaCl, ANP (5 microg/kg), wortmannin (WM, 16 microg/kg), or a combination of both for 20 min. Livers were stored in UW solution (4 degrees C) for 24 h, transplanted and reperfused. Apoptosis was examined by caspase-3 activity and TUNEL staining. Phosphorylation of Akt and Bad was visualized by Western blotting and phospho-Akt-localization by confocal microscopy. RESULTS: ANP-pretreatment decreased caspase-3 activity and TUNEL-positive cells after cold ischemia, indicating antiapoptotic effects of ANP in vivo. The antiapoptotic signaling of ANP was most likely caused by phosphorylation of Akt and Bad, since pretreatment with PI 3-kinase inhibitor WM abrogated the ANP-induced reduction of caspase-3 activity. Interestingly, analysis of liver tissue by confocal microscopy showed translocation of phosphorylated Akt to the plasma membrane of hepatocytes evoked by ANP. CONCLUSION: ANP activates the PI-3-kinase pathway in the liver in vivo leading to phosphorylation of Bad, an event triggering antiapoptotic signaling cascade in ischemic liver.

Animals↗

PubMed2006

What does the WHOQOL-Bref measure? Measurement overlap between quality of life and depressive symptomatology in chronic somatoform pain disorder.

INTRODUCTION: Quality of life has become an important outcome criterion for psychiatric interventions. Especially in chronic disorders with no complete recovery, the improvement of quality of life is an important treatment goal. Nevertheless, there are methodological problems in assessing quality of life. There is a possible measurement overlap between quality of life and psychopathology, especially depression, which may invalidate research results. This study addresses the quality of life of patients with chronic somatoform pain and its relation to depressive symptoms. METHOD: One hundred out-patients with somatoform pain disorder at the Behavioural Medicine Pain Clinic in the Department of Psychiatry of the Medical University of Vienna were diagnosed using the SCID for Diagnostic and Statistical Manual of Mental Disorder (DSM-IV). The patients filled out the World Health Organisation Quality of Life Assessment-Bref (WHOQOL-Bref) and the Beck Depression Inventory (BDI). Pain intensity (average pain, maximum pain, minimal pain) and disability (work, leisure and family life) were assessed using visual analogue scales. RESULTS: Quality of life in somatoform pain disorder was reduced compared to the norm population, especially in the physical and psychological domains. There were highly significant negative correlations between, on the one hand, depressive symptomatology (BDI) and, on the other hand, the physical quality of life domain (r=-0.655, p<0.01), the psychological domain (r=-0.735, p<0.01), the social domain (r=-0.511, p<0.01) and the environmental domain (r=-0.561, p<0.01). In all domains of the WHOQOL-Bref and in the global score, significant differences between the group of patients with severe or very severe depressive symptoms and the group with no or only mild depressive symptoms were found. DISCUSSION: While the WHOQOL-Bref showed a poor quality of life of patients with chronic somatoform pain disorder in general and especially in the physical and in the psychological domains, the high correlation of physical and psychological quality of life scores with depressive symptomatology points to a measurement overlap. It is suggested that assessment of subjective quality of life should always be checked for the influence of depressive symptomatology on the quality of life score.

Chronic Disease↗

PubMed2006

Measuring contrast sensitivity under different lighting conditions: comparison of three tests.

PURPOSE: The purpose of this study was to evaluate three psychophysical tests for the measurement of contrast sensitivity (CS) and disability glare (DG) at different luminance levels. METHODS: In 60 eyes of 60 individuals (group 1: 20 healthy eyes of young individuals; group 2: 20 healthy eyes of elderly subjects; group 3: 20 eyes with nuclear cataract), CS with best correction was measured twice with the Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS) and the Functional Acuity Contrast Test (FACT, 1.5 cycles per degree [cpd]) at 167 cd/m2 and 0.167 cd/m2, and with the Pelli-Robson Chart (PRC) at 100 cd/m2 with and without glare. Repeatability of test and retest, and discriminative ability between the different subgroups, were assessed for CS values. RESULTS: Maximum CS values varied across tests. In all groups, highest CS values were obtained with the photopic FF-CATS. For FACT scores at 1.5 cpd, there was a ceiling effect for young subjects. CS scores obtained with the PRC were the lowest. The PRC had the best test-retest repeatability of all tests. Under mesopic conditions with glare, reliability was generally lower; the FF-CATS had the highest repeatability of the mesopic tests. The FF-CATS discriminated best between the different groups for all conditions. CONCLUSIONS: There are large discrepancies in the test results between CS testing methods, especially under different lighting conditions. Results from different CS tests are not interchangeable.

Adult↗

PubMed2006

Ocular prevalence and stereoacuity.

BACKGROUND: Most people attribute a higher weight to the input from one eye than to that from the other eye when they have to align stereodisparate objects in the same visual direction. This preference for visual directions has been termed 'ocular prevalence', according to the Latin praevalentia = superior power. QUESTIONS: (1) Is ocular prevalence of one eye (or its correlate, partial suppression of the other eye in the prevalence task) restricted to large stereodisparities, close to Panum's limit, or does it occur also at small stereodisparities, near the stereoscopic threshold? (2) Is ocular prevalence a handicap for stereoacuity? METHODS: Six non-strabismic observers with equal visual acuity of their two eyes were examined. To determine their ocular prevalence, they were presented with vertical vernier lines at stereodisparities ranging between 30 and 430 arcsec. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. Their stereoscopic threshold was measured with an adaptive staircase procedure, using the Freiburg Stereoacuity Test. RESULTS: All six observers exhibited some ocular prevalence. It changed considerably on repeated measurements. In three observers, it even switched from one eye to the other. Ocular prevalence occurred not only at large stereodisparities, close to Panum's limit, but also at small stereodisparities. The stereoscopic threshold of the six observers ranged between 1.7 and 12.3 arcsec. CONCLUSION: Ocular prevalence is common, intra-individually variable and occurs even at small stereodisparities close to the stereoscopic threshold. It is compatible with 'optimal' stereoacuity. Hence, ocular prevalence appears to be a harmless feature of normal binocular vision.

Adult↗

PubMed2006

Pattern ERG as an early glaucoma indicator in ocular hypertension: a long-term, prospective study.

PURPOSE: The conversion rate from untreated ocular hypertension (OHT) to glaucoma is only approximately 1% per year. Discrimination of nonconverters and potential converters would help reserve preventative treatment for those who need it and thus avoid unnecessary side effects and expenditure for those who do not. This prospective study was designed to assess the pattern electroretinogram (PERG) as an early indicator of dysfunction preceding glaucoma. METHODS: Ninety-five eyes of 54 patients with intraocular pressure > or =25 mm Hg (or > or =23 mm Hg with additional risk factors), normal visual fields, normal optic disc cupping, and visual acuity > or =0.8 were evaluated. Every 6 months during a median follow-up of 8.2 years, the PERG and visual fields were obtained besides other standard diagnostics. PERGs were recorded in steady state mode in response to checkerboard stimuli at 15 reversals/s, and the amplitudes in response to check sizes of 0.8 degrees and 16 degrees as well as the ratio of the amplitude of responses to 0.8 degrees over that to 16 degrees checks were determined. RESULTS: Glaucomatous visual field defects developed in eight eyes. For the PERG to 0.8 degrees checks and for the PERG ratio, analysis of the receiver-operating characteristic (ROC) yielded steadily increasing ROC areas before conversion (i.e., an increasing ability of the PERG to predict nonconversion or conversion). One year before conversion, the ROC area of the PERG ratio was 0.78; at a threshold of 1.06 this corresponded to a sensitivity of 80% and a specificity of 71%. CONCLUSIONS: The PERG can help to predict stability or progression to glaucoma in OHT at least 1 year ahead of conversion.

Adult↗

PubMed2006

Visual acuities "hand motion" and "counting fingers" can be quantified with the freiburg visual acuity test.

PURPOSE: The visual acuity (VA) of patients with very low vision is classified using the semiquantitative scale "counting fingers" (CF), "hand motion" (HM), "light perception" (LP), and "no light perception." More quantitative measures would be desirable, especially for clinical studies. The results of clinical VA measurements, Early Treatment Diabetic Retinopathy Study (ETDRS) charts, and the Freiburg Visual Acuity Test (FrACT) were compared. The FrACT is a computerized visual acuity test that can present very large Landolt C optotypes when necessary. METHODS: Examined were 100 eyes of 100 patients with various eye diseases (e.g., diabetic retinopathy, ARMD), covering a range of VAs from LP to decimal 0.32. The FrACT optotypes were presented on a 17-inch LCD monitor with random orientation. After extensive training, two ETDRS and FrACT measurements were obtained. The testing distance was 50 or 100 cm. RESULTS: ETDRS and FrACT coincided closely for VA > or = 0.02 (n = 80). ETDRS measures were successfully obtainable down to CF (at 30 cm; test-retest averaged over all patients, coefficient of variation [CV](ETDRS) = 9% +/- 8%), and FrACT provided reproducible measurements down to HM (test-retest CV(FrACT) =12% +/- 11%). For CF (n = 6), both ETDRS and FrACT resulted in a mean VA of 0.014 +/- 0.003 (range, 0.01-0.02). The VA results of FrACT for HM (n = 12) were 0.005 +/- 0.002 (range, 0.003-0.009); the individual values were highly reproducible. No results were obtainable for LP (n = 2). CONCLUSIONS: The three acuity procedures concur above a VA of 0.02. The results suggest that the category CF at 30 cm can be replaced by 0.014, using ETDRS or FrACT. Using FrACT, one can even reproducibly quantify VA in the HM-range, yielding a mean VA of 0.005.

Adult↗

PubMed2005

Motion adaptation: net duration matters, not continuousness.

Motion processing is strongly adaptable. Adaptation strength generally increases with motion duration. Little is known, though, about the effect of motion onsets and offsets, which might be relevant if adaptation is not based on motion duration per se, but on the recent cumulated activity of motion-processing mechanisms. Thus, we presented intermittent motion with three different onset rates for adaptation. The duty cycle was kept constant at 33% while the rate of motion onsets was either 1.4, 2.8, or 5.6 per second. Stationary stimuli and continuous motion were used as reference conditions. The amplitude of the N2 component of human motion visual evoked potentials was used to quantify adaptation. All three onset rates induced virtually identical amounts of adaptation (occipitally, P=0.71; occipito-temporally, P=0.27), suggesting that the continuousness of the stimulus does not play an important role in motion adaptation. This was confirmed by measuring the motion aftereffect psychophysically.

Adaptation, Physiological↗

PubMed2005

Magnetic resonance imaging in patients with obsessive-compulsive disorder with good versus poor insight.

The DSM-IV provides two subtypes of obsessive-compulsive disorder (OCD), labelled as OCD with insight and OCD with poor insight. For the latter, patients generally fail to recognize that the obsessions or compulsions are excessive or unreasonable. Several studies have shown significant brain abnormalities in OCD patients. However, at present, it remains unclear whether a specific pattern of structural brain abnormalities is related to poor insight in OCD. In the present study, magnetic resonance imaging (MRI) findings were compared in OCD patients with insight versus those with poor insight. Outpatients with diagnoses of OCD according to DSM-IV (300.30) and ICD-10 (F42) (n = 84; mean age 38+/-13; 35 females, 49 males) were dichotomized into the two subtypes. All subjects underwent an MRI examination. MRI findings were rated as "MRI abnormality" and "normal MRI." In our sample, 48% of the patients had MRI abnormalities. There was a highly significant difference between the two groups according to frequencies of MRI abnormalities, with 83% of the patients with poor insight showing MRI abnormalities compared with only 21% of the patients with insight. The specifier "poor insight" helps to identify a subgroup of OCD with a higher frequency of brain abnormalities of various types. This distinction should be taken into account in future studies concerning the course and therapeutic outcome of OCD.

Basal Ganglia↗

PubMed2005

Ten-year results: detection of long-term progressive optic disc changes with confocal laser tomography.

BACKGROUND: The detection of a slowly progressive loss of optic nerve fibres in patients with ocular hypertension is a very important task for confocal laser tomography. We compared changes of the parameters of the Heidelberg Retina Tomograph (HRT) with changes of static visual field measurements. METHODS: Since 1994, patients with ocular hypertension have been monitored prospectively every 6 months with visual field measurements (Octopus 123, dG1x) as well as examinations of the optic disc using the HRT. A progressive excavation of the optic nerve head was defined as a significant increase or decrease of the linear regression over time. We analysed the HRT parameters cup area (CA), cup volume (CV), cup shape measure (CSM), rim volume (RV), retinal nerve fibre thickness (RNFLT) and contour height variation (CHV) each circular and for six different sectors of 109 eyes (60 patients). A glaucomatous visual field defect and therewith the conversion from ocular hypertension (OHT) to open angle glaucoma (OAG) was defined as reproducible defect-cluster >20 dB of two or three single points at the same location. RESULTS: Nine of 109 eyes converted from OHT to OAG. A significant linear increase of the circular parameters occurred in two (CA), four (CSM), two (CV) and a decrease in three (CHV), two (RV) and four (RNFLT) eyes. The sectoral analysis increased the results of CA and CV in the temporal superior and temporal inferior sectors (ts/ti): five/four (CA), two/three (CV). Cup shape measure showed in the temporal superior, temporal inferior (ti) and nasal inferior (ni) sectors slightly increased hits [five (ts), five (ti), five (ni)]. CONCLUSIONS: The linear model for the progression of the optic disc parameters detected only a small amount of the converters. The hit rate could be increased with the sectoral based analysis. Cup shape measure showed the highest rate.

Diagnostic Techniques, Ophthalmological↗

PubMed2005

Visual acuity and X-linked color blindness.

PURPOSE: Optimal sampling for visual acuity requires a fine array of cones with identical sensitivity. Thus, dichromats, whose inner fovea is made up of cones having the same spectral sensitivity, may have better than normal visual acuity. We investigated this by comparing the visual acuities of trichromats and X-linked dichromats, while taking into account the different molecular genetics underlying the disorder. METHODS: Our subjects were age- and refraction-matched groups of normals (n=8) and X-linked dichromats (n=13). The dichromats (four protanopes and nine deuteranopes) were genotyped and classified according to whether they carried a single (n=6) or multiple (n=7) visual pigment genes on their X-chromosome. Visual acuity was measured in both eyes with the Freiburger Visual Acuity Test. RESULTS: Normal trichromats and ungenotyped dichromats do not significantly differ in visual acuity, nor do ungenotyped protanopes and deuteranopes. However, multi-gene dichromats, who possess more than one photopigment gene in the array, all of which encode for the same long- or middle-wavelength sensitive photopigment, have significantly higher visual acuity than either normal trichromats or dichromats who have only a single-gene. CONCLUSIONS: Multi-gene dichromats may benefit from a reduction in chromatic aberration and chromatic noise in the high acuity channel, normally a consequence of combining signals from different cone photoreceptor types and of cone-specific patterns of retinal image defocus and blur. Single-gene dichromats may not share in the advantage because of other molecular differences that influence the development of the retinal mosaic and/or its visual pathways.

Adult↗

PubMed2005

The Necker cube--an ambiguous figure disambiguated in early visual processing.

How can our percept spontaneously change while the observed object stays unchanged? This happens with ambiguous figures, like the Necker cube. Explanations favor either bottom-up factors in early visual processing, or top-down factors near awareness. The EEG has a high temporal resolution, so event related potentials (ERPs) may help to throw light on these alternative explanations. However, the precise point in time of neural correlates of perceptual reversal is difficult to estimate. We developed a paradigm that overcomes this problem and found an early (120 ms) occipital ERP signal correlated with endogenous perceptual reversal. Parallels of ambiguous-figure-reversal to binocular-rivalry-reversals are explored.

Adult↗

PubMed2005

Pattern specificity of human visual motion processing.

Visual motion processing is strongly susceptible to adaptation. A variety of patterns have been used as stimuli in previous studies. Three of these, namely random dots, barcode-like gratings, and sinusoidal gratings, were compared in the present study using motion-onset visual evoked potentials (VEPs). We assessed the effects of the adaptation pattern and the test pattern to which the VEP is recorded. Furthermore, we evaluated the interaction between both, i.e. whether differences between adaptation and test pattern affect the response. Isodirectional and antidirectional adaptation were used to differentiate between the actual motion adaptation and associated flicker adaptation. Motion adaptation was almost 2.5-fold stronger (p < 0.01) if the same rather than different pattern types were used for both adaptation and test. This implies that separate neural populations are involved, suggesting the presence of pattern-tuned motion mechanisms.

Adaptation, Ocular↗

PubMed2004

Vernier acuity for stereodisparate objects and ocular prevalence.

QUESTION: How precisely can objects, located in different depth planes, be aligned to the same visual direction? METHODS: Twenty normal observers were presented with vertical Vernier lines at various stereodisparities. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. RESULTS: Over a stereodisparity range from zero to 62'', the threshold for detecting a lateral offset between the Vernier lines remained at the "hyperacuity" level of about 7''. With larger stereodisparities, the threshold increased about fourfold, probably due to a mutual, partial suppression of the position signals from the right and left eyes. The reference point from which the observers judged the relative visual directions between stereodisparate objects was not located midway between the eyes; rather, it was often decentred towards the right or the left eye, meaning that the observers had an "ocular prevalence". Their ocular prevalence was, however, not strong enough to have an effect on the Vernier acuity for stereodisparate objects. (Under pathological conditions like strabismic amblyopia, one should expect a 100% prevalence of the good eye, implying that the Vernier acuity reaches the monocular level, irrespective of any depth difference between objects.) CONCLUSION: Vernier acuity decreases with increasing stereodisparity. Ocular prevalence, occurring frequently among persons with normal eyes, has no effect on Vernier acuity for stereodisparate objects. For a typical everyday viewing condition, the reduced Vernier acuity beyond a stereodisparity of 62'' means that, from a viewing distance of 40 cm, precision mechanics have to guide their instrument as close as 0.4mm to a workpiece, until they can utilise their best position acuity.

Adult↗