Biomedical subjects

R Lämmer

Publications and source records attributed to R Lämmer.

4 recordsLinked to original sources

PubMed2006

[Flicker provocation with LED full-field stimulation in normals and glaucoma patients].

BACKGROUND: Flicker light is an easy method to test sensory function after stress. The aim of this study was to determine the influence of flicker stress on temporal contrast sensitivity in healthy controls and patients with glaucomatous alteration of the optic disk. METHODS: A commercially available full-field stimulator (Retiport, Roland Consult) equipped with white LEDs was modified to perform psychophysical tests. The patients underwent measurements of the recovery time interval from cessation of flicker stress until recognition of a pregiven flicker contrast after photo stress. In addition, we studied contrast sensitivity with a continuous flickering target and with a flicker burst protocol avoiding adaptation to prevailing flicker. All tests were performed at a constant retinal illumination and at a frequency of 37 Hz for provocation as well as for contrast sensitivity tests. SUBJECTS: Normal healthy controls (40), "preperimetric" (62), and "perimetric" (52) open-angle glaucoma patients were studied. Exclusion criteria were age lower than 31 years, visual acuity under 0.6, and perimetric mean defect more than 9.5 dB. RESULTS: Recovery time after flicker stress was significantly longer in patients than in normals and longer in perimetric than in preperimetric patients. Analysis in perimetric patients revealed a larger area under ROC for the provocation test (0.95) than in contrast sensitivity tests (continuous flicker method: 0.90, flicker burst mode: 0.84). CONCLUSION: High-power LEDs which are installed in modern full-field devices can be used as a helpful tool to study psychophysical properties. In the present study it could be shown that threshold, adaptation, and recovery of temporal transfer characteristics are impaired in many patients with glaucoma.

Contrast Sensitivity↗

PubMed2006

[Healthy optic discs with large cups--a diagnostic challenge in glaucoma].

BACKGROUND: Healthy optic discs with large cups are often characterised to be glaucomatous in automated, morphometric analysis. The aim of this study was to investigate the variables of laser scanning tomography (LST) and nerve fibre polarimetry of these disks in comparison to small and normal sized disks. METHODS: 117 eyes (age 49.3 +/- 14.6 years) with healthy, non-atrophic disks (md = 0.8 dB, Tensio 14.3 +/- 2.5 mmHg) of the Erlangen Glaucoma Registry were clinically examined. Morphometry was performed both by planimetry and the HRT I (Heidelberg Engineering, Dossenheim, version 2.01) and with the GDx FCC (Laser Diagnostics, San Diego). 63 eyes initially referred for a large cup were compared to 54 normal eyes. All measurements were analysed globally and in four sectors according to Jonas. RESULTS: The disc area of discs with large cups was significantly larger than that for the normals (3.1 +/- 5.3 vs. 2.2 +/- 4.2 mm (2)). Both the multivariate analysis of the HRT and the GDx revealed a significant correlation with total disk area (R = 0.34, p = 0.0001), with a high percentage of false positive glaucoma eyes among large disks. Cup area and volume showed, in contrast to rim volume and rim area, a significant correlation (R = 0.76, p = 0.0001) with the disc size. Thickness of retinal nerve fibre layer measurements both in HRT and GDx showed higher values for larger disc size with steeper cup measurements. The vertical diameter of the cup increased in comparison to the horizontal to a higher extent with increasing disc size. CONCLUSIONS: By the pronounced enlargement of cup measurements, decreasing nerve fibre thickness values and decreasing ratio of temporal-to-inferior width of the neuroretinal rim, large disks may easily be detected as false glaucomatous by morphometric analysis systems. A better presentation of large discs in a normative database and integration of sectors and disc area in a multivariate analysis may improve the diagnostic abilities of automated morphometric disk analysis.

Diagnosis, Differential↗

PubMed2005

Automated segmentation of the optic nerve head for diagnosis of glaucoma.

Glaucoma is the second most common cause of blindness worldwide. Low awareness and high costs connected to glaucoma are reasons to improve methods of screening and therapy. A well-established method for diagnosis of glaucoma is the examination of the optic nerve head using scanning-laser-tomography. This system acquires and analyzes the surface topography of the optic nerve head. The analysis that leads to a diagnosis of the disease depends on prior manual outlining of the optic nerve head by an experienced ophthalmologist. Our contribution presents a method for optic nerve head segmentation and its validation. The method is based on morphological operations, Hough transform, and an anchored active contour model. The results were validated by comparing the performance of different classifiers on data from a case-control study with contours of the optic nerve head manually outlined by an experienced ophthalmologist. We achieved the following results with respect to glaucoma diagnosis: linear discriminant analysis with 27.7% estimated error rate for automated segmentation (aut) and 26.8% estimated error rate for manual segmentation (man), classification trees with 25.2% (aut) and 22.0% (man) and bootstrap aggregation with 22.2% (aut) and 13.4% (man). It could thus be shown that our approach is suitable for automated diagnosis and screening of glaucoma.

Algorithms↗

PubMed2004

[Telematic-assisted self-tonometry (TAS)].

BACKGROUND: Close supervision of intraocular pressure (IOP) means monitoring an important risk factor for glaucoma. METHOD: After instruction in its use, patients measure their own IOP several times a day with the Drager self-tonometer. The measurements are subsequently transmitted to a server via the telephone keypad and recorded separately for each patient. The software enables statistical evaluation of the pressure levels collected. RESULTS: Up to now 30 of 35 patients transmit measurements or had done so for at least 6 months. Registration of measurement levels covering months and years provides the opportunity for optimizing treatment and hence can be considered a start toward quality assurance in the treatment of glaucoma patients. CONCLUSION: TAS is a cost-efficient method for obtaining long-term profiles of eye pressure. Thus, the possibility exists for early therapeutic intervention in patients at risk. The compliance gained by the close relationship between the physician and the patient represents a positive prognostic factor.

Equipment Design↗