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Oliver Ehrt

Publications and source records attributed to Oliver Ehrt.

8 recordsLinked to original sources
PubMed2005

Foveal contour interaction: detection and discrimination.

Contour interaction, the detrimental effect of flanking features on the discrimination of optotypes, has been studied mainly close to the visual acuity limit. We were interested to know how these results compare with those for the detection of targets. According to the simplest model of contour interaction, comparable detection effects would be expected. The case for low-level masking would be further strengthened if the form and nature of the dependence on flank separation and flank polarity followed that typically found in studies of lateral spatial masking [Vision Res. 33, 993 (1993)]. Landolt Cs subtending a visual angle of 0.25 degrees, 0.5 degrees, and 1.0 degrees were presented and contrast thresholds for detecting the presence of the Landolt C and discriminating its orientation were measured in five normal subjects as a function of flank separation and flank polarity. The results obtained for the relationship between detection and discrimination depend on the size of the target used. For small letters, discrimination but not detection was significantly affected by flanking bars. For large letters, detection and discrimination were affected to the same extent. However, in this case the effectiveness of opposite-polarity flanks and the finding that facilitation occurred at close, not far, flank separations suggests that the simplest explanation in terms of masking may not be applicable.

Differential Threshold↗
PubMed2004

Integration of orientation information in amblyopia.

A recent report suggests that amblyopes are deficient in processing local orientation at supra-threshold contrasts. To determine whether amblyopes are also poor at integrating local orientation signals, we assessed performance for an orientation integration task in which the orientations of static signals are integrated across space. Our results show that amblyopic visual systems can integrate local static oriented signals with the same level of efficiency as normal visual systems. Although internal noise was slightly elevated, there was no indication that fewer samples were used to achieve optimal performance. This finding suggests normal integration of local orientation signals in amblyopia.

Adult↗
PubMed2003

Orbital rhabdomyosarcoma in Noonan syndrome.

The incidence of various benign and malignant tumors is increased in patients with Noonan syndrome compared with the general population. We present a 9-year-old boy with the typical features of Noonan syndrome and an acute nonaxial proptosis of the right eye. An ultrasound scan, a computed tomography scan, and magnetic resonance imaging raised suspicion of rhabdomyosarcoma. Biopsy confirmed the diagnosis. The tumor was consequently treated with combined chemotherapy and radiotherapy. Rhabdomyosarcoma is a rare but important differential diagnosis of tumor formation in children with Noonan syndrome and may arise in the orbit.

Brachytherapy↗
PubMed2003

Foveal contrast thresholds exhibit spatial-frequency- and polarity-specific contour interactions.

Traditionally, contour interaction has been investigated at the visual acuity limit using a Landolt C and flanking bars, performance being quantified in terms of a percent correct measure. More recently, it has been shown that the properties of the contour interaction are different when larger stimuli are used: Contour interaction is not polarity specific, and spatial frequency tuning for an unflanked C is broader. Here we quantify contour interaction for stimuli 5x larger than the resolution limit in terms of contrast thresholds. We show that polarity of bars has little effect on unfiltered stimuli but does show very different effects on the spatial-frequency-tuning curves for discrimination of the Landolt C. This explains the polarity dependence of crowding at the visual acuity limit and its independence for larger unfiltered targets. Thus the underlying filtering function is composed of more than one mechanism, affected differently depending on the relative polarity of the test and flank contours.

Contrast Sensitivity↗
PubMed2002

[Application of the new coding standards for introducing diagnosis related groups (DRGs) in ophthalmology].

For all in-patients a fundamental change of hospital financing based only on diagnosis related groups (DRGs) is planned in Germany for 2004. Patients are grouped into different DRGs according to their coded diagnoses, operations and procedures. Hence, the quality of coding is essential for adequate reimbursement of cases and thus for hospital financing. The legal framework of coding is supplied by the so-called "general and special coding guidelines for coding diseases and procedures", presented jointly by the associations representing hospitals and public and private health insurance companies in early 2002. These German coding standards regulate how coding must be performed in daily practice and therefore have a major influence on the grouping of patients into DRGs. Because of their importance this paper describes the practical application of current coding standards. Specifically in Ophthalmology the problem exists that for many procedures adequate coding numbers are still missing, thus impairing further development of the DRG system.

Diagnosis-Related Groups↗
PubMed2002

Effect of inferior oblique recession in strabismus sursoadductorius.

UNLABELLED: The aim of this retrospective study was a quantitative analysis of the effect of graded inferior oblique recessions (8 mm, 10 mm or maximal) in strabismus sursoadductorius. METHOD: 234 patients (2-81 years of age) with unilateral strabismus sursoadductorius and stereopsis were operated between 1990 and 1999. Maximal recession (14.6 mm) included an anteroposition to the lateral aspect of the insertion of the inferior rectus. Before and three months after the operation, horizontal and vertical deviations (VD) were assessed by cover testing in five positions of gaze. In 121 patients, additional subjective quantitative assessment, including cyclodeviation measurement, was carried out with Harms' tangent screen. RESULTS: The mean effect of the operation on VD in 25 degrees adduction increased from 6 degrees with 8 mm recession to 10 degrees with maximal recession. It was related more to the amount of preoperative VD in adduction than to the amount of recession. One patient had a limitation of elevation with a hypotropia of >4 degrees, 7% needed further surgery because of undercorrection. DISCUSSION: Maximal recession of the inferior oblique muscle is a suitable procedure even in patients with marked strabismus sursoadductorius. The rate of functional undercorrection is low and there is no risk from general anesthesia or significant postoperative limitation of elevation.

Adolescent↗