Frequency dependency of temporal contrast adaptation in normal subjects

AbstractThe aim of this study was to determine the influence of temporal frequency of temporal contrast adaptation on contrast sensitivity in healthy subjects. Temporal contrast sensitivities (TCS) were measured monocularly in seven healthy subjects with a modified ERG full-field bowl stimulator at eight different test temporal frequencies (9, 15, 20, 25, 31, 37, 44, 51Hz) using a two-alternative-forced-choice strategy. Before each presentation of the test stimulus, a 100% contrast adapting flicker stimulus was presented (frequencies: 9, 15, 20, 25, 31, 37, 44, 51, 100Hz). At each adapting frequency, a complete set of TCSs was measured. All temporal contrast sensitivities decreased with increasing temporal frequencies. Adaptation led to a general temporal contrast sensitivity decrease. Largest adaptation effects were seen at an adaptation frequency of 25Hz. Reduction of contrast sensitivity was significantly larger at 25Hz adaptation than at 9Hz adaptation (t-test of paired samples, Bonferroni corrected). The results of this study showed a general TCS decrease with the largest effect at an adaptation frequency of 25Hz. This finding indicates that the contrast adaptation probably occurred in the magnocellular-pathway. In future clinical studies adaptation effects could be investigated in patients with reduced temporal contrast sensitivity

Ensemble Pruning for Glaucoma Detection in an Unbalanced Data Set

Background: Random forests are successful classifier ensemble methods consisting of typically 100 to 1000 classification trees. Ensemble pruning techniques reduce the computational cost, especially the memory demand, of random forests by reducing the number of trees without relevant loss of performance or even with increased performance of the sub-ensemble. The application to the problem of an early detection of glaucoma, a severe eye disease with low prevalence, based on topographical measurements of the eye background faces specific challenges. Objectives: We examine the performance of ensemble pruning strategies for glaucoma detection in an unbalanced data situation. Methods: The data set consists of 102 topographical features of the eye background of 254 healthy controls and 55 glaucoma patients. We compare the area under the receiver operating characteristic curve (AUC), and the Brier score on the total data set, in the majority class, and in the minority class of pruned random forest ensembles obtained with strategies based on the prediction accuracy of greedily grown sub-ensembles, the uncertainty weighted accuracy, and the similarity between single trees. To validate the findings and to examine the influence of the prevalence of glaucoma in the data set, we additionally perform a simulation study with lower prevalences of glaucoma. Results: In glaucoma classification all three pruning strategies lead to improved AUC and smaller Brier scores on the total data set with sub-ensembles as small as 30 to 80 trees compared to the classification results obtained with the full ensemble consisting of 1000 trees. In the simulation study, we were able to show that the prevalence of glaucoma is a critical factor and lower prevalence decreases the performance of our pruning strategies. Conclusions: The memory demand for glaucoma classification in an unbalanced data situation based on random forests could effectively be reduced by the application of pruning strategies without loss of performance in a population with increased risk of glaucoma

Temporal contrast sensitivity: A potential parameter for glaucoma progression, especially in advanced stages

INTRODUCTION. Previously it could be shown that temporal contrast sensitivity is affected by glaucoma and maximally influenced after 25-Hz adaptation in normals. This study investigated different kinds of 25-Hz temporal contrast adaptation on TCS in patients with ocular hypertension, preperimetric primary open-angle glaucoma, and perimetric open-angle glaucoma. Additionally, correlations of measured data with parameters of glaucoma diagnostic were done and assessed for the potential use of TCS as a parameter for glaucoma progression. MATERIALS AND METHODS. One hundred and four subjects were included: 44 normals, 14 ocular hypertensions, 11 preperimetric primary open-angle glaucomas, and 35 perimetric open-angle glaucomas. Using the Erlangen Flicker Test, temporal contrast sensitivity was measured without adaptation, after pre-adaptation and after pre- and re-adaptations at 25 Hz. Reliability analyses were done. RESULTS. All test strategies showed high reliability (a-Cronbach’s > 0.86). In normals, age-dependency of temporal contrast sensitivity without adaptation (p = 0.052) and after pre- and re-adaptation (p = 0.008) was observed. Temporal contrast sensitivity is significantly reduced after pre-adaptation for all subjects (p < 0.001). Reduction of temporal contrast sensitivity after pre- and re-adaptations was significant in all groups (p < 0.001), but it was smaller than after single pre-adaptation (p < 0.001). Temporal contrast sensitivity without adaptation was significantly reduced in patients with perimetric glaucoma (p = 0.040) but not in patients with ocular hypertension and preperimetric glaucoma. Correlation analyses yielded a significant correlation between temporal contrast sensitivity without adaptation and mean defect (p = 0.003, r = –0.329), loss variance (p = 0.027, r = –0.256), and retinal nerve fibre layer thickness (p < 0.001, r = 0.413) for all subjects and between temporal contrast sensitivity after pre-adaptation and mean defect (p = 0.045, r = –0.239). CONCLUSIONS. Temporal contrast sensitivity seems to be affected in perimetric glaucoma with an overall reduction after adaptation. Significant correlations of temporal contrast sensitivity with perimetric and morphologic parameters offer new aspects of its potential use as a glaucoma progressions marker, especially in advanced stages when perimetric diagnosis is limited

Objective perimetry using a four-channel multifocal VEP system: correlation with conventional perimetry and thickness of the retinal nerve fibre layer

Purpose There is evidence that multifocal visual evoked potentials (VEPs) can be used as an objective tool to detect visual field loss. The aim of this study was to correlate multifocal VEP amplitudes with standard perimetry data and retinal nerve fibre layer (RNFL) thickness. Method Multifocal VEP recordings were performed with a four-channel electrode array using 58 stimulus fields (pattern reversal dartboard). For each field, the recording from the channel with maximal signal-to-noise ratio (SNR) was retained, resulting in an SNR optimised virtual recording. Correlation with RNFL thickness, measured with spectral domain optical coherence tomography and with standard perimetry, was performed for nerve fibre bundle related areas. Results The mean amplitudes in nerve fibre related areas were smaller in glaucoma patients than in normal subjects. The differences between both groups were most significant in mid-peripheral areas. Amplitudes in these areas were significantly correlated with corresponding RNFL thickness (Spearman R=0.76) and with standard perimetry (R=0.71). Conclusion The multifocal VEP amplitude was correlated with perimetric visual field data and the RNFL thickness of the corresponding regions. This method of SNR optimisation is useful for extracting data from recordings and may be appropriate for objective assessment of visual function at different locations

Time Course of Induced Astigmatism After Canaloplasty

Purpose:To study the changes in astigmatism after canaloplasty and to analyze its correlation with long-term intraocular pressure (IOP) results.Methods:Twenty-six eyes of 26 consecutive patients with primary open-angle glaucoma (n=14) and pseudoexfoliative glaucoma (n=12) undergoing canaloplasty were included in this retrospective study. Canaloplasty comprised of 360-degree catheterisation of Schlemm canal by means of a flexible microcatheter with distension of the canal by 2 tensioning 10-0 polypropylene sutures. Primary outcome measures included IOP, glaucoma medication usage, astigmatism, and adverse events at 2, 4, 12, and 24 weeks postoperatively.Results:The mean preoperative IOP was 21.15.8 mm Hg. The mean IOP decreased to 14.25 +/- 4.3 mm Hg at 6 months. Mean astigmatism preoperatively was 0.77 +/- 0.5 D, which increased to 3.3 +/- 1.7 D at 2 weeks postoperatively (P0.05; Wilcoxon-test). Thereafter, the astigmatism underwent a spontaneous decline, reaching 1.9 +/- 0.8 D at 4 weeks and 1.2 +/- 0.74 D at 12 weeks postoperatively. Best-corrected visual acuity did not change significantly. Six months after canaloplasty, mean astigmatism reached the preoperative range of 0.86 +/- 0.52 D. Astigmatism at 2 weeks correlated significantly and inversely with IOP at 6 months (r=0.59, P=0.005; Spearman).Conclusions:The change of astigmatism after canaloplasty follows a clear time course with a maximum at 2 weeks reaching preoperative values at 6 months. The amount of surgically induced astigmatism might be helpful to predict outcome of canaloplasty in terms of IOP reduction

The Erlangen Glaucoma Registry: a Scientific Database for Longitudinal Analysis of Glaucoma

Background: Due to the slow progression of the Glaucoma disease, a large study population and long-time observations are needed to gain insights into its long-term effects and progression rates. Since modalities can export data in machine-readable formats, statistical analyses of the large number of examinations is feasible. These data have been integrated in a central patient registry, the Erlangen Glaucoma Registry (EGR). Objectives: The primary focus of the EGR system design has been its fitness for analyses. It holds almost all the available research data for registered glaucoma patients. This allows for cross-sectional and longitudinal observations and for evaluation of prognostic validity of diagnostic procedures. Methods: An adequate technology for integration of data and flexibility in data analysis is a database management system (DBMS). Here, a careful schema design is mandatory. Adding new modalities leads to schema modifications which are supported by defining a core database schema and attaching all data to this core. On that basis, a large number of modalities have been connected to the EGR. Results: The registry contains data of 1,400 patients in the main longitudinal study. It has successfully helped in scientific research, as can be seen in a large number of published papers. For example, validation of new sensory physiological methods requires patients with reliable diagnoses. The existence of a well-documented patient collective facilitated finding such patients. Conclusions: The EGR holds a unique amount of available data gathered in large longitudinal studies. It was successful in terms of medical results obtained. Developed as an evolutionary system, it can easily be extended