PubMed Health⌕ Search

Biomedical subjects

T Prager

Publications and source records attributed to T Prager.

4 recordsLinked to original sources

Phase velocity and phase diffusion in periodically driven discrete-state systems.

We develop a theory to calculate the effective phase diffusion coefficient and the mean phase velocity in periodically driven stochastic models with two discrete states. This theory is applied to a dichotomically driven Markovian two-state system. Explicit expressions for the mean phase velocity, the effective phase diffusion coefficient, and the Pe clet number are analytically calculated. The latter indicates as a measure of phase-coherence forced synchronization of the stochastic system with respect to the periodic driving and exhibits a "bona fide" resonance. In a second step, the theory is applied to a non-Markovian two-state system modeling excitable systems. The results prove again stochastic synchronization to the periodic driving and are in good agreement with simulations of a stochastic FitzHugh-Nagumo system.

Journal Article↗

Stochastic resonance in a non-markovian discrete state model for excitable systems.

We study a non-Markovian three state model, subjected to an external periodic signal. This model is intended to describe an excitable system with periodical driving. In the limit of a small amplitude of the external signal we derive expressions for the spectral power amplification and the signal to noise ratio as well as for the interspike interval distribution.

Journal Article↗

1999 Costenbader Lecture. Outcome study in amblyopia: treatment and practice pattern variations.

This study retrospectively evaluates the results of amblyopia therapy and suggests hypotheses for future study. We address the various methods of treatment and evaluate the results from the most common therapy techniques. Practice pattern variations were analyzed in addition to the analysis of overall results. For ophthalmologists, there is a need to determine whether actual medical practice approaches the established standard of care, if it exists at all. How often are medical procedures, thought to be appropriate, based on anecdotal observation (case reports) rather than hard data (clinical trials)? The 3 types of vision loss evaluated were strabismic, anisometropic, and deprivation amblyopia. The methods of treatment studied were full-time patching part-time occlusion, penalization, and occlusion of the contact lens. Nine centers, thought to have private as well as indigent patients, were recruited to participate in this study. The centers responded by filling out an extensive questionnaire and sending the information through the World Wide Web for inclusion in a spreadsheet. This information was then collated, and various statistical programs tabulated the results. Although trends, as a consequence of therapy, are suggested from our retrospective analysis, concrete results can only arise from a randomized prospective study. The study included 279 patients. There were a similar number of male and female patients. Only 77% of the patients without fusion before treatment had either single binocular vision or peripheral fusion at the conclusion of therapy. The log improvement of vision was significant in each group. Factors that potentially influenced the results were severity of distance acuity in the amblyopic eye before treatment, duration of treatment, and length of daily patching. The paper suggests that worse vision, not better vision, at the beginning, predicts better outcome in terms of improvement of visual acuity. For example, visual acuity less than 20/70 at the initiation of treatment led to better visual results of geometric log improvement. Surprisingly, among the 9 centers studied, there was a statistically significant difference in many of the areas related to practice patterns. Patient compliance, which directly affects outcome, was highly variable and is a factor that may be readily influenced by the treating physician.

Amblyopia↗

Retinal changes associated with tamoxifen treatment for breast cancer.

PURPOSE: This study was undertaken to estimate the incidence of retinal changes and determine the prevalence of ocular toxicity associated with tamoxifen treatment in a breast cancer population. METHODS: The study was based on a population cross-sectional survey, including 290 patients taking tamoxifen from 6 months to 12 years; 274 patients were analysed. The main outcome measures were the incidence of retinal changes and visual impairment. RESULTS: The incidence of retinal changes was 0.9% (3 of 274 patients). All 3 patients were asymptomatic. The length of tamoxifen treatment ranged from 39 months to 120 months in the affected patients, with cumulative tamoxifen doses ranging from 23.7 g to 73 g. CONCLUSIONS: Retinopathy in patients receiving low doses of tamoxifen is rare and, in our study, did not result in changes in visual acuity. We found no retinopathy in patients receiving tamoxifen within the first 3 years of treatment or in patients receiving a total tamoxifen dosage of less than 23.7 g. Although retinopathy can occur in a tamoxifen-treated population, its low incidence and an associated good prognosis for vision does not merit special screening for this problem.

Aged↗