Viktor Scheiber

Intraoperative retinal light damage reflected in electrophysiologic data

In a series of 30 unilaterally pseudophakic patients, electroretinograms and electrooculograms were recorded 6 months postoperatively. The unoperated on fellow eyes served as controls High intraoperative retinal light exposure (3.4–7.3 mW/cm2, Zeiss OPMI 6 operating microscope) caused a substantial reduction of electrophysiologic potentials. Light protection prevented deterioration of electroretinogram and electro-oculogram potentials; reducing the bulb voltage, tilting the axis of illumination, filtering short wavelengths and the use of light shields resulted in 4-log-unit lower intensities (0.8–3.7 μW/cm2).

Fast Oscillation of the Corneoretinal Potential in Ischemic Retinopathy

Clinical electro-oculographic examinations were performed in 21 subjects with unilateral occlusion of the central retinal artery. The values from the unimpaired fellow eyes were used as normal data fo

The Fast Oscillation of the Electro- Oculogram

The dependence of amplitudes and peak latencies of the light-induced fast EOG oscillation was studied using rectangular light stimulation. A linear increase of the amplitude was observed in the intensity range tested (24–3,000 asb). No influence of the time of preadaptation to darkness on the amplitudes could be proven in a range of 20 s to 21 min. The peak latency was not dependent on light intensity. Prolonged peak latencies were observed following short and long periods of dark adaptation.

Comparison of electro-oculogram recording methods.

The purpose of this study was to compare the variability of the amplitude ratios and latencies of the electro-oculogram (EOG) light peak (LP) in three different recording conditions: Arden ratio (dark trough (DT): 12 min), modified Arden ratio (DT: 15 min) and light peak/dark baseline ratio (LP/BL: 35 min of dark adaptation). Additionally, EOGs from eyes with dilated and undilated pupils were recorded. The light intensity stimulating the eyes with dilated pupils was attenuated 1 log unit. The EOG amplitude ratios displayed no significant difference between the three conditions tested. The comparison of implicit times (time from onset of light exposure to LP) revealed significantly (p < 0.001) shorter values when the recording of the LP was preceded by a dark adaptation of 35 min. The broadening of the curves in DT/LP recordings might be caused by a superposition of a residual dark oscillation on the LP. The recordings from eyes with dilated pupils--stimulated with 1 log unit lower intensity--revealed lower amplitude ratios than the recordings from eyes with undilated pupils.

Berechnung der OC- und ASN-Funktionen geschlossener Sequentialtests bei Binomialverteilung

ZusammenfassungEs werden drei einander ausschließende Hypothesen über den Parameterp einer Binomialverteilung betrachtet:H1:p>0.5,H0:p=0.5,H−1:p<0.5. Mit Hilfe von geschlossenen Sequentialtestplänen soll eine Entscheidung zwischen den drei Hypothesen getroffen werden. Wichtige statistische Eigenschaften dieser Tests werden durch ihre OC- und ASN-Funktionen ausgedrückt. Es wird ein Algorithmus zur Berechnung dieser Funktionen und, zusätzlich, der VSN-Funktion beschrieben. Mit dieser Methode können auch die OC-, ASN- und VSN-Funktionen vonk-Stufenplänen (k≧2) berechnet werden.SummaryThree mutually exclusive hypotheses on the parameterp of a binomial distribution are considered:H1:p>0.5,H0:p=0.5,H−1:p<0.5. A decision in favour of one of these hypotheses is obtained by means of restricted sequential tests, with variable sample sizen (n≦nmax), the adequacy of which is characterized by their OC- and ASN-functions. An algorithm is described for the computation of these functions and, in addition, of the variance of sample number (VSN) function. This method can also be applied to the general case ofk-stage sampling plans (k≧2) to calculate their OC-, ASN-, and VSN-functions.

Prostacyclins in Diabetes: An Electrophysiological Study

Twelve patients with juvenile (insulin-dependent, type I) diabetes were treated either with prostacyclins or placebo in a double-masked randomized study. The electroretinogram (ERG) was recorded before, 1 day and 8 months after treatment. An analysis of variance and covariance was carried out to evaluate possible treatment or time effects on the a and b waves and the oscillatory potentials of the ERG. Mean values of potentials displayed a decrease of amplitude and an increase of latency over the follow-up period in all patients. No statistically significant difference between treated and placebo groups could be proven.

The dark trough in clinical electro-oculography. Influence of preadaptation on amplitudes and latencies.

The influence of four different intensities of the preadapting light on amplitude and implicit time of the dark-induced oscillation (dark trough) of the electro-oculogram was tested in 10 healthy individuals. The amplitude of the dark trough (normalized to preadapting baseline) was found to be dependent on the intensity of the preadapting light (analysis of variance:p < 0.0001). No correlation could be proven between preadapting light intensity and the implicit time of the dark trough (p = 0.299). The confidence intervals of the implicit time of the dark trough exceeded 14 minutes in all four intensity settings. There was no significant dependence of the absolute baseline values on preadapting intensities (p = 0.236).

Versuchspläne zur stochastischen Optimierung

ZusammenfassungIn der experimentell medizinischen Forschung mangelt es an Plänen zur Auffindung optimaler Stufenkombinationen von zwei oder mehr Faktoren. Dazu werdenk-dimensionale orthogonale zentrale zusammengesetzte Versuchspläne 2. Ordnung, bestehend aus einem vollständigen 2k-Plan oder einer geeigneten fraktionellen Replikation davon, einem oder zwei Axialplänen undz Versuchen im Mittelpunkt (z=0, 1, 2, ...) angeführt. Die Pläne unterscheiden sich hauptsächlich in der Genauigkeit, mit der die Regressionskoeffizienten, insbesondere die quadratischen, geschätzt werden, und im erforderlichen Versuchsbereich. Fallen zwei Axialpläne zusammen, so wird die vergrößerte Versuchsanzahl durch die Möglichkeit einer Adäquatheitsprüfung des Modells aufgewogen. Diese Pläne wurden in Anlehnung an die von Box und Wilson vor allem für Optimierungsprobleme in der chemischen Forschung angegebenen Prozeduren entwickelt. Falls erforderlich, können Begleitvariable durch entsprechende Kovarianzanalysen berücksichtigt werden.SummaryIn medical research there is a lack of experimental designs aiming at an optimal stage-combination of two or more factors. For this purposek-dimensional orthogonal central composite designs were constructed. They consist of a factorial 2k-design or of a suitable fractional replication, of one or two axial plans and ofz experiments in the center (z=0, 1, 2, ...). The designs differ in their precision of estimating the regression coefficients and, concomitantly, in the experimental region covered by them. If two axial plans coincide, the increase in the number of experiments is compensated by the possibility of testing the model for adequacy. These designs were based on procedures of Box and Wilson, which were primarily developed for optimization problems in chemical research. Inclusion of concomitant variables, if necessary, is provided for.

The ERG Off-Response in Ischemic Retinopathy

In ischemic retinopathy caused by central retinal artery occlusion the b-wave amplitude and the amplitude of the d-wave are impaired. A significant correlation exists between the amount of reduction of the amplitudes of these two components. This result supports the theory that b- and d-wave are controlled by the same retinal structures.