No abstract

The development of an experimental automatic perimeter, the Scoperimeter, is described. We use an oscilloscope as campimeter screen for the examination of the central 25 degrees of the visual field. The oscilloscope beam generates a homogeneous background luminance (0.1 cd/m2) and single stimulus static stimuli in any given position. The effective luminance-range of the stimuli is 3.0-3.5 log.unit. The visual field examination is controlled by a small computer system. Four examination programs written in Basic, are described. The screening programs using threshold related suprathreshold stimuli appear to be the most efficient compromise between speed and accuracy of the examination. The printout of these programs consists of a noninterpolated grey-scale presentation. Other programs perform static meridional perimetry or measure luminance threshold in 60 regularly distributed positions in the visual field. We have taken into consideration the factors that may influence the outcome of the examination: the presence of an instruction phase, the possibility to follow the progress of the examination and careful stimulus-timing. In a second paper we present clinical results we obtained using our instrument.

Introduction Baroreflex sensitivity (BRS) is often presented as a single number, but it is actually a frequency-dependent phenomenon whose value changes constantly due to internal and external stimuli. The standing posture, for instance, necessitates a changeover from vagal to sympathetic predominance for cardiovascular control. We present a wavelet cross-spectral analysis of blood pressure (BP) and interbeat interval (IBI) recordings in the search for variations in gain and phase between these signals. Additionally, we show how the lag in sympathetic response dictates BP-to-IBI phase relations. Methods Recordings in supine and head-up tilted (HUT) position, obtained earlier in 10 healthy subjects (4f/6m, aged 27–47 years) were used. BP and IBI were measured from the continuous finger pressure (by Finometer). The cross-wavelet analysis produced time- and frequency dependent gain (wBRS, wavelet derived BRS) and phase, using the MATLAB ® wavelet toolbox. We also applied the wBRS method to model-generated BP- and IBI-data with known interrelations to test the results of this analysis technique. Finally, wBRS values were compared with the xBRS-approach, which is a time domain method for continuous BRS estimation in a sliding 10-s window. Results In resting supine conditions, wBRS fluctuates; more at respiratory frequencies than in the 0.1 Hz band. After HUT, wBRS at the respiratory frequency decreases from average 22.7 to 8.5 ms/mmHg, phase between BP and IBI increases from −30° to −54°; in the sympathetic 0.1 Hz range these numbers are 13.3→6.3 ms/mmHg and −54°→−59°. The values found by xBRS are intermediate between wBRS-resp and wBRS-0.1 Hz. The Appendix shows that for the simulated data the BRS and phase values as found by the wavelet technique can be explained from vector additions of vagal and sympathetic BRS contributions. Discussion During supine rest parasympathetic control of heart rate dominates BRS; after HUT this is diminished and less effective. Due to the reaction times of the autonomic effectors, the phase relations between the signals depend on the relative contribution of the sympathetics, which explains the larger phase shift. Conclusion Cross wavelet analysis allows to follow fast BRS changes in time and frequency, while the computed phase relations help understand sympathetic participation.

The Scoperimeter is an experimental automatic campimeter based on an oscilloscope connected with a microcomputer and a printer-plotter. The instrument has 60 stimuli in the 25 degrees visual field and uses a suprathreshold gradient-adapted threshold related strategy (1). The report describes the results of a comparative examination of the threshold related gradient-adapted suprathreshold detection and limited assessment programme in 20 eyes with normal visual fields, 24 eyes of patients with glaucomatous defects and 10 eyes of patients with (para) central defects due to maculopathies. The Scoperimeter detected all larger defects. The Scoperimeter detected 60% of very early glaucomatous defects. The remaining 40% was detected by high resolution (1 degree) manual meridional static perimetry. The configuration of defects was demonstrated satisfactorily only for homogeneous defects of considerable size. The strategy is quite satisfactory for the detection of glaucomatous defects provided the resolution is increased and the peripheral field can be examined. A high resolution threshold strategy serving as a data base for follow-up examination is under investigation. The Scoperimeter's low resolution grid and suprathreshold strategy are not suitable for the detection and assessment of small relative (para) central defects.

No abstract