Otometrics
69
Test Battery
Calorics test
4.7.5
SPV Analysis
Analysis of a nystagmographic measurement takes three steps:
• First, the software detects the position of the pupil in each captured frame of the
video stream. The result is the trace for horizontal and vertical eye position over
time.
• Second, an algorithm detects minimum and maximum velocity in the traces and
checks whether these are part of a valid nystagmus beat. If so, the algorithm
detects the slow phases.
• Third, the difference between the minimum and the maximum represents the
amplitude of a nystagmus beat, the difference of the time indexes of these mini-
mum and maximum represents the duration, the Slow Phase Velocity is the quo-
tient of both. Depending on the kind of performed tests, additional parameters
are calculated (e.g., culmination, fixation index, etc.).
4.7.6
Peak Frequency Calculation
Evaluating nystagmographic examinations by looking at the frequency is not recom-
mended. However, Vestlab is capable of determining the frequency of nystagmus
beats in a trace. Depending on the settings, the frequency can be calculated as an
average over the whole measurement, as an average of a 30 second period starting
30 seconds after the start of the measurement, or as an average of the 30 second
period around the culmination, which was determined by SPV analysis. If any, the
last method is preferable. Due to standards in nystagmographic tests, frequencies are
not calculated in Hertz which would cover a period over one second, but over a
30 second period.
4.7.7
Fixation Index Calculation
The average SPV in the fixation period divided by the fixation index average of the
SPV before the fixation period began results in the fixation index value. To determine
the SPV before the fixation, the software calculates the average of the last three nys-
tagmus beats before the fixation began. A fixation index of <25% is within normal
limits. The fixation light should be turned on right after the culmination phase in
order for the fixation index to be accurate.
Summary of Contents for Hortmann Vestlab 100
Page 1: ...Hortmann Vestlab 100 User Manual Doc no 7 50 0940_02 Part no 7 50 09400 0459 ...
Page 6: ...4 Otometrics Table of Contents Hortmann Vestlab 100 User Manual ...
Page 16: ...14 Otometrics Introduction Typographical conventions ...
Page 92: ...90 Otometrics Troubleshooting Vestlab Software ...
Page 100: ...98 Otometrics Technical Specifications Hortmann Vestlab 100 ...
