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GN Otometrics A/S 15
AccuScreen PRO User Manual Test Methods
2.1.3 Applications of OAEs
Identification of hearing loss
The presence of TEOAEs strongly indicates that a portion of the au-
diogram has hearing threshold levels better than 25 dB HL, and cor-
relates best with good hearing in the mid-frequency range. It is not
possible to rely on the TEOAE spectrum to predict threshold levels
by frequency. TEOAEs are well suited and widely accepted for the
purpose of screening hearing.
It has been hoped that DPOAEs would allow clinicians to predict be-
havioural thresholds, but this is not yet the case. However, there is
correspondence between DP-gram configurations and audiogram
configurations (i.e. in ears with sensory hearing loss, DPOAEs are
reduced or eliminated only for the stimulus frequency regions,
which coincide with the impaired region). Accordingly, DPOAEs
can give a better frequency specific impression of cochlear integrity
than TEOAEs, and are well suited to monitoring of cochlear func-
tion.
Differential diagnosis
While OAEs have not proven good predictors of auditory nerve tu-
mors, they nevertheless provide the opportunity to document nor-
mal or near-normal cochlear function. This makes them helpful in
pinpointing sites of lesion, as well as in making management deci-
sions.
2.1.4 How the AccuScreen PRO T-module determines a PASS
Applies to AccuScreen PRO T, TA, TD, TDA.
AccuScreen PRO uses a binomial statistical test to give either a PASS
or a REFER result. Most TEOAE instruments use the signal-averag-
ing technique with two buffers. In contrast, the AccuScreen PRO cal-
culates the statistical probability that an emission has been recorded
at a succession of sampling points ranging from 6 to 12 ms after the
end of the stimulus.
The AccuScreen PRO processes each of the sampled points individ-
ually. For each point, it is assumed that no time-locked signal (otoa-
coustic emission) is present. If this is true, then the distribution of
positive and negative deflections across sweeps at a point in the
waveform will be normal. Thus, the probability that a time-locked
signal is present can be determined by comparing the distribution of
positive and negative deflections at each data point to a normal dis-
tribution. The criterion level used by the AccuScreen PRO signal de-
tection algorithm for presence of a time-locked signal is 99.7%.
Each recorded sweep is assigned to one of eight quality buffers, ac-
cording to its amplitude. The statistical analysis is carried out simul-
taneously in each quality buffer, and the test result will be a
PASS if