CenterVue
COMPASS Operating Manual
Pag. 27 di 53
10.2
Reliability indices
COMPASS provides standard methods to assess the reliability of a subject in performing the visual
field test:
False Positives
: these are trials in which no stimulus has been projected, therefore the
subject is not expected to respond. If this index exceeds 25% the number will show in red,
indicating possibly poor reliability.
False Negatives
: during the test, certain stimuli are randomly selected and retested at
brighter level than has been previously seen. If the patient does not respond, a false
negative instance is recorded. If this index exceeds 25%, the number will show in red,
indicating possibly poor reliability.
Blind Spot Test
: during the test stimuli are projected with high luminance, at random times,
at the blind spot location that has been selected prior to the start. Index shows the number
of positive responses obtained over the total number of such BS projections. If this index
exceeds 25%, the number will show in red, indicating possibly poor reliability.
COMPASS provides one additional parameter to be considered when assessing the reliability of a
certain test:
Average pupil size
: shows the average pupil diameter throughout the test. If this index is
below 3.0 mm, the number will show in red, indicating possibly poor reliability.
Fig. 22
– Detail of Exam review screen with reliability indices
Fixation plot / Area
Differently than in non-retinal tracked perimeters, the COMPASS fixation plot shown in a
test report (see par. 11.2 and Fig. 23 below) is not to be considered a way to assess the
reliability of a subject / test.
In fact, the plot shows fixation losses, as determined by tracking eye movements (see
par. 9.11), but these movements are taken into account and compensated at the time of
projection of the stimuli, therefore they do not necessarily degrade a test reliability.
Fig. 23
– Fixation plot and Area
