False Negative Errors; Fluctuation Values - Zeiss HUMPHREY 720i User Manual

6-6

False negative errors

Fluctuation values

REV. B 02/03 PN 51680-1
Occasionally during a test, a stimulus is repeated at a particular location and at a level much
brighter than has already been seen. If the patient does not respond to this trial stimulus, a
false negative error is recorded.
The printout will show the total number of false negative errors followed by the total number of
trials. If errors exceed 33% of the trials, "XX" will appear on the screen and the printout. A
high false negative score may indicate a fatigued patient, inattentive patient or a malingerer, but
it is also commonly seen in reliable patients who have genuine significant visual field loss. SITA
test results will not be marked "XX".
Note: SITA Standard and SITA Fast test results will display False Negative results as percent-
ages, not as fractions, and display the final percentage on the printout. A False Negative
value (in fraction form) will be displayed on the screen during the test. Because the SITA
strategies analyze the data at the end of the test before displaying final values, use the
False Negative value printed with the results if the display and printout values differ.
The fluctuation value is an option that can be used with the Full Threshold and FastPac
strategies. Fluctuation is not measured when using either of the SITA strategies. When
fluctuation is turned on, the threshold is measured twice at 10 pre-selected points. The HFA II
then calculates a fluctuation value on the basis of the differences between the first and second
measurements at each of the 10 points. This value is an index of how reliable a patient's
responses were during the test.
A patient who is very consistent will have a low fluctuation value, while a patient whose
responses vary significantly will have a high value. All fluctuation values significantly outside the
normal limits will be flagged on the printout with p values, e.g. p < 0.01.
The fluctuation option will add about 10% to the test time. When test results are analyzed with
STATPAC, the fluctuation value is used in the calculation of CPSD, one of the four global
indices. If the fluctuation is turned off, the CPSD will not be calculated. A discussion of
p values, STATPAC and global indices can be found in Section 7.
A high fluctuation value may be the first sign of glaucomatous field loss in patients who are
otherwise reliable subjects. It is also associated with established field loss in reliable subjects.
On the other hand, a high fluctuation value may simply indicate that the patient was inattentive
or did not understand the test.
HUMPHREY FIELD ANALYZER II -
TEST RELIABILITY
i
series