Probability Level Classifications; Reliability Measures - Zeiss Humphrey matrix User Manual

PROBABILITY LEVEL CLASSIFICATIONS

The patient achieved a threshold level in the range that 95% (P>=5%) of normal sub-
jects of the same age achieved for the test locations with this shading.
The probability is less than 5% (P<5%) that a normal subject of the same age would
perform at the threshold level that this patient achieved for the test locations with this
shading.
The probability is less than 2% (P<2%) that a normal subject of the same age would
perform at the threshold level that this patient achieved for the test locations with this
shading.
The probability is less than 1% (P<1%) that a normal subject of the same age would
perform at the threshold level that this patient achieved for the test locations with this
shading.
The probability is less than 0.5% (P<0.5%) that a normal subject of the same age
would perform at the threshold level that this patient achieved for the test locations
with this shading. This shading will also occur if the patient failed to respond at the
maximum contrast level of the instrument (0 dB is indicated).

RELIABILITY MEASURES

When reviewing the results of the visual field test, give careful consideration to the reliability
indicators (catch trials). They are an important measure of patient reliability in taking the test
(and of the reliability of the results). They are indicated as a ratio of the number responded to the
number presented (as well as a percentage of the total). For example, 1/10 (10%) indicates that
the patient responded to 1 of the 10 catch trials presented.
FIXATION ERRORS - The ratio of the number of times the patient responded to a target placed
in the blind spot versus the total number of times fixation was tested (i.e., total number of
targets placed in the blind spot). Fixation errors indicate the patient is not maintaining good
fixation during the test, is misaligned, or does not understand the test.
FALSE POSITIVE ERRORS - The ratio of the number of times the patient responded to a
"pause" in the testing sequence (i.e., no target presented) versus the total number of "pauses"
in the testing sequence. False positive errors indicate the patient is pressing the button even if
the patient does not see any patterns (a "happy clicker") or does not understand the test.
FALSE NEGATIVE ERRORS - The ratio of the number of times the patient did not respond to a
test pattern at the maximum possible contrast level of the instrument versus the total number of
times that maximum possible contrast level patterns were tested. When possible, false negative
catch trials are only presented at locations where the patient has previously responded. False
negative catch trials are not used with screening tests. False negative errors indicate the patient
is likely not paying attention, does not understand the test, or has a severe loss at the location of
the false negative catch trial(s).
Humphrey Matrix Visual Field Instrument
Rev. D 08/21/06 PN 701692
19