Zeiss Humphrey II-i series, User Manual

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STATPAC Analysis & Printing
Humphrey Field Analyzer II-
i
series User Manual 2660021145640 A
7-10
The Change Analysis Printout
The Change Analysis printout shows analyses of up to sixteen (16) test results on one sheet. With
this analysis, STATPAC gives you an analytical summary of changes in the patient’s visual field. The
changes are monitored from the time of the earliest test you have included in the summary to the
time of the most recent test included.
STATPAC presents the Change Analysis in the form of a box plot analysis of test results, a summary
of global indices, and a linear regression analysis of Mean Deviation. The indices are the same ones
presented in the Single Field Analysis, but this time they are plotted over time to indicate changes in
the patient’s visual field.
The Box Plot
Box plots are helpful in making a quick determination about the nature and extent of visual field
changes over time. The box plot is a modified histogram that gives a five-number summary of the
test results. It displays a concise summary of the Total Deviation decibel values for each test,
showing the median, the two extreme values and the 15th and 85th percentile deviations.
The summary is made up of the differences at each tested point between the patient’s measured
field and the STATPAC age-corrected reference field. You can see in
Figure 7.4 that STATPAC plots the
median difference (the three dark lines shown at (a) inside the box), the 85th and 15th percentile
differences (the top and bottom of the box) as well as the extreme values of these differences (the
100th and zero percentile), or the end points of the line shown at (b).
Look at the box plots in Figure 7.4 and Figure 7.5 . The three things to note are:
1. The overall shape of the box, how elongated or compact it is.
2. The location of the three dark lines inside the box that indicate the median (a).
3. The top and bottom end points of the line along which the box lies (b).
(b)
(a)
(b)
100% best value=maximum positive deviation from age normal
85% 85th percentile
50% median
15% 15th percentile
0% worst value=maximum negative deviation from age normal
Figure 7.4 The Box Plot