Zeiss Humphrey II-i series, Руководство пользователя

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STATPAC Analysis & Printing
Humphrey Field Analyzer II-
i
series User Manual 2660021145640 A
7-12
A visual field with a deep scotoma covering a small number of points will result in a box plot in
which the box is more or less normal and there is a long tail. When a scotoma deepens over time,
the length of the tail increases.
If the scotoma enlarges to involve more than 15% of the points tested, the lower limit of the box will
be further depressed, and depending on the extent and gravity of the field loss, the boxes may be
very elongated.
The box plot section of the Change Analysis printout gives the dates of the tests included in the
analyses. The Change Analysis printout is available for the 24-2 and 30-2 test patterns, as well as
combinations of 24-2 and 30-2 tests, but not for the 10-2 pattern. If 24-2 and 30-2 tests are mixed
in the Change Analysis printout, the box plots and global indices are calculated only on the 24-2
portion of the 30-2 test results.
Change Analysis Summary Of Global Indices
The lower half of the Change Analysis printout displays summaries of the global indices MD (Mean
Deviation) and PSD (Pattern Standard Deviation). The summary results are presented chronologically
and in the same order as in the box plots. Thus, test dates may be taken from the box plot.
To facilitate interpretation, the p < 5% and p < 1% limits for the normal population are shown as
dashed reference lines. If, for example, the symbol indicating a test appears above the 5% line, the
index value on the test is not significant at the 5% level. If it falls below the 5% line, the index value
is significant at the 5% level. Similarly, if the symbol falls below the 1% line, the index value is
significant at the 1% level; that is, less than 1% of the normal population has an index value as
large as or larger than that found in the test.
Linear Regression
If five or more fields are analyzed on a Change Analysis printout, and all test results to be analyzed
were run with the same strategy, STATPAC will automatically perform a linear regression analysis of
mean deviation (MD). One of two messages, MD SLOPE NOT SIGNIFICANT or MD SLOPE
SIGNIFICANT, will be printed below the MD plot when a linear regression analysis has been
performed. The calculated slope of MD in decibels per year and a tolerance for that slope, expressed
as a p value, will also be printed.
A “significant” message means that it is likely that mean deviation has changed in the direction of
the estimated slope, and the lower the “p” value, the more likely it is. However, it remains for the
clinician to establish whether this indication on the test results is caused by progressive field loss or
by other factors.
A linear regression analysis tests the hypothesis that a slope is zero; that is, that there have been no
changes in the patient’s visual field. If this hypothesis is rejected after analysis at the p < 5% level,
the slope is said to be significant and the analysis continues at the 1% and 0.1% levels of
significance. The result is then displayed as being significant at p < 5%, p < 1%, or p < 0.1%.
Not only is the significance level of the slope important but also the magnitude of the slope. If, for
example, the MD slope is -3.6 dB per year, plus or minus 0.9, this means that there is a 95%
confidence level that the slope is between -2.7 and -4.5 dB per year. The slope is significant at a “p”