Zeiss HUMPHREY 720i User Manual - page 123
STATPAC ANALYSIS & PRINTING RESULTS
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REV. B 02/03 PN 51680-1
HUMPHREY FIELD ANALYZER II -
i
series
Total deviation plots
On the left in the lower half of the Single Field Analysis printout is a pair of plots, one above the
other, labeled Total Deviation. The numeric values in the upper portion of these plots represent
the difference in decibels (dB) between the patient’s test results and the age-corrected normal
values at each tested point in the visual field.
The lower total deviation plot, called a probability plot, translates the values in the upper plot
into shaded symbols which indicate the statistical significance of each decibel deviation. These
are explained in the legend labeled Probability Symbols. The darker the symbol the less likely
it is that the field is normal in that location (although the likelihood of abnormality also
depends upon the actual prevalence of disease in the patient population). For instance, a
totally black square indicates that the deviation from normal found at that point location
occurs in fewer than 0.5% of normal subjects. Notice that this probability statement is made on
a point-by-point basis, allowing the practitioner to read the results like an isopter plot or
graytone.
Pattern deviation plots
To the right of the total deviation plots in the Single Field Analysis printout are two additional
plots, labeled Pattern Deviation. These are similar to the total deviation plots, except
that here STATPAC has adjusted the analysis of the test results for any changes in the height of
the measured hill of vision caused, for example, by cataracts or small pupils. Similarly,
STATPAC corrects for any patients who are “supernormal”, adjusting the expected hill of vision
upward by the appropriate amount and thereby making the analysis more sensitive to localized
scotomas.
Thus, the numeric Pattern Deviation plot shows the deviation in decibels from the age-
corrected normal values, adjusted for any shift in overall sensitivity. The pattern deviation
probability plot indicates the statistical significance of the result at each point. Again, the
darker the symbol the more significant the deviation from the normal threshold value.
Global indices
A short table labeled Global Indices appears on the far right side of the page. Here
STATPAC has made some calculations to provide overall guidelines to help the practitioner
assess the field results as a whole rather than on the point-by-point basis shown in the Total
Deviation and Pattern Deviation plots. The four global indices are calculated from deviations in
the age-corrected normals data. The “p” (probability) values for the global indices, discussed
below, do not need to be corrected again for age.
Mean Deviation (MD) is the average elevation or depression of the patient’s overall field
compared to the normal reference field. If the deviation is significantly outside the population
norms, a “p” value is given. For example, if p
normal population shows an MD larger than that found in this test. Categories for p values are
p
A significant MD may indicate that the patient has an overall depression, or that there is
significant loss in one part of the field and not in others. MD is best interpreted in relation to
the Total and Pattern Deviation charts.
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