Zeiss Humphrey II-i series, User Manual

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STATPAC Analysis & Printing
Humphrey Field Analyzer II-
i
series User Manual 2660021145640 A
7-6
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 (shown as “B” in
Figure 7.1 ). 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 from 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 (shown as “C” in
Figure 7.1 ). 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.
Removal of Pattern Deviation (PD) and Progression Analysis Plots for Severely Depressed Fields
Pattern Deviation (PD) analysis corrects for the effects of media opacities and other generalized field
loss by assuming that at least a few test points are not yet affected by localized scotomas—and
thus reflect only generalized loss. For severely depressed fields, when field loss becomes so
advanced that almost all points are involved in localized loss, then PD analysis is no longer effective.
While it is not possible to precisely predict when PD analysis has lost its usefulness, the effect
becomes increasingly prevalent as Mean Deviation (MD) approaches -20dB.
Specifically, when a visual field is severely depressed (MD => -20dB):
• The GHT is automatically set to “Outside Normal Limits”.
• The Pattern Deviation plot(s) for that exam will be replaced with “Pattern Deviation not shown
for severely depressed fields. Refer to Total Deviation.” This is true for all STATPAC printouts.
• On GPA Printouts, the Progression Analysis plot for that exam will also be replaced with
“Pattern Deviation not shown for severely depressed fields. Refer to Total Deviation.”
• The Progression Summary (“Possible Progression”, “Likely Progression”, etc.) will not be
printed.