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4-4
Test Results and Reliability Measures
For the N-30-F FDT full threshold test, the instrument utilizes a staircase threshold strategy
known as a Modified Binary Search (MOBS). The Humphrey Matrix utilizes a four-reversals
rule (N-30-F) for determining the threshold level. The range of possible threshold level
values for the raw data (patient threshold scores) is between 0 dB Maximum Contrast
(lowest patient sensitivity) and 56 dB Minimum Contrast (highest patient sensitivity). The
formula used to calculate the dB values is
from 1 (minimum contrast) to 2048 (maximum contrast) and H is approximately 2. Note
that XX is displayed if the threshold is not determined due to inconsistent patient
responses which do not meet the MOBS threshold criteria. The magnitude of the threshold
level values is directly correlated to the Field Analyzer values.
The 24-2, 30-2, 10-2 and Macula FDT full threshold tests are modeled after the Humphrey
Field Analyzer (HFA™) tests to provide visual field test results that are familiar. The FDT test
results for the threshold tests correlate with the HFA results, but they are not directly
comparable. The FDT tests use a large (~270 subjects for each eye) age normative FDT
database. The FDT full threshold tests use a maximum likelihood threshold strategy known
as ZEST (Zippy Estimate of Sequential Testing) to provide accurate threshold results as
quickly as possible. ZEST is similar to SITA used on the HFA, but differs in the specific
algorithm details.
The 24-2 (55-point) and 30-2 (69-point) FDT full threshold tests are central 30 degree
visual field tests for use in general visual field testing and glaucoma management. These
tests also provide a Glaucoma Hemifield Test that provides a plain language interpretation
of the visual field results based on an asymmetry analysis between test locations in the
upper vs. lower hemifield to detect glaucoma. The Glaucoma Hemifield Test (GHT)
messages include Within normal limits, Outside normal limits, Borderline, Borderline -
General reduction of sensitivity, General reduction of sensitivity, and Abnormally high
sensitivity.
The 10-2 (44-point) FDT full threshold test is a central 10 degree visual field test for use with
retinal disease (AMD, Diabetic Retinopathy) and end-stage glaucoma. The Macula
(16-point) FDT full threshold test is a central 5 degree visual field test subset of the 10-2 test.
On the left in the lower half of the full threshold test 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 from the
upper plot into shaded symbols which indicate the statistical significance of each decibel
deviation. These are explained in
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 you to read the results
like an isopter plot or graytone.
Humphrey Matrix User Manual
2048
log
10
c
Table 4-2, "Probability Level
2660021138935 Rev. F 2015-11
where c ranges
10 H
Classifications". The
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