Threshold Tests - Zeiss Humphrey matrix User Manual

tests in the Humphrey FDT and Humphrey Matrix Visual Field Instruments so the tests are
comparable between the two instruments. Each test location is assigned one of four probability
levels, depending on the test selected. Each visual field location is tested until the patient
responds, or until all three probability levels are tested. The initial probability level is tested twice
if needed, followed by once at each of the other levels to complete the N-30 screening. As a
result, the screening test time will increase for patients with eye disease.
The 24-2-5 (or 24-2-1) FDT screening test is a screening version of the 24-2 full threshold test.
Each test location is assigned one of two probability levels, depending on the test selected. Each
visual field location is tested at a single probability level (pass/fail). Each visual field location is
tested until the patient responds or the location is tested twice at the initial probability level to
complete the 24-2 screening.

THRESHOLD TESTS

All the Humphrey Matrix visual field threshold tests are full threshold tests meaning that they
provide quantitative measures of the visual function at each location tested. The threshold test
results consist of a raw threshold plot (dB values), a gray scale plot (pattern shading), total and
pattern deviation plots (dB values), total and pattern deviation probability plots (pattern shading),
MD and PSD global indices (numeric with probability values), overall reliability measures, along
with patient and test information for each eye tested. The probability plots indicate one of five
possible probability levels with different patterns, increasing in darkness with decreasing
probability level. Refer to the sample printouts included at the end of this User's Guide.
The N-30-F FDT full threshold test is essentially the same 19-point full threshold test performed
on the Humphrey FDT Visual Field Instrument, except that moving the fixation target is not
required and the threshold algorithm has been optimized to reduce test time with the Humphrey
Matrix. The same normative database is used for the N-30 tests in the Humphrey FDT and
Humphrey Matrix Visual Field Instruments so the tests are comparable between the two
instruments.
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
(maximum contrast) and H is approximately 2. Note that XX dB 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 Humphrey Field
Analyzer values.
The 24-2, 30-2, 10-2 and Macula FDT full threshold tests are modeled after the Humphrey
Field Analyzer tests to provide visual field test results that are familiar to you. 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 a
ZEST (Zippy Estimate of Sequential Testing) to provide accurate threshold results as quickly as
Humphrey Matrix Visual Field Instrument
Rev. D 08/21/06 PN 701692
2048
⎛ ⎞
× × ×
where c ranges from 1 (minimum contrast) to 2048
log 10 H
⎝ ⎠
10
c
17