The test measures the central 24 to 30 degrees of the visual field; that is, the area
measuring 24 to 30 degrees around the point of fixation.
The Humphrey Field Analyzer central 30-2 threshold test (HFA 30-2) and central 24-2
threshold test (HFA 24-2) are tests that can meet these criteria. The HFA 30-2 tests
76 points in the central 30 degrees of the visual field. The HFA 24-2 tests 54 points
in the central 24 to 30 degrees of the visual field. For both of these tests, the
tested points are spaced in an equidistant grid pattern, with each point 6 degrees
apart horizontally or vertically from any adjacent point. Therefore, we consider the
HFA 30-2 and the HFA 24-2 to be acceptable tests when performed using a size III white
stimulus on a 31.5 asb white background.
The following examples of dB printouts illustrate the grid patterns used for the HFA
30-2 and the HFA 24-2 and provide information for interpreting the test results.
Example 1 — An HFA 30-2 dB printout for the right eye
Example 2 — An HFA 30-2 dB printout for the left eye
Example 3 — An HFA 24-2 dB printout for the right eye
Example 4 — An HFA 24-2 dB printout for the left eye
We will not use automated static threshold perimetry test results to evaluate the
visual field loss if the test was not performed using all of our requirements; for
example, a stimulus other than a size III stimulus was used, or the stimulus was not
white.
Step 2 — Are the test results reliable?
Each perimeter manufacturer will identify factors that are used to determine whether
the test results are reliable.
For the Humphrey Field Analyzer, the reliability factors are fixation losses, false positive errors, and false negative errors. Information about these factors is at the top of the chart (see Exhibits 1 and 2).
The test results are not reliable for evaluating visual field loss if the fixation
losses exceed 20 percent, or if the false positive errors or false negative errors
exceed 33 percent.
Even when the reliability factors are within the manufacturer’s specifications, we
will not use the test results to evaluate visual field loss if there is other information
in the case file that suggests that the results are not valid; for example, the test
results are inconsistent with the clinical findings or the individual’s daily activities.
Step 3 — Does the individual have visual field loss?
For acceptable tests performed on a Humphrey Field Analyzer, an MD equal to or greater
than -5 dB (for example, -4.39, -2.58, or 0) indicates that the visual field is normal.
An MD less than -5 dB (for example, -5.5, -8.85, or -11.18) indicates the individual
has visual field loss.
Step 4 — Do the test results show statutory blindness based on visual field loss?
In automated static threshold perimetry, the intensity of the stimulus varies. We
measure the extent of visual field loss by determining the portion of the visual field
in which the individual can see a white III4e stimulus. The “III” refers to the standard
Goldmann test stimulus size III. The “4e” refers to the standard Goldmann filters
used to determine the intensity of the stimulus. Therefore, a determination is needed
as to the dB threshold level that corresponds to a 4e intensity for the particular
perimeter being used. Points that are at this dB threshold level or above are considered
seeing points because they are the same intensity or dimmer than a 4e stimulus. Points
that are below this dB threshold level are considered non-seeing points because they
are brighter than a 4e stimulus.
For acceptable tests performed on a Humphrey Field Analyzer, a 10 dB threshold is
equivalent to a 4e intensity. Therefore, for these tests we consider any point with
a threshold of 10 dB or higher to be a seeing point; we consider any point with a
threshold of less than 10 dB to be a non-seeing point (see sections 2.00A6a(vii) and
102.00A6a(vii) of the listings).
After we determine the dB threshold that is comparable to a 4e stimulus, we use the
dB printout to determine whether the widest diameter of the field is less than or
equal to 20 degrees. The diameter must go through the point of fixation.
To determine whether the widest diameter is greater than 20 degrees, we may map the
visual field on a copy of the dB printout by drawing a line, which we refer to as
a pseudoisopter, midway between the seeing and non-seeing points.^{[7]} For example, for acceptable tests performed on a Humphrey Field Analyzer, we draw
the pseudoisopter between any two adjacent tested points when one threshold is 10
dB or greater and the other threshold is less than 10 dB. If any number at the outermost
edge of the field is a seeing point, we draw the pseudoisopter on the edge of the
field at that point. If more than one number is shown for a particular point, we use
the higher number to determine whether the point is a seeing point. We include the
map of the visual field in the case record.
The pseudoisopter(s) differentiates the seeing area of the visual field from the non-seeing
area. We consider the pseudoisopter itself to be part of the seeing area.
We determine whether the widest diameter is greater than 20 degrees by using the hash
marks on the horizontal (x-) and vertical (y-) axes of the Humphrey Field Analyzer
dB printout or by calculating the distance between the points. As shown above, for
the HFA 30-2 and the HFA 24-2, each hash mark covers a distance of 10 degrees, and
the degrees are divided evenly between the hash marks. Additionally, each tested point
on a dB printout from an HFA 30-2 or an HFA 24-2 is 6 degrees apart horizontally or
vertically from any adjacent tested point. The four tested points immediately surrounding
the point of fixation are each 3 degrees horizontally and vertically from the point
of fixation. Any tested point adjacent to an axis is 3 degrees from that axis.
When we measure the widest diameter of the visual field, we subtract the length of
any scotoma (non-seeing area), other than the “normal” blind spot^{[8]} , from the overall length of any diameter on which it falls. (On some Humphrey Field
Analyzer dB printouts, the normal blind spot is identified by a small triangle, as
shown in Example 1.) As previously noted, we consider the pseudoisopter to be a seeing
area and do not subtract it from the overall length of the diameter.
We will determine that the individual has statutory blindness if the widest diameter
in the better eye is less than or equal to 20 degrees, this finding is consistent
with the other evidence in the case record, and for title II, a medically determinable
impairment that could result in the visual field loss has been identified.
Examples of how we determine whether the individual has statutory blindness based
on visual field loss.
Example 5 — An HFA 30-2 dB printout for the right eye
To measure the widest diameter, we create a pseudoisopter by drawing a line midway
between points with a threshold of 10 dB and higher and adjacent points with a threshold
less than 10 dB, or by drawing the pseudoisopter on the edge of the tested area when
the thresholds at the outermost points are 10 dB or higher. As all of the outermost
points on the dB printout above are 10 dB or higher, we draw the pseudoisopter delineating
the outer edge of the visual field around the tested area.
After determining the outer edge of the seeing area as shown on the dB printout, we
need to determine whether there are any scotomata; that is, blind spots. If so, we
map the scotomata as we do not consider them when we determine whether the widest
diameter of the visual field is greater than 20 degrees. A scotoma is illustrated
below.
As all of the thresholds in the lower left quadrant of this dB printout are higher
than 10 dB, we consider this entire quadrant to be a seeing area. Any diameter that
is drawn through this quadrant will be at least 30 degrees long. Therefore, without
calculating the actual length of the widest diameter shown on the dB printout, we
can determine that the widest diameter of this visual field must be greater than 20
degrees and that this individual does not have statutory blindness based on visual
field loss.
Although we did not need to calculate the widest diameter for this example, the widest
diameter shown on this dB printout is 54 degrees on both axes. On the y-axis, the
diameter extends from the top of the dB printout to the bottom of the dB printout,
which is 60 degrees in length. However, there is a segment of the y-axis that is in
the scotoma, the segment from 6 degrees to 12 degrees.^{[9]} This segment is 6 degrees long (calculated on the y-axis by adding the 3 degrees
above the non-seeing point to the 3 degrees below it). We subtract the 6 degrees from
the 60 degrees for a total diameter of 54 degrees.
On the x-axis, the diameter extends from one side of the dB printout to the other
side of the dB printout, which is 60 degrees in length. However, there is a segment
of the x-axis that is in the scotoma, the segment from 12 degrees to 18 degrees.^{[10]} This segment is 6 degrees long. We subtract the 6 degrees from the 60 degrees for
a diameter of 54 degrees.
Example 6 — An HFA 30-2 dB printout for the left eye
To measure the widest diameter, we create a pseudoisopter by drawing a line midway
between points with a threshold of 10 dB and higher and adjacent points with a threshold
less than 10 dB.
The widest diameter is 24 degrees on the y-axis. We can determine that the individual
does not have statutory blindness based on visual field loss because the widest diameter
is greater than 20 degrees.
Example 7 — An HFA 24-2 dB printout for the right eye
To measure the widest diameter, we create a pseudoisopter by drawing a line midway
between points with a threshold of 10 dB or higher and adjacent points with a threshold
less than 10 dB.
The widest diameter is shown below.
The widest diameter is on a diagonal; therefore, we calculate its length as the hypotenuse
of a right triangle.^{[11]} The widest diameter extends from the point in the field that is 6 degrees above and
12 degrees to the left of the point of fixation, through the point of fixation, to
the point in the field that is 3 degrees below and 6 degrees to the right of the point
of fixation. These two points are 9 degrees apart vertically and 18 degrees apart
horizontally, as shown below.
To measure the widest diameter, we apply the formula for calculating the length of
the hypotenuse of a right triangle as follows: 9^{2 }+ 18^{2 }= 81 + 324 = 405. The widest diameter is the square root of 405, or 20.12 degrees,
which we round to 20 degrees.^{[12]} Assuming that this is the individual’s better eye, that the field shown is consistent
with the other evidence in file, and for a title II claim, that there is a medically
determinable impairment that could cause this field loss, we will find that the individual
has statutory blindness.
Step 5 — How do we evaluate severe visual field loss that has not resulted in statutory
blindness?
If the individual’s visual disorder has resulted in severe visual field loss but has
not resulted in statutory blindness, we will consider whether the visual disorder
meets listing 2.03B or 102.03B. A visual disorder meets listing 2.03B or 102.03B when
the MD for the better eye, measured with an HFA 30-2, is -22 dB or worse.^{[13]} If the visual disorder does not meet a listing, we will determine whether the visual
disorder medically equals a listing or, if not, assess the limitations imposed by
the visual disorder.
Exhibit 1 — Standard Chart from an HFA 30-2
Exhibit 2 — Standard Chart from an HFA 24-2
EFFECTIVE DATE: This Ruling is effective July 31, 2007.
CROSS-REFERENCES: DI 34001.012 and DI 34005.102.