Chapter 12. Visual System Rating Steps
The individual should be tested with the best available
refractive correction (281, 283).
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Part 1. Visual Acuity Score (VAS)
Test each eye for visual acuity using a standard letter
chart and record the results in US notation in Table
12-3 (284).
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Visual Acuity Score (VAS) Both Eyes (OU)
Test the binocular vision for visual acuity using a
standard letter chart and record the results in US
notation in Table 12-3 (284).
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Visual Acuity Scores (VAS)
Determine the visual acuity score for each eye and for
binocular vision from Table 12-2 (284) (fifth column in
table) and record in Table 12-3 (284).
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Functional Acuity Score (FAS)
The FAC is computed by multiplying binocular visual
acuity (VASOU) by 3 then add the three scores and
divide by 5 to get the functional acuity score (FAC).
Record in Table 12-3 (284).
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Impairment Due to Visual Acuity
Assuming visual acuity is the only deficit then
impairment is determined by subtracting the functional
acuity score (FAS) from 100. Table 12-4 (285)
Impairment = 100 – FAS
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Part 2. Field Vision - Field Radius Angle
Field is measured in terms of the field radius angle.
The field radius angle is the angle away from fixation
that an object can be seen. The larger the angle the
better the visual field (the wider the cone of vision).
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Central Field of Vision
The central field of vision is the vision within the
radius of 10º, shown by the circle in Figure 12-1 (288).
The field of vision within the central field of vision is
given more value than the outer field of vision.
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Outer Field of Vision
The outer field of vision is the vision field from the
radius of 10º to 60º.
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Field Vision - Testing Equipment
Testing can be done with the Goldmann isopter. This
produces a continuous graph called isopter of the
largest radius angles throughout the 360º field of
vision.
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Visual Field Impairment – Meridians
The calculation of impairment needs the radius values
along meridians. Meridians are lines extending from
center at 25º, 65º, 115º, 155º, 195º, 225º, 285º, 315º,
and 345º. Figure 12-1 (288)
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Overlay Grid of Meridians
The Goldmann graph does not have meridian lines
marked. The grid of meridians must be overlaid or
drawn on the Goldmann graph.
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Radius Angles are Read from the Goldmann Graph
Values are read at the intersection of the isopter
graph and a meridian. Values within 10º radius are
rounded to the nearest 2º. Values outside 10º are
rounded to the nearest 10º.
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Visual Field – Note on Angles
The field radius is an angle and location of a meridian
line is also an angle. On the graph the field radius is
indicated as a point on a meridian away from fixation
or center of the graph.
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The Score of Each Meridian – Method I
The value from the isopter graph along a meridian is
used to determine the score for that meridian. To
convert an isopter radius angle to meridian score use
the upper part of Table 12-8 (290).
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Visual Field Score (VFS)
The scores for all the meridians are totaled to get the
visual field score. See Example 12-6.
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Visual Field Score – Subtract for Scotomata
Where there are scotomata the extent of the
scotomata along each meridian is subtracted. The
extent is the upper radius angle of the scotomata
minus the lower radius angle.
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Visual Field Score – Subtract for Scotomata
(continued)
Where the scotoma extends into the central field, the
extent within 10º is determined by using the middle
part of Table 12-8 (290) to get the subtracting score.
Example 12-8 (293).
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Visual Field Score – Subtract for Scotomata
(continued)
Where the scotoma extends into the outer field, the
amount of the extent in the outer field determines the
subtracting score. The lower part of Table 12-8 (290)
gives the values to use. Example 12-8 (293).
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Test the Other Eye
Test the other eye and calculate the visual field score
for each eye.
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Binocular Field Score
The binocular field is determined by superimposing
the graph for each eye. The binocular score is
determined as described about except that areas
seen by either eye are counted as seen; only areas
not seen by either eye are counted as defects.
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Functional Field Score - Calculating
The functional field score (FFS) is calculated by
combining the visual field scores as in Table 12-6
(289) using the formula:
FFS = (3 x VFSOU + VFSOD + VFSOS) / 5
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Visual Field Impairment
Impairment = 100 - FFS
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Visual Field Score - Method II – Count-the-Grid-Points
Count-the-grid-points method is an alternate way to
determine the visual field score.
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Count-the-Grid-Points Method
Radius grid points are drawn as dots on each
meridian at 1º, 3º, 5º, 7º, 9º, 15º, 35º, 45º, 55º, and 65º.
The grid points within the isopter graph are counted.
Grid points within scotomata are not counted.
Examples 12-7 (292) and 12-8 (293).
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Count-the-Grid-Points Method (continued)
The total grid points for all meridians is the visual field
score (VFS) for that eye.
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Count-the-Grid-Points Method (continued)
The functional field score (FFS) is calculated the
same for the count-the-grid-points method by
combining the visual field scores as in Table 12-6
(289) using the formula:
FFS = (3 x VFSOU + VFSOD + VFSOS) / 5
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Part 3. Functional Vision Score (FVS)
To get the overall impairment the acuity and field
impairments are combined. Section 12.4a. The
combining formula is:
FVS = (FAS x FFS) / 100
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Functional Vision Score (FVS) - a Note
Note that the functional scores are used in the
formula and not the impairment percentages. For
values of FAS and FFS greater than 100, use 100 in
the formula.
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Correction for Point-of-Fixation Field Loss
If the scotomata covers the point of fixation and there
is visual acuity loss then some or all of the central
field loss is ignored. Section 12.4a.3 (296)
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Correction for Point-of-Fixation Field Loss (continued)
If there is point-of-fixation field loss and the visual
acuity loss is greater that the visual field loss then the
functional field score is set to 100 (ignored). Example
12-14 (299)
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Correction for Point-of-Fixation Field Loss (continued)
If there is no vision (NLP) in one eye then the field
score is set to 100. Example 12-12 (298)
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Correction for Point-of-Fixation Field Loss (continued)
The central field loss is ignored depending of the
visual acuity score in accordance with Table 12-9
(297). This increases the function field score (FFS) in
the functional vision score (FVS) formula. Example
12-15 (300)
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Correction for Point-of-Fixation Field Loss (continued)
The point-of-fixation field loss correction is only
applied to the central field. Radius points at 1º, 3º, 5º,
7º, and 9º on a meridian. Table 12-9 (297) Example
12-15 (300)
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Further Adjustments
The FVS can be decreased by up to 15 points as
discussed in Section 12.4b (297) for contrast
sensitivity, glare sensitivity, color vision defects and
other defects.
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Part 4. Whole Person Impairment
To convert functional visual scores to whole person
impairment use Table 12-10 (298) or use the formulas
in the next frame.
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Whole Person Impairment – Conversion Formulas
FVS > 50
FVS ≤ 50 and ≥ 31
FVS ≤ 30 and ≥ 11
FVS ≤ 10
WPI = 100 – FVS
WPI = 50 + (50 – FVS) x 11/19
WPI = 62 + (30 – FVS) x 11/19
WPI = 74 + (10 – FVS) x 1.1
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