HRR 4th Edition Technical Article
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The original HRR was
developed by LeGrand Hardy, M.D., Gertrude Rand, Ph.D. and M. Catherine
Rittler, B.A. to serve a threefold purpose: (1) as a screening test to
separate those with defective color vision from those with normal color
vision, (2) as a qualitative diagnostic test to classify the type of color
defect (whether protan or deutan, tritan or tetartan), and (3)
as a quantitative test to indicate the degree of any defective color
vision (whether mild, medium or strong).
This chart shows the Chromaticities of the
first three HRR Editions and their fit or deviation from the co-punctal
lines.
The screening goal of the test has consistently been achieved,
however, weaknesses
in the first three editions in diagnostic classification as to type and
extent were discovered in previous critical evaluations (e.g., Walls,
1959).
The
purpose of the reengineering effort of fourth edition of the HRR test has
been to 1.) correct these imperfections 2.)
update to incorporate the latest learning in color vision including
genetics and 3.) apply state-of-the-art printing methods to produce a
color test of unsurpassed quality. Previous analysis of the earlier
editions indicated that
the chromaticities were not as close as desired to the original
target dichromatic confusion lines (see figures A and B). Further,
development over the past 20 years has indicated that the deutan
confusion line is more accurately plotted as 1.40, -0.40 rather than
1.08, -0.08 used in the development of the original HRR. For this 4th printing,
variables were eliminated by early standardization of paper for the
4th Edition
and a CIE Lighting Source (Richmond HRR Illuminator P/N 1339). A
single color was selected for the gray background dots of all the
plates (x=0.31, y=0.32). This
point plus the co-punctal points defined the target confusion lines
on which all colors in the plates must fall.
In order to improve qualitative results, specific deutan
points were corrected. The largest correction was a change in x and
y of -0.0359 and –0.0055 respectively for the deutan symbol in
plate 16. Inks were then formulated and tested for the 4th Edition
that more closely matched the dichromatic confusion lines (see
figure C). Final color selections were then verified with known
subjects in a clinical setting. Administration of the test and the
HRR score sheet are unchanged when using this new 4th Edition.
The results achieved are shown in the HRR 4th Edition
Chromaticities Plot shown on page 2.
In
addition to these capabilities, the HRR was designed very cleverly
to increase test validity by eliminating scoring variability. The
Ishihara, for example has historically been an excellent test for
congenital defects, however, determination
can be difficult. The 38 plate edition states: "If 17 or more
plates are read normally, the color vision is regarded as normal.
If only 13 or less plates are read normal, the color vision is
regarded as deficient.". This leaves determination of 16 to 14 errors
undetermined. Clinical testing of the HRR 4th Edition
has provided clear determination in detection, classification, and
estimating the degree of defective color vision with better than 99%
of the participants.
The colors in each of the HRR
test figures have been plotted to determine their alignment with the
colors required. This HRR 4th Edition Final Chromaticities Plot shows
how closely this recent printing matches the colors required as
determined by the dichromate line
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