| |||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||
Items in cart [0]
| [ Top of Page ] [ Home ] [ Contact Us ] [ Help ] [ The National Academies Home ] | ||
|
||||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||||||
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 81
CHAPTER 4
USING COLOR VISION TESTS
EVALUATION OF CONGENITAL AND ACQUIRED COLOR VISION DEFECTS
The hereditary nature of color vision disorders was recognized at the
end of the eighteenth century. In the nineteenth century there were
major disasters with loss of life in the shipping and railroad
industries. These tragedies were attributed to the failure of
engineers to recognize a colored signal.
As a result, people with
congenital red-green defects were and still are excluded from positions
as pilots or engineers in commercial air, sea, and rail transport and
similar duties in the armed forces. Tests that were developed to
evaluate color vision were both practical and empirical. While the
anomaloscope remains the only clinical method for precise diagnosis of
the presumed genetic entities, many tests have been devised for quick,
inexpensive, and efficient screening of the color-defective population
Screening tests are used to identify individuals who may eventually
require more extensive color testing. Their usef ulness is in the
identif ication of such individuals rather than the diagnosis of the
color def eat. ~ ~
of modes t cost .
.
Screening tests are easy to administer and score and are
Rapid Screening of Congenital Red-Green Color Defects
Rapid screening of red-green color defects may be necessary in the
military, schools, or transportation and other industries.
The most effective test for rapid screening is one of the validated
plate tests designed for this purpose including the Tshihara, Dvorine,
AO H-R-R, and other series of pseudoisochromatic plates that detect
about 96 percent of the cases confirmed by anomaloscoPe (Table 4-l).
It is common to rely on a single test or even on a few selected
plates. It should be noted that some normal subjects read the hidden
digits of the Ishihara test; and, of course, some normal subjects will
misread occasional plates. The deuteranomalous trichromat with good
discrimination may pass the majority of a set of plates.
We are not aware of any screening test employing colored slides of
transparencies that has been adequately validated. It is inappropriate
to attempt to make a ~home. screening test by color photography of an
81
OCR for page 82
82
TABLE 4-1 Screening for Congenital Red-Green Defects Using Plate Tests
Status
Test
Validated
Not intended for screening
Unsuitable due to
poor validation
AO Plates
AD H-R-R Plates
Dvorine
Tshihara
Tokyo Medical College
City University
Titmus Color Perception Test
Bausch and Lomb Ortho-Rater
Keystone Telebinocular
existing plate test. Color reproduction is affected by the type of
film, the illuminant used for photography, the color processing, and
the illuminant used to project the transparency. Color processing to
precise standards is very difficult. Although in the future color
screening tests may be produced using colored transparencies, any such
test will require adequate spectrophotometric control as well as
validation in the population.
Diagnosis of Red-Green Defects
Anomaloscopes may be used for diagnosis of red-green color vision
defects. The anomaloscope is the only clinical instrument for
diagnosis and classification of the presumed Genetic entities of
dichromacy and to both simple and extreme anomalous trichromacy as
defined by Franceschetti (1928). Anomaloscope examination is t~me-
consuming, and only a trained person can use the anomaloscope. The
test must include a full examination of the matching range, it is
inappropriate to allow one or two matches.
an aaa~tlona1 problem Is
that commercially available anomaloscopes are very expensive.
Plate and arrangement tests are not entirely successful at
diagnosis of congenital red-green defects. The failure of plate tests
results from the fixed color relations of figure and background. There
is sufficient variation in the color vision of defective observers that
a proton observer may fail a deutan diagnostic plate or vice versa.
Confusion axes on arrangement tests similarly may show ambiguity. The
characteristic error axis on the FM 100-hue test may not occur if the
color-defective observer makes relatively few errors.
OCR for page 83
83
Recognition of Congenital Blue-Yellow Defects and Achromatopsia
Recognition of congenital blue-yellow defects requires the use of one
or more of the tests designed for this purpose. Plates for blue-yellow
defects include the AO H-R-R, the Tokyo Medical College plates, and the
Farnsworth F: plate. Normal observers with heavy ocular pigmentation
may miss the green symbol on the F2 plate and appear to show a tritan
defect. Failure to perceive the blue symbol usually seen by normal
observers and tritans is indicative of congenital red-green defect.
The F2 plate should be used in conjunction with another test.
Recently, van Norren and Went (1981) suggested that detection of a blue
increment pulse on a yellow background provides a sensitive and
efficient test. The Farnsworth Panel D-15 and the FM-100 hue test are
important in recognition of blue-yellow defects.
Evaluation of Acquired Color Vision Defects
The detection and classification of acquired color vision defects may
be accomplished by use of an anomaloscope combined with a test that
measures chromatic discr imination. In addition, 8 to 10 percent of
males with acquired color defects have a concomitant congenital color
defect; the examiner should be alert to this possibility. Plate tests
are of variable usefulness in testing acquired color defects. An
observer with an acquired color-defect may not give the expected
reading; that is, read the numbers designed for normal or congenitally
defective observers; misreadings may occur. If an observer with
reduced visual acuity fails a plate test, the examiner cannot conclude
that there is a specific kind of color defect. Further analysis is
necessary. Arrangement tests are of particular importance in acquired
color vision defects. The Lanthony Panel D-15 and Lanthony New Color
Test were designed specif ically for evaluation of acquired color vision
defects .
CLASSIFICATION AND QUANTIFICATION
OF CHROMATIC DTSCRIMINATrVE ABILITY
In some applications it is important not only to screen for color
defects but also to classify the defect according to chromatic
discriminative ability.
Test Batteries
Many examiners decide on a test battery to fulfill their specific
requirements. Choice of a test battery reflects the testing require-
ments, the availability of tests, the personal experience of the
examiners, and the time available for testing.
e
OCR for page 84
84
An example of a test battery for congenital red-green defects is
that designed at the U.S. Naval Submarine Medical Research Laboratory
(Paulson, 1973) (Table 4-21. The battery includes the use of a set of
plates, lantern, arrangement tests, and an anomaloscope. The battery
allows recognition of congenital red-green color-defective observers
and separation of color-defective observers into four categories:
individuals showing (1) mild, (2) moderate, and (3) severe loss of
chromatic discrimination, and those showing (4) dichromatic color
vision. The mild and moderate categories tend to be predominantly
simple and extreme anomalous trichromats; the severe and dichromat
categories include individuals who are extreme anomalous trichromats
and dichromats. The correlation is not perfect since chromatic
discriminative ability varies widely among anomalous trichromats. The
NSMRL test battery will not necessarily predict the performance of the
defective observer on other color tasks (Kinney et al., 19791.
Verriest (1968b) proposed a test battery (Figure 4-1) for
evaluation of congenital defects that includes the Ishihara, F2
plate, AD H-R-R, Farnsworth Panel D-15, Lanthony Desaturated Panel
TABLE 4-2 NSMRL Test Battery for Determining Degree of Color Vision
Defect
. . .
-
Class
Pseudo- D-15 H-16
isochromatic FaLant Test Test
I. Normal
trichromatic Pans
Anomalous
trichromat
(mild defect) Fail
Pass Pass Pass
Pass Pass Pass
III. Anomalous
trichromat
{moderate
defect) Fail Fail Pass Pass
IV. Anomalous
trichromat
(severe
defect)
Fail
Fail Fail Pass
V. Dichromat Fail Fail Fail Fail
Source: Paulson (19731.
OCR for page 85
85
I. Test battery for congenital color vision defect (Verriest, 1968b)
A. Ishihara (16- or 24-plate editions)
B. F2
C. AO H-R-R
D. Farnsworth Panel D-15
E. Lanthony Desaturated Panel D-15 (if Farnsworth Panel D-15 is
normal)
F. Nagel Model I anomaloscope
II. Test battery for acquired color vision defects (Pinckers, 1978a)
A. Initial screening
1. AO H-R-R
2. Lanthony New Color Test - Box 6/4.
a. If Box 6/4 failed, do Box 6/8.
b. If Box 6/4 passed, do the Desaturated Panel.
B. Red-green defects revealed by initial screening
1. Ishihara
2. FM 100-hue
3. Nagel Model T anomaloscope
C. Blue-yellow defects revealed by initial screening
1. F2
2. FM 100-hue
3. Pickford-Nicolson
FIGURE 4-1 Test Batteries for Congenital and Acquired Color Defects
D-15, and Nagel Model 1 anomaloscope. It was suggested that the
Lanthony Desaturated Panel be used when the Farnsworth Panel D-15 gives
normal results or shows only minor errors. This battery allows good
differentiation of protanomaly, protanopia, deuteranomaly, deuteranopia,
tritan defect, and achromatopsia.
Pinckers (1978a) proposed a battery for diagnosing acquired color
vision defects in the ophthalmology clinic. This battery, also shown
in Figure 4-1, includes the AO H-R-R, Lanthony New Color test, F2
plate, Ishihara, FM 100-hue test, and both the Nagel Model I and
Pickford-Nicolson anomaloscopes. The minimal requirement for an eye
clinic should include a screening test, the Panel D-15 or Lanthony New
Color test, the FM 100-hue test, and an anomaloscope. If the screening
test does not include blue-yellow Plates, the F: plate may be added.
-
Quantification of Chromatic Discriminative Ability
Typically it is not appropriate to use the number of errors on a
screening plate test as a numerical indication of chromatic discrimina-
tive ability. Color-defective observers fail a screening plate because
-
OCR for page 86
86
to them the colors in the f igure match those of the background . Fo r
most tests, the colors in the figure and background were chosen empiri-
cally on a few "test" observers. There is considerable variation among
color-defective observers, and the optimal colors for figure and back-
ground will vary among these observers. A color-defective observer
with poor chromatic discrimination may make few errors on a screening
plate test because the color vision of his eye differs from that of the
observers on whom the test was optimized. Conversely a color-defective
observer with good chromatic discriminative ability still may fail many
of the plates if the colors happen to be optimized for his eye. The
Dvorine is one plate test for which it is specifically recommended that
the number of errors in reading the plates gives an estimate of
severity. However, we were not able to find data evaluating the class)
fication of severity on the Dvorine plates from which the statistic of
association, K, might be calculated.
The Farnsworth-Munsell 100-hue test has been used as a quantitative
test of chromatic discrimination even though its designer, Dean
Farnsworth, originally suggested only that observers could be specified
as showing superior, average, or inferior chromatic discriminative
ability. It is generally accepted that the test involves not only
chromatic discriminative ability but also cognitive parameters, such as
concentration, patience, and cooperation. It is appropriate, however,
to compare an observer's error score with a set of population norms,
and there are some cases in which it is appropriate to use the number
of errors on the FM 100-hue test in a quantitative way (see Arrangement
Tests,. in Chapter 3~.
-
SCREENTI* FOR PROFESSIONAL PURPOSES
The choice of a test is dependent on both color vision requirements and
t _ availability. It must be decided whether to choose only those
observers with good discrimination. Such decisions are important
because the exclusion of dichromats, for example, does not ensure that
all selected observers will have good color discrimination. After
careful consideration, it may become obvious that not all defective
observers need to be excluded or, alternatively, that it is unnecessary
to select only the best for the task. There are professions and skills
in which good discrimination is advantageous but in which a defect is
not an insurmountable handicap. Of course there are situations that
require good discrimination, and in these occupations it is absolutely
necessary that only those with good ability be selected. Even when
color vision requirements are known, one must consider the availability
of tests, money, and time, and whether the examiner possesses or is
willing to acquire the skills that would enable him or her to administer
validly the more complicated tests. Finally, it may be necessary to
design a field test rather than use a clinical color vision test; for
example, when an employee is required to reject a production line item
whose color differs from a standard given tolerance step.
Preliminary screening may be used to eliminate observers with
congenital defects. Because each clinical test measures a specific
OCR for page 87
87
ability, the task required of the color worker must be considered. if
the task involves the perception of small saturation differences, an
appropriate test is the Color Aptitude test. If small color differences
must be distinguished, the FM 100-hue test may be used. If the task
involves metameric matching, such as in color mixing in the textile and
or inning industries, the anomaloscope should be used.
The screening of candidates for some occupations is performed best
by means of specialized field testy that reproduce the actual
Eli hiring "n - Anti - r - ~ an the Ah
am _~ _ea __ ~_~ ~ For example, the ability to
recognize colored signals is evaluated best by a field test using
signal equipment. It is extremely important, however, that any such
field test be standardized. The same distance, illumination levels,
number of stimuli, and so on, should be used for all candidates. The
ability to sort materials by color (e.g., cotton, diamonds, pearls, and
gasolines) is evaluated best by a field trial using real materials; the
materials should be identical to those encountered in the job situation,
and the type and level of illumination must be exactly replicated.
TEST ADMINISTRATION: TRAINING PERSONNEL TO ADMINISTER TESTS
The majority of clinical color vision tests are designed for use by
personnel with minimal training in color vision testing. Instructions
are provided with many plate and arrangement tests; in most cases,
careful reading of these instructions will provide sufficient informa-
tion for correct test administration. Scoring of the FM 100-hue test
is somewhat complicated, especially when error scores are high. The
manual accompanying the test, however, provides ample instruction.
Plotting the errors is somewhat easier using the technique described by
Kinnear (1970~. Lantern tests are designed for easy administration.
The major exception among clinical tests is the anomaloscope: adminis-
tration of an anomaloscope examination requires knowledge of calorimetry
and/or extensive training in use of the instrument. Anomaloscooe exami-
nation should not be attempted by unskilled personnel. The procedures
detailed in the section on anomaloscopes in Chapter 3 must be followed.
Even when the instruction manual for a given test is understood,
there are a number of precautions that personnel must follow:
Use a standard procedure. Standardized procedures and conditions
must always be used during administration of clinical tests, such as
the FM 100-hue test, pseudoisochroma~ic plates, or the anomaloscope.
The level and type of illumination must be constant. A fixed set of
verbal instructions must be read to the observer, since variation in
instruction might bias responses._ The use of color names should be
avoided e Use of a standard procedure allows comparisons to be made
between data collected by examiners in other clinics or even by the
same examiner on different occasions. Recommended procedures for each
test are detailed in Chapter 3.
Follow scoring instructions carefully. The test must be scored
according to the instructions that accompany the test. The score sheet
should contain the following type of information:
r
OCR for page 88
88
Personal data: e.g., name, address, telephone
Birth date, sex
Testing information: date of test, illuminant (for plate and
arrangement tests), monocular (which eye) or binocular
Data relevant to testing situations: occupation, visual
acuity, etc.
For plate tests, a sample scoring sheet may be provided; if not,
one must be designed. In addition to the information above, a scoring
sheet should include a place to record the response to each plate. It
is helpful if the sheet indicates the expected responses of normal and
color-defective observers. A good score sheet indicates to the examiner
how to interpret the result.
For the anomaloscope, the examiner should note the test brightness
setting made for each mixture ratio. The examiner should also note
whether the setting was accepted as a color match and if not, why not
(for example, too much red or too much green in the mixture field).
Match the test to the ability of the observer. m e majority of
color vision tests are designed for use with observers who are not
familiar with the specific test or testing procedure. Patients or
prospective employees may be nervous about the testing situation. Thus
test results may be biased by cognitive or emotional factors. Cognitive_
factors of some tests may be beyond the capabilities of some patients, e
notably individuals with other visual, motor, or intellectual handicaps,
the elderly, and the very young. Furthermore, the majority of color
vision tests were designed for use with young adults with normal visual
acuity. Personnel administering clinical tests should be made aware of
these factors and be prepared to deal with the occasional ~difficult"
observer.
Do not allow observers to wear tinted classes or tinted contact
lenses. Color testing should not be performed on observers wearing
tinted glasses or tinted contact lenses. Tinted glasses are easily
identified. The examiner should ensure that tinted lenses are not
being worn. Tinted contact lenses may not be noticed; all observers
should be asked if they wear such correction. Some contact lens wearers
also have regular clear glasses. In this case, an appointment should
be made for a future date, and the observer should be told to wear the
glasses rather than the contact lenses.
The majority of screening tests can in fact be performed with
glasses or contact lenses removed. Spherical refractive errors of two
or three diopters should not cause difficulties for screening plates if
the patient is myopic or is hyperopic with adequate accommodative
ability. Refractive error of myopes is often reduced on first removing
the hard contact lens. If necessary, an observer may use a hand-held
ophthalmic lens for screening plates or ophthalmic trial frames for
arrangement tests. The Nagel Model I and Neitz anomaloscopes have
adjustments for focus.
OCR for page 89
89
Decide whether to use monocular or binocular testing. Few manuals
specify whether testing should be monocular or binocular. In research
it is customary to test one eye at a time. In the eye clinic, it is
especially important to check each eve separately, since eye diseases
mat affect the eyes to a different degree. On the other hand, routine
screening as performed in schools or in the military is usually
performed binocularly.
What to do when tests given different results: Occasionally an
observer will fail one set of screening plates and pass another set.
Alternatively, an observer may show a defect on screening plates but
not on the anomaloscope or vice versa. If any set of screening plates
is failed the observer is considered to have a color defect. An
anomaloscope examination is required to provide further classification
of the defect. Observers who show this behavior include anomalous
trichromats with good chromatic discrimination. These individuals are
called minimale anomalen (Pokorny et al., 1979~. Additionally some
normal trichromats may show minor color abnormalities (Pokorny et al.,
19797. The majority of normal trichromats with minor color defect show
generally poor color discrimination and will not only fail color
screening tests but show abnormal error accumulations on discrimination
tests. Rarely, normal trichromats will fail a screening test but show
no other sign of color defect.
SOME SPECIAL PROBLEMS OF TESTING
Color vision tests were designed by adults for use with adults with
normal visual acuity. Some adults (e.g., illiterates, observers not
fluent in the examiner's language, or the elderly J may present the
examiner with special problems. Testing of children also requires
special attention. The testing of a suspected malingerer or concealer
also may present problems. The general rule is to use common sense and
to perform a test only if it is clear (1) that the observer understands
the procedure, and (2) that the test can be performed using appropriate
techniques.
Testing Illiterates
Illiteracy is relatively rare in countries with compulsory grade-level
education. Illiteracy, however, may be encountered in less-developed
countries, especially by researchers interested in genetic studies.
The problem of illiteracy may then be compounded by language
difficulties. If some mutual understanding is reached, tracing of
screening plates is still appropriate.
The Ishihara test includes tracing patterns for illiterates; the
symbols on the AO H-R-R may be traced with a brush, as may the numerals
on the other plate tents. Anomaloscope examination may prove difficult
unless the observer understands the task.
OCR for page 90
so
Language Problems
Examination of adults not fluent in the examiner's language may be
difficult if no translator is available . With good will and by mimicry
and sign language, a foreign-speaking individual may be tested on
screening plates. The observer should either trace the symbols with a
brush or write down the symbol or numeral on an adjacent piece of
blank paper (not the score sheet). Alternatively a matching technique
may be used in which drawn or cutout outlines of the figures are
prepared for the observer to point at or superimpose on the plate.
Arrangement tests and anomaloscope examination require a better level
of communication.
Testing the Elderly
With respect and consideration, the elderly individual should offer no
problems in testing. The arrangement tests may be difficult for
individuals with poor manual dexterity, such as those with arthritis.
Such individuals may drop the chips and become embarrassed or impatient
with the task. Again the solution is common sense. Perform only those
tests that are necessary for diagnosis and that are within the patient's
abil ity .
Bifocal prescriptions may offer a problem in anomaloscope testing.
The observer may have trouble finding the field in the telescope view
of the Nagel anomaloscope or may wonder which part of the bifocal to
use. The observer should always look through the part of the bifocal
lens that is intended for distance use, usually the upper half of the
lens. In some cases, removing the glasses and using the telescope
adjustment may be all that is needed. In ether cases, the observer may
prefer a hand-held ophthalmic trial lens of the appropriate power for
distance vision rather than the regular glasses. It is important to
ensure that the dividing line of the split field appears clear. The
Pickford-Nicolson anomaloscope should offer fewer difficulties to
bifocal wearers.
Testing Children
Children under 12 years of age offer special problems in color testing,
since many of the tests require intellectual abilities that develop at
different ages: screening tests require knowledge of the alphabet or
numerals; arrangement tests require the concept of serial ordering.
The situation is even more difficult in the case of retarded children.
With increased use of color coding in school materials, it is of
growing importance to identify congenital color defects in young
children. Many observers with a congenital color defect retain
memories of being treated as ~stupid. or ~troublemakers. because they
had difficulties making color discriminations that were immediately
evident to color-normal observers (Sloan, 1963~. Color tests may also
be.helpful in identifying hereditary retinal disease in children.
OCR for page 91
91
There are three tests designed especially for children: the Guy's
Hospital color vision test,* the Matsubara test,** and the Titmus
pediatric color perception test. The Guy's Hospital color vision test
contains design flaws that make it ambiguous and confusing to adults,
and thus presumably equally confusing to children (Alexander, 1975~.
The Matsubara test contains symbols of items that are familiar and
important in Japanese culture (e.g., cherry blossoms) but that are not
necessarily familiar to American children. To date, none of these
tests has received full validation in an American population.
Although a review of the literature revealed rather variable results
in testing young children (Alexander, 1975; Verriest, 1981), it is
possible to test children successfully with the adult tests, such as
the AO H-R-R and the Ishihara screening tests. Care is needed to match
the task to the age, attention span, and intellectual development of
the child. It is important to give careful instruction to ensure that
the child understands what he or she is asked to do. Such instruction
should not contain reference to color names or color differences that
the color-defective child may not understand. By their very nature,
color tests are frustrating and difficult for color-defective observers,
and this point must be remembered when dealing with color-defective
children.
Pre-school and Kindergarten Children (3 to 5 Years old). Today
with increased use of pre-schools and educational television, many
children of 3 to 5 years know alphabet letters, the numerals from 1 to
10, and simple geometric shapes, as well as the concept of "same" and
"different. "
Young children may be tested with the AO H-~-R test (Alexander,
1975~. If necessary, the examiner may draw the three symbols--triangle,
circle, and cross--on a sheet of paper and ask the child "Do you see
any of these shapes on the color plate?. If the child says eyes n he or
she is asked to point first to the quadrant of the plate in which the
child sees the symbol and then to the symbol on the sheet of paper that
matches the symol seen on the plate. It is important to practice the
procedure with the demonstration plates and to muke certain that the
child distinguishes the three geometric shapes.
The AO H-~-R is preferable to the Ishihara or Dvorine with young
children even if they know some numerals, since many children of this
age will confuse certain numerals and will not be sure how to identify
a double-digit numeral. For example, when shown a plate containing the
numeral .26,. the child may say .6. or .2. or even .9~ not knowing that
the numeral is called Twenty-six. The alternative of using the
tracing patterns designed for illiterates is not optimal, since few
*The Guy's Colour Vision Test for Young Children by Peter A. Gardiner,
M.D.
**Colour Vision Test Plates for the Infants, originated by Hiro
Matsubara and revised by Koku Kojima. Tokyo, Handaya Co., Ltd.
OCR for page 92
92
young children have the necessary manual dexterity to perform an
accurate tracing.
.
First- and Second-Grade Children (6 to 8 Years old). Many children
of 6 to 8 years can perform the screening tests. However, few children
in this age range understand the concept of serial ordering or have the
attention span necessary to complete a serial ordering test such as the
Panel D-15 (Adams et al., 1975; Cohen, 1976~. A 6-year-old may start
the Farnsworth Panel D-15 correctly and make minor errors after a few
caps, or may put two favorite colors together.
In addition to the plate tests, a limited amount of information may
be obtained from 6- to 8-year-olds on an anomaloscope. The Pickford-
Nicolson anomaloscope has the advantage that both child and examiner
can point to one or the other side of the vertically split field,
thereby eliminating the need to describe what is seen. The Nagel
anomaloscope has a disadvantage in that some children have difficulty
aligning themselves to see the field in the telescope view. The
examiner should set both the color mixture and brightness and ask the
child, Ado you see a circle of color, or can you tell that there are
two colors in the circle?. The examiner must present matches that have
an obvious brightness difference (green primary and yellow turned dim),
matches that are representative of a normal trichromat, and matches of
the common red-green defects.
~ . Children of 8
to 11 years can usually perform the screening tests and the Farnsworth
Panel D-15. They will perform on the anomaloscope If the examiner sets
the color mixture and watches carefully how the child sets the yellow
brightness; the examiner should set it also, if necessary. Children of
8 to 11 years can perform the FM 100-hue test; however, many become
bored after one or two boxes, with a consequent performance decrement.
Mentally Retarded. Plate tests are not suitable for screening in
the mentally retarded population. Color screening of mentally retarded
boys (with plate tests) revealed a high failure rate (20 to 30%} with
poor inter-test correlations (Salvia 1969; Salvia and Ysseldyke,
1971a, 1971b; 19721. The high rates represent failure of screening
plates by mentally retarded boys with normal color vision defined by
anomaloscope. The problems are evident in AD H-R-R, Dvorine, and
Ishihara. Arrangement tests, such as the FM 100-hue test and Farnsworth
Panel D-15 (Salvia, 1969), also offer difficulties and may reveal high
incidences of apparent color defect. Salvia and Ysseldyke (1971a,b)
report an incidence of 8.7 percent for congenital red-green color
defects when the Pickford-Nicolson anomaloscope was used. If the
examiner is confident that the mentally retarded individual understands
the anomaloscope test, this test may be used for evaluation of color
vision in the mentally retarded population.
e
OCR for page 93
93
Malingering and Concealing
Two contingencies that arise occasionally include the person with
normal color vision who claims to have a color vision defect (either by
malingering or-due to hysteria) and the person with a congenital vision
defect who wants to pass a color vision test (concealment). The
malingerer is the more difficult to detect.
Malingering and Hysteria. Malingering can occur in connection with
the assessment of workmen's compensation after an industrial accident.
Hysteria reflects a psychosomatic basis. It can be difficult to detect
malingering and hysteria. One way of revealing malingering or hysteria
is by use of tests such as visual fields and electroretinography.
Generally a battery of tests is used, in which case the observer tends
to produce atypical or contradictory results.
The malingerer may claim that he is unable to read any of the
pseudoisochromatic plates, including the demonstration plates. If
visual acuity is good, failure of the demonstration plates is indicative
of malingering or hysteria. On tests such as the Panel D-15 or the FM
100-hue test, the malingerer will arrange the samples haphazardly.
High error scores of 400 or more without predominant axis in an adult
with normal visual acuity are indicative of malingering. The
malingerer gives inconsistent answers on anomaloscope examination.
Acceptance of H impossible matches by an adult is indicative of
· .
malingering.
The most difficult cases occur when malingering or hysteria is
superimposed on a preexisting congenital or acquired color vision
defect (Kalberer, 1971; Pickford, 19721. A comparison of the color
vision test results with other visual functions such as visual acuity,
dark adaptation, and visual field, may be necessary.
Concealing. A person who deliberately tries to conceal a congenital
color vision defect usually wants to be accepted for a job in which
normal color vision is a prerequisite, such as in shipping or air
transport. That person may have a good chance if the correct answers
to a set of screening plates are provided and learned in advance
(Perdriel et al., 1975; Verriest and Hermans, 1975~. Some defective
observers may use tinted glasses or tinted contact lens (e.g., the
X-chrom lens) to read pseudoisochromatic plates. It is difficult or
impossible to conceal successfully on a properly administered
anomaloscope test.
COLOR VISION ~CURES. AND ~REMEDTES.
Many cures and remedies for red-green color vision defects have been
reported in the newspapers, in lay magazines, and even in professional
journals. Attempts to cure color vision defects reached a peak during
World War II because of the number of young men with red-green color
defects who were eager to be accepted into the Navy, Air Force, and
office training programs. Some of the alleged cures and remedies, none
OCR for page 94
94
of which proved to be successful under control investigation, included
warming one eye; staring at flashing red and green lights; wearing
colored goggles; being coached in color naming and color matching; and
taking injections of iodine, staggering doses of various vitamins , and
injections-of extracts from cobra venom, marigolds and lobsters. A
two-volume book for testing and training color-defective observers,
which was published in 1944, claimed that people with color vision
defects were merely visually confused and needed to identify their
confusion and then correct it by training. Other reports described
color-defective observers who were able to pass the color vision test
for the military after extensive training on the test.
In 1946 the Army-Navy National Research Council Vis ion Committee
r equested from the American Committee on optics and Visual Physiology
(ACOVP) a statement of the efficacy of corrective training . The
statement was adopted by the American Academy of Ophthalmology and
Otolaryogology, the American Ophthalmological Association, the Section
on Ophthalmology of the American Medical Association, and the
Association of Schools and Colleges of Optometry. Its conclusions are
still valid: No method had been found for the correction of color
blindness, whether called 'color weakness,' 'color confusion,' or
'color defectiveness.' Men can be coached to pass tests, but their
physiologic deficiency cannot be repaired. Any claims to the contrary,
any treatment which convinces operators that they can see colors they ~
could not see before will decrease safety in transportation, decrease
security in national defense, and decrease efficiency in industry.
(quoted in Farnsworth and Berens, 1948~.
Since that time, several other techniques for improving color
vision have been proposed. One of them involves wearing a color
filter, in the form of a contact lens, over one eye. With the use of
this lens, which is called the X-chrom lens, the two eyes receive
different spectral distributions of light. Because of the relative
changes in lightness that the filter produces, the lens may help the
color-defective observer to make chromatic discriminations and to pass
some color vision tents. However, neither the X-chrom lens nor any of
the other color vision cures and remedies that have been proposed can
restore normal color vision function.
The working group is aware of no scientific study demonstrating
that performance of complex real work tasks by people with defective
color vision would be enhanced by use of the X-chrom lens. Siegel
(1981) has discussed hazards potentially associated with use of the
X-chrom lens for tasks such an automobile driving. ACOVP has
recommended that examiners be extremely cautious in deciding whether to
allow persons to use such devices when being tested for color vision
required for occupations (quoted in Siegel, 1981~.
e
Representative terms from entire chapter:
pass pass pass