1. health and fitness
2. disease

VOLUME 60, NUMBER 8
JOURNAL OF TIHE OPTICAL SOCIETY OF AMERICA
AUGUST 1970
Similarities between Congenital Tritan Defects and Dominant Optic-Nerve
Atrophy: Coincidence or Identity?*
ALEXE. KRILL,VIVIANNEC. SMITH,ANDJOELPOKORNY
Eye Research Laboratories, The University of Chicago, Chicago, Illinois 60637
(Received 2 January, 1970)
Dominant inherited optic atrophy is usually a stationary disorder with typical findings of optic-nerve
pallor, abnormal distance acuity but essentially normal reading vision, minimal visual-field defect, and
characteristic color confusions in the blue-green region of the spectrum. The severity of these is extremely
variable, even within the same family. In patients with minimal disease, distance acuity may be close to
normal and optic pallor may be so subtle that a definitive diagnosis cannot be made unless several affected
members of a family are seen. An evaluation of ocular- and color-vision findings are presented for three
pedigrees. Color tests included determination of the Rayleigh equation, the American Optical HRR plates,
the Farnsworth-Munsell 100-hue test, and determination of netural points and chromaticity confusions.
Our results suggest a strong similarity in color vision between previously reported congenital tritan defects
and patients with dominantly inherited optic atrophy. Criteria distinguishing the two conditions are suggested. However, a perusal of the literature reveals that most congenital tritanopes were not adequately
evaluated to rule out dominantly inherited optic atrophy. Therefore, the almost identical color-vision profiles
and pattern of inheritance of the two conditions lead us to question the existence of congenital tritan defect
as an independent entity.
Vision; Color.
INDEXHEADINGS:
Many workers with a major interest in color blindness,
including ourselves, have never seen a patient with
congenital tritanopia. Included in this groupl are Alpern,
Linksz, Frangois, Blackwell, and Rubin, who have all
written on the subject of color blindness. Trendelenburg,2 who described methods for discovering and testing tritanopes, could not find a single typical case, nor
could Pitt, 3 who discussed the properties of tritanopia.
This is surprising if the incidence is really somewhere
between
1/10 000 and 1/65 000 as Wright,
4
Kalmus,
5
6
and Schmidt claim. Furthermore, since according to
Wright, 4 tritanopes
know they are color defective,
7
it
would be anticipated that at least some of the workers
cited above would have seen a tritanope since they have
screened populations for color blindness and have
searched for color defectives by advertising.
A possible explanation may be that there is a subtle
retinal or optic-nerve disease with the color-vision
defect described for congenital tritanopia, which may
visual-field defects. Finally, the condition is usually
stationary or only mildly and slowly progressive. The
incidence of this disease is close to 1/50 000, which is
in the range reported for congenital tritanopia. The inheritance of both conditions is autosomal dominant
with frequent intrafamilial and as well as interfamilial
variation in manifestation.
No other optic-nerve abnormality and only a few
retinal abnormalities have dominant inheritance.13-15
Those retinal diseases with this type of inheritance,
such as vitelliruptive
macular degeneration,'
or some
cases of retinitis pigmentosa, almost always have
obvious visual complaints, if they have a significant
color defect, and show obvious progression with time.
In hereditary dominant optic atrophy, not only may
affected individuals believe that their eyes are normal,
but an examiner may miss the diagnosis, particularly in
mild cases, which are frequent. This is likely to be so if
the examiner relies on the history of the patient and
tests only near vision. Distance acuity may be as good
as 20/30 or better and therefore not considered to be
We intend to explore this possibility in this paper.
It is our feeling that the only disease that has all the abnormal. In a few patients, distance acuity may be
8 9
characteristics described for congenital tritanopia is normal. ' Visual fields, tested in the usual clinical
hereditary dominant optic atrophy. This condition is manner, frequently show only mild abnormalities, or at
characterized by a pallor of the optic nerve. The visual times, appear normal. Even the optic nerve may show
acuity and visual fields may be normal or close to only questionable pallor or appear normal in some
normal so that the affected individual claims to have individuals. Therefore, it is of vital importance to
examine the optic disks of more than one member of an
good vision with no eye disease. In his color vision, the
patient shows a blue-yellow defect and either he or his affected family (even those who claim to be normal)
relatives usually notice this color problem. The patient because some members usually show obvious opticwith hereditary dominant optic atrophy may not be nerve pathology.
In the past, it has been emphasized that patients
aware of a visual problem, other than a color defect,
for several reasons.-- 3 First, the disease usually begins with dominant optic-nerve atrophy often show blueearly in life, possibly even at birth. Often there is very color-vision abnormalities, but usually testing of color
little impairment of acuity, particularly for reading. vision was limited to use of the pseudoisochromatic
These patients do not complain of nightblindness or plates. We have had the opportunity to determine
have been called congenital tritanopia by some workers.
1132
August
1970
TRITAN
DEFECTS AND DOMINANT OPTIC ATROPHY
1 133
TABLE I. Visual-screening results.
Age
Distance
vision
Near
vision
IIb
hIg
IIi
32
39
34
20/25
20/60
20/30
J1
J1
J1
IIIk
14
20/60
J2
III1
Illm
IIIn
9
11
13
20/200
20/200
20/80
44
15
24
17
38
12
11
Case
Visual
fields
Optic
nerve
Defect
unknown
Family 1
...
...
...
*-.
T.P.C
N
T.P.
Yes,
Yes,
Yes,
T.P.?
Yese
J4
J5
J2
*..
*..
...
T.P.
T.P.
N
Yesf
20/30
20/30
20/200
20/100
J1
J1
J7
J6
Na
...
C.S.b
C.S.
T.P.
T.P. RE?d
T.P.
T.P. RE
Yese
Yese
20/30, 20/25
20/40
20/60
JP
J1
J1
T.P.
T.P. RE?
P.
Yeso
Yesf
Yes,
Family 2
lb
Ilc
Ild
Ile
Yesf
Family 3
lIb
IIIa
IIIb
a
b
e
Normal.
d
Central scotoma.
Temporal pallor.
e
N
N
N
Right eye.
Visualabnormality detected at eye clinic.
f Visualabnormality detected by schoolscreening.
neutral points and confusion colors, in addition to some
Family 3 was also referred for electroretinography
of the usual clinical tests, in several families with this
condition. The purpose of this report is to show that
the color vision abnormality in some individuals with
hereditary dominant optic atrophy is identical to that
reported for congenital tritanopia.
because the cause of abnormal acuity in subject IIIa
was uncertain. She was thought to be normal until she
failed a screening examination in school. On initial
evaluation, we were uncertain of the diagnosis; however, optic-nerve pallor was obvious in both this girl's
sister (IIIb) and her father (.IIb).
Most of the subjects who were unaware of abnormal
visual acuity and an optic-nerve disease nevertheless
SUBJECTS
Figure 1 shows pedigrees for three families with
dominant optic-nerve atrophy. The visual data are
summarized in Table I.
Family 1 was first seen because three children (IIIi,
HIm, and IIIn) failed visual-screening examinations in
school and the referring ophthalmologist wanted confirmation of his impression of optic atrophy in at least
two of these three individuals. By history, two of the
three individuals (IIIi and IIIm) were known to have
had abnormal vision since early childhood. One (IlIn)
was thought to be normal until he failed a screening
examination in school. Six other members of this family
were examined at our clinic and four were considered to
have the disease (Fig. 1 and Table I).
One member of family 2 (IId) was initially seen in
1958 because of unexplained low acuity. This boy was
thought to be normal until he failed a visual test in
school. A diagnosis of optic-nerve atrophy in this
patient was not made and he was referred for an
electroretinogram (ERG) in the hope that some insight
would be gained into the cause of the visual loss. It was
learned that his sister (IIc) was known to have had
abnormal vision since early childhood. The diagnosis of
hereditary optic atrophy was uncertain in subject IId
until subject IIc was examined. Furthermore, the
father was found to have the same condition, although
he claimed to be normal.
were aware of some color-vision
difficulty,
or their
relatives pointed this out.
METHOD
Distant visual acuity was tested with Snellen letters
projected 6 m from the subject with an American
Fcmily No. 1
I
a
b
e-f
b
a
c
d
e
g
h
,
j
k
Family No 2
I
m
Family No 3
7
a
b
b
c
&>
I
U
a
d
3?
5?
a becd
n
e
f
a
b
?
01
b
c
d
L
a
b
c
e
d?
d
e
?
FIG. 1. Pedigrees for three families with hereditary dominant
optic atrophy: *, N, female or male with tritanopia; @, 62,
female or male with tritanomaly; 0i, poor vision known; ',
color-vision data not reliable; l, G, female or male with optic
atrophy, no color-vision testing; \/, examined; ?, status uncertain; = cousin marriage; o sex unknown.
KRILL,
SMITH, AND POKORNY
Optical projection lantern. Near vision was evaluated
with a Lebensohn chart. The test distance varied from
23 to 33 cm dependent
on the size of the individual.'
7
Both distant and near vision were tested with the bestpossible refractive correction.
Visual fields were done in six subjects
(Table I) with
the Goldmann perimeter. This intrument employs a
projection device and a self-recording method with a
controlled spot of light as a target. The contrast
between target and background illumination can be
varied by a series of neutral-density filters. The projected target size can be varied from 1/16 to 64 mm
and
red, green,
and blue filters can be interposed.
Fixation of the subject is observed through a peephole
in the instrument. In the six subjects tested, only the
white light was used and the smallest target size used
was 1/4 mm (1.8').
Dark adaptation was evaluated in subjects IlIm of
family 1 and IId of family 2. An ERG was obtained from
subjects II~m of family 1, IId of family 2, and IIIb of
family 3. The methods used for dark adaptation and
the ERG are described elsewhere.' 8 -20
The color-vision tests used included the FarnsworthMunsell 100-hue test, the Nagel anomaloscope, the
American Optical Hardy-Rand-Rittler
pseudoisochromatic plates and the determination of neutral
points and confusion colors.
The Farnsworth-Munsell 100-hue test was given and
evaluated in the usual manner described in the directions that accompany this test. It was administered
monocularly under a Macbeth easel lamp that provided
a white light with color temperature of 6740 K. In
scoring the 100-hue test, we considered both the total
errors and the regions of greatest concentration. In
general, the number of errors on this test increases with
Vol. 60
field, as well as the yellow luminance, was noted. At
least five red-green ratios, covering the full range of the
instrument, were evaluated. Between each pair of
matches the subject was light adapted for 10 s. Our
normal subjects were volunteers or patients with normal
acuity and color vision. The average midpoint for an
equation was a red-green ratio setting of 50 with a
range of 44 to 54 on the Nagel scale varying from 0
(green) to 73 (red). Any median setting outside this
range was considered to be abnormal, as was a match
width greater than 5 units on the Nagel scale.
For the determination of color confusions and the
neutral point, the patient observed a 30 bipartite field
presented within a 10° surround.2 The 3° bipartite
field was illuminated by the outputs of two Bausch &
Lomb grating monochromators. The 100 surround was
illuminated by a tungsten lamp with a color temperature
of 2500 K and maintained at a constant retinal illuminance of 16 td.
For the determination
experimenter
of color confusions, the
set different wavelengths
on each side of
the bipartite field. One side was set at a standard retinal
illuminance of 16 td and the other side was varied in
luminance. The patient was asked to name the colors
of the lights on each side, to state whether both sides
of the field had the same brightness, and to indicate
whether both sides of the field had the same color.
Initially, 420 nm at 16 td was set on one half of the field
and 530 nm (variable luminance) was set on the other
half of the field. If no manipulation of luminance at
530 nm resulted in a judgment of "same color," the
wavelength of the 530-nm field was changed to 520 nm
age,2 ' but our oldest subject was only 44 (Table I). A
total error score greater than 110 was considered to be
and the procedure was repeated. Various pairs of wavelengths between 420 and 530 nm were presented in a
similar way until the experimenter determined whether
a color match could be established.
For the determination of the neutral point, the 3°
abnormal, for the subjects studied. The axis for a
field was filled entirely by the output of a single mono-
specific region of errors was a line drawn through the
center of this area. According to Farnsworth, 2 2 a tritan
axis is centered near the vertical meridian, a protan
chromator, and the patient compared the color of the
30 field with that of the 100 surround. The experimenter
set a wavelength and the patient was asked to name
axis near the horizontal meridian, and a deutan axis in
the color of the central field, to state if the central field
the oblique meridian bisecting the area between caps
and surround were of equal brightness, and to indicate
if the central field and surround were of the same color.
A number of wavelengths were presented in turn in the
central field to establish the reliability of color naming
by the patient.
56 and 61.
Anomaloscopic evaluation consisted of fixed matches
by all patients. In a fixed match, the examiner sets the
dial controlling the mixture of red and green and the
subject attempts to make brightness, and when possible,
color matches by moving the dial controlling the luminance of the yellow half of the bipartite circular field.
Five minutes of light adaptation preceded testing.
The range of red-green ratios was determined for
which the subject matched the two halves of the circular
field in color and brightness. The midpoint, as well as
the width (range) of the color and brightness-match
area, was noted. Where only brightness matches could
be made, the subject's color name for both halves of the
RESULTS
A. Visual Acuity
Of the 14 individuals thought to be affected, nine
had distance acuity equal to or better than 20/60. None
of the nine subjects had 20/20 acuity, but all except
one (family 1, IIIk) were able to read the normal line
(JI) on the Lebensohn chart at the near test distance.
Even this individual was able to read down to J2, a
August1970 TRITAN
DEFECTS AND DOMINANT OPTIC ATROPHY
TABLE
F-M 100-hue test
Case
Age
Errors
Axis
1135
II. Color-vision findings.
AO-HRR plates
screen diagnostic
BY
BY
RG
Nagel equation
RE: 580-585 nm
LE: 581 nm
580-585 nm
None
...
...
RE: None
Neutral point
Color match
Family 1
Ilb
32
...
IIg
39
Iii
IlIk
34
14
RE: 447
LE: 318
220
RE: 591
HE11
HIm
IIIn
9
11
13
Unreliable
Unreliable
RE: 245
...
LE: 644
...
Ta
1
0
0
T
T
2
2
1
4
1
4
RE: 50-54
LE: 48-53
43-52
RE: 46-S51
0
Unreliable
Unreliable
RE: 49-54
T
LE: 342
Unreliable
Unreliable
1
0
LE: 49-53
LE: 51-53
...
...
4103520
420=510
4209510
420a510
nm
nm
nm
nm
...
...
No match
LE: 581-585
4503480 nm
Family 2
Ib
IIc
44
15
IId
24
Ile
17
248
60
RE:
LE:
RE:
LE:
484
655
529
406
T
1
1
0
0
0
0
*
RE: 49-52
579-585 nm
LE: 51-52
440-510
...
nm
...
T+Db
2
2
3
RE: 45-62
LE: 32-62
T+D
1
0
2
52-53
None
No match
1
0
0
RE: 48-50
None
No match
RE: 582-584 nm
LE: 575-587 nm
420=530 nm
420=520 nm
Family 3
IIb
38
120
T
lIla
IlIb
12
11
150
190
T+D?
T
a Tritan axis.
b
LE: 50-52
0
1
0
0
0
0
51-52
51-52
None
579-582 nm
No match
0-530 nm
42
Deutan axis.
line above normal. All nine were initially unaware of a
visual problem. One was detected
on school screening
and eight others were detected in our clinic. Two of the
other four subjects whose acuities were worse than
20/60 were unaware of a visual problem until they were
detected in school screening.
B. Visual Fields
Four of the six visual fields obtained were normal.
The other two showed central scotomas (Table I).
C. Optic Nerves
Obvious pallor of some portion or all of the temporal
portion of the optic nerve was seen in one or both eyes
of eight individuals (Table I). A ninth subject had
pallor of the entire nerve head. Three individuals had
questionable pallor (not all examiners agreed). Normalappearing disks, according to all examiners, were seen
in two individuals.
D. ERG and Dark Adaptation
These tests were normal in the subjects studied.
E. Color Vision
Table II shows the results of the color-vision tests
performed on all patients. Two subjects (family 1,
III1 and IIIm) were unreliable.
Figures 2-4 show the results of the 100-hue test for
three members of family 1 (Fig. 2), two members of
family 2 (Fig. 3), and three members of family 3 (Fig.
4). A tritan axis was seen for all individuals for whom
testing was performed and considered reliable. In
addition, two subjects (family 2, IIc and IId) and
possibly a third (family 3, patient IIIa) showed a
deutan axis, in addition to the tritan axis. All subjects
except one (family 3, patient IIIa) with 20/60 vision
or better showed predominately
a tritan axis.
Subjects considered to be reliable on the anomaloscope gave normal Rayleigh equations, with two exceptions (family 1, IIi and family 2, IId). They had
wider than normal match widths (Table II).
Neutral points were found in six subjects (Table II).
In general, these varied from 579 to 585 nm although
one subject (family 2, IId) showed a neutral point for
her left eye, extending from 575 to 587 nm (this subject
is classified as a tritanope
because of the finding of a
neutral point and characteristic color match. Obviously
her defect extends extensively into the red-green area
as well). Confusion color matches varied slightly, but
when these were plotted along with the neutral points
on a chromaticity diagram, they converged towards the
blue end of the spectrum, in the area of the classical
tritanopic
convergence locus (Fig. 5).
In summary, the four subjects who have the colorvision characteristics classically described for congenital tritanopes are subjects IIg and IIi from family 1,
subject Ib from family 2, and subject IIIb from family
KRILL,
Patient i g
SMITH, AND POKORNY
Vol. 60
Some of our optic-atrophy subjects missed some redgreen pseudoisochromatic plates. In addition, two
Putient
fi
subjecLs with poor vision showed a deutan as well as a
tritan axis on the F-M 100-huetest. In pedigrees with a
tritanope there are frequently some affected individuals
showing evidence of slight red-green abnormalities on
the pseudoisochromatic plates and 100-hue test.' 2 a
On the anomaloscope, all but two subjects showed
normal Rayleigh matches. These two had wider than
normal equations. A slight red and rarely a slight green
Patientm k
FIG. 2. Plot of errors on Farnsworth-Munsell
100-hue test
from three patients in family 1. A tritan axis is noted in all three
patients.
3. All these subjects had normal reading vision and
were unaware of any visual defect other than abnormal
color vision. All had classical tritanopic neutral points
and color matches and showed only tritan axes on the
Farnsworth-Munsell 100-hue test.
DISCUSSION
A. Comparison with Other Tritan Data
The color-vision data of members from these three
families and from pedigrees with congenital tritanopia
are identical. Almost all affected individuals of both
groups showed a tritan axis on the FarnsworthMunsell 100-hue test. Of the 14 affected subjects,
all
except one missed at least one screening blue-yellow
plate on the AO HRR pseudoisochromatic plates. This
plate is rarely missed by other types of observers.
Walls24 reported
that each of his five tritan
subjects
missed some of these blue-yellow plates. On the other
hand, only three of the eight tritans tested by Henry,
Cole, and Nathan2 5 missed some of these plates, but the
other five tritans reported two or more of the plates to
be faint.
FIG.
3. Plot of errors on Farnsworth-Munsell 100-hue test
from two patients in family 2. Tritan axis is noted in both patients
and in addition, a deutan axis is evident in patient Ild.
August1970 TRITAN
DEFECTS AND DOMINANT OPTIC ATROPHY
Patient flb
~
-'
I'
\
Our pedigrees were characterized
\ \I/
Patient
ma
\
Itritanopia
dominance,
and the variability
;mon
/ \
' ><
m<5 m\
4/tAfound
XIn
mb
B. Comparison with Color-Vision Data
from Other Acquired Diseases
other acquired diseases we and Verriest31 have
a tritan axis on the 100-hue test to be very common in macular disease. However, in our experience
and that of Verriest3' and Hong32these patients almost
always show a red shift of the Rayleigh equation and,
in addition, frequently a widening of the equation,
exceeding the normal range. In addition, we have found
that patients with minimal or early macular disease
may show only anomaloscopic abnormalities without
changes in the 100-hue test. In dominant optic atrophy,
a tritan
axis on the 100-hue test is frequently
of acquired optic-nerve
disease, a deutan
axis is com-
mon on the 100-hue test, and a green shift of the
30 32
Rayleight match on the anomaloscope.
Therefore,
the color vision of patients with hereditary dominant
optic atrophy is different from patients with macular
and other optic-nerve diseases.
FAMILY No.1, PATIENT
100-hue test
from three patients in family 3. A tritan axis is evident in patients
I1b and IIIb; however, patient
ans.
axis.
seen
an anomaloscopic abnormality. In other types
|without
*
FIG. 4. Plot of errors on Farnsworth-Munsell
of expression are com-
features.
/
e
by variations of the
degree of color-vision abnormality in affected members.
Similarly, variation is common525 in pedigrees with
and even unilateral tritanopes are described.4' Obviously, the hereditary pattern, autosomal
/
4
Patient
1 137
Ilg
FAMILY No.2, PATIENT
lb
as
0.8
0.
0.7
ila shows a mixed deutan-tritan
\I
0
Oe\\06\\
shift have been reported,5 25' 26 but apprently most
tritanopes have normal equations of the anomaloscope.
The neutral points reported for our optic-atrophy
patients varied from 579 to 585 nm with 2500 K and
were in the range reported for tritanopes by Wright4 ;
Judd, Plaza, and Farnsworth2 7 ; Cole, Henry, and
Nathan2 5 ; Fischer, Bouman, and Ten Doesschate.;2
and Sperling. Only one other study30 evaluated neutral
points in dominant optic atrophy. However, both of
the patients studied had very poor acuity and matched
most of the spectrum to white light.
04
04
03
0.2
0/
/
01
,
0'2
a
0'4
of our subjects were plotted on the chromaticity
dia-
gram, convergence to the blue end of the spectrum
in the area of the tritanopic-convergence
found.
locus was
s
a0'
O.
0'7
0.'
0.6
07
0
x
FAMILY No.1, PATIENTIUi
FAMILY
No.3 PATIENTII,
0.8
0.
O,
07
The color confusions reported for our subjects corre-
sponded to those noted in tritanopes. For example,
Wright4 most commonly found that tritanopes confused 530 and 420 nm. Our optic atrophy subjects
matched 410 nm with 520 nm, 420 nm with 510 nm, \
and other similar combinations. However, the major
point is that when the neutral points and color matches
/
06
\
\O
05
f
I
.4
04
05 \F
0X/
/0
0'
02
03
04
0506
07
0.8
\/
0 0'
.3
04 05 06
0
0
FIG. 5. Plot of neutral points and confusion colors from four
patients with tritanopia on a chromaticity diagram. Note convergenre
of
fnertnnyP
- --__ nointqin
___the
___airen
____ of
__ the
___blue
-_ end
__ of
-1 the
- _V_- -
1 138
KRILL, SMITH, AND POKORNY
C. Characteristics of Hereditary
Dominant Optic Atrophy
The subtle nature of the visual defect in hereditary
dominant optic atrophy, referred to by many
workers8 -1 2 in the past, was emphasized by the data of
this study. Six patients were unaware of a visual
problem until this was detected at our eye clinic. Five
of the six patients were beyond the age of 30 and would
therefore be similar to the age range of many of the
tritanopes previously reported. It has only been in the
last 5 to 10 years that routine visual screening has
become a practice in many school systems. Five of our
younger patients were discovered to have a visual defect
in this manner. None of these five were previously
aware of any visual difficulty. Altogether, then, only
three of the 14 patients reported in this study were
aware of a visual defect since birth, or early childhood.
However, most of our patients or their relatives were
aware of abnormal color vision (a finding noted by
Wright 4 in his study of congenital tritanopia).
The original examiners of our patients frequently
did not detect the disease if only one member of a
family was examined, because of the subtle nature of
the optic atrophy. Temporal pallor, the most frequent
optic-nerve change, was borderline in some patients.
Two patients were originally referred to us because the
ophthalmologist was unaware or uncertain of the cause
of abnormal distance acuity. In both cases other members of the family who exhibited obvious optic atrophy
had not been examined.
Obviously, the degree of temporal pallor varies, even
within the same family. When of sufficient extent, it is
easily recognized and is unlikely to be confused with
other anomalies or diseases of the optic nerve by the
experienced examiner. The significance of the temporal
pallor in these patients is uncertain, but may reflect
an absence of some nerve fibers, and accompanying
blood vessels, perhaps in most cases, since birth.
It should be emphasized that most patients had
acuity sufficient to read fine print (J2 or better) without
bringing the subject material closer than the test
distance customarily used for a normal individual about
the same size. This was true of all subjects with distance
acuity equal to or better than 20/60. This discrepancy
between near and distant vision (assuming the visual
angle to be about the same) has been commented on
previously by one of the authors3 3 as a frequent finding
in certain congenital conditions, such as albinism or
rod monochromatism. We have not seen this discrepancy in diseases affecting vision, acquired later in
life. Therefore, the frequent finding of this discrepancy
in dominant atrophy supports the notion that this
disease is usually present since early life, perhaps since
birth.
Previous reports8'- 3 on dominant optic atrophy
emphasize the variability as well as the frequently
subtle nature of the disease. Some of the major points
Vol. 60
that have been emphasized in these reports are: (a) The
optic atrophy varies in extent, but in the majority of
patients only the temporal half of the disk is pale;
(b) in most cases, it was not difficult to establish the
presence of atrophy of the disk, but in some patients
the pallor was so slight that the first impression the
disk gave was that it was normal. Kjer,8 in his very
extensive study of this disease, cites four patients for
whom the original examining ophthalomologist had
not considered the disk pallor to be pathological. He
also emphasized that atrophy was sometimes more
apparent by indirect illumination; (c) in doubtful cases,
supplementary examinations (determinations of vision,
color perception, and visual fields) helped to decide
whether a pale disk should be regarded as pathological
or merely a physiological variation; and (d) in many
patients, there was no direct relationship between
optic-disk atrophy and visual acuity. In fact, Kjer8
describes pale disks in some patients with, normal
vision, while in other patients optic atrophy was difficult
to recognize, whereas vision was obviously impaired.
Only two of the six patients we examined showed
visual-field defects. However, as pointed out in the
Methods section, we did not use the most-sensitive
test target of the Goldmann perimeter, nor did we use
colored test objects. It has been noted in previous
studies8-13 that the majority of patients have minimal
visual-field defects that can be detected with small
enough white or blue test objects. It is of interest that
in two patients with congenital tritan defects,34' 35
visual-field defects were more pronounced with blue
than any other-color test object.
CONCLUSIONS
It is conceivable that congenital tritanopia actually
exists and that all of the similar or identical findings
mentioned in this report are coincidental. We propose,
however, that certain criteria should be met before a
case called congenital tritanopia can be accepted as a
unique entity, differing from dominant optic atrophy.
First, it is necessary to show that both distance and
near vision are normal. For example, it is not enough
to say that visual acuity was sufficient to read small
print, 5 adequate to carry on a certain profession,27 or
sufficient to permit reliable results to be obtained from
color tests. 25 Second, visual fields must
be normal.
Third, not only the affected individual, but other
members of the family should have normal-appearing
optic nerves as well as normal acuity. Further, the
ophthalmoscopic examination should be done by some
one who has evaluated many pathological optic nerves,
because the changes can be quite subtle, as we have
noted. Evaluation of previous reports of tritanopes,
particularly within the last 50 years, reveals that all
these criteria have usually not been fulfilled.
This report does not prove that congenital tritanopia
does not exist; it serves only to emphasize that there
August1970
TRITAN
DEFECTS AND DOMINANT OPTIC ATROPHY
is a condition, dominant optic atrophy, that presents
all the characteristics reported for congenital tritanopia.
Therefore, we emphasize that for future subjects in
whom congenital tritanopia is suspected, the utmost
care should be taken to rule out dominant optic atrophy.
REFERENCES
* This study was supported in part by Grants EY-0523-09 and
EY-00277-05 from the National Institutes of Health, Public
Health Service, and also by a grant from the National Society for
the Prevention of Blindness. Paper presented at the Chicago
meeting of the Optical Society of America, October, 1969 [J. Opt.
Soc. Am. 59, 1533A (1969)].
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