CASES ILLUSTRATIVE OF DIFFERENT FORMS 
OF COLOR-BLINDNESS. 
CASE I.—CONGENITAL COLOK-BLINDNESS. 
CASE II.—TOBACCO COLOK-BLINDNESS. 
CASE 111.—TRAUMATIC COLOR-BLINDNESS. 
A Clinical lecture delivered before the Senior Class at the Jefferson 
Medical College, Philadelphia, April 5, 1595. 
BY WILLIAM THOMSON, M.D. 
PROFESSOR OF OPHTHALMOLOGY IN THE JEFFERSON MEDICAL COLLEGE; 
OPHTHALMIC SURGEON TO THE PENNSYLVANIA RAILROAD, BTC. 
REPRINTED fßObyltSl 
JOURNAL OF THE AMBRJfLAM JLEDICAL A^QQIAIJON'r 
FEBKIIAKI S7 1896. 
American Medical Association Press. 
1890. 
CHICAGO: CASES ILLUSTRATIVE OF DIFFERENT FORMS 
OF COLOR-BLINDNESS, 
CASE I.—CONGENITAL COLOR-BLINDNESS. 
CASE II.—TOBACCO COLOR-BLINDNESS. 
CASE 111.—TRAUMATIC COLOR-BLINDNESS. 
A Clinical lecture delivered before the Senior Class at the Jefferson 
Medical College, lBl5. 
BY WILLIAM THOMSON, M.D. 
PROFESSOR OF OPHTHALMOLOGY IN THE JEFFERSON MEDICAL COLLEGE; 
OPHTHALMIC SURGEON TO THE PENNSYLVANIA RAILROAD, ETC. 
REPRINTED FROM THE 
JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION, 
FEBRUARY 8, 1896. 
CHICAGO: 
American Medical Association Press. 
1896. CASES ILLUSTRATIVE OF DIFFERENT 
FORMS OF COLOR-BLINDNESS. 
Gentlemen:—Your Clinical Professor of Ophthal- 
mology has invited me to address you on the subject 
of color-blindness. I must suppose that you have 
been made acquainted with the anatomy and physi- 
ology of the eye, by the teaching of my friend and 
colleague, Professor Hansell, who is so well qualified 
to instruct you upon this subject. Taking, therefore, 
your familiarity with these preliminary matters for 
granted, I will proceed at once to tell you what is 
meant by colorblindness; and how the condition 
may be recognized. I will also explain the tests, and 
give you clinical illustration of their application. In 
this way, you will get a practical demonstration of 
the methods of examining patients who are suspected 
of having a defective color sense. 
When we speak of congenital color-blindness, we 
mean that the eye may be perfectly normal in its 
structure, have no anomaly of refraction, and be a 
perfect optical instrument, except for one defect, and 
that is the inability to distinguish the difference 
between colors, which to ordinary, normal eyes is 
very obvious, such as red and green. It is precisely 
these colors, however, which have been selected for 
signals on the railroads and on shipboard, where 
failure to recognize them may cause serious loss of 
life and property. You will appreciate this better 
when I tell you that there are cases of total color- 
blindness in which the solar spectrum looks to the 
patient like a lead-pencil drawing of it; where, from 
red to indigo, the spectrum looks as if drawn in dif- 
ferent shades of gray. Such cases, however, of total 
color-blindness are rare; indeed, I have never met 4 
with a case of this kind. On the other hand, cases 
of partial color blindness are common. For instance, 
there is blue, yellow, red, and green blindness. What 
is most commonly meant, at the present day, by 
color blindness, on occount of its wide-spread and 
far-reaching consequences, is the inability to distin- 
guish between red and green, or green and gray. 
When you realize that the individual presenting this 
defect to the examiner would show the same in ability 
to distinguish between red and green flags or lights, 
which are commonly used as signals at sea or on 
railroads, you will understand the great importance 
of testing the eyes of all pilots, and of engineers and 
brakemen particularly. The correct interpretation 
of those signals depends upon the ability df the 
engineer or lookout to recognize certain colors at 
sight. The white light or flag on the railroad means : 
“Go ahead;” the green, “ Proceed with caution;” 
the blue, “ Do not move it;” but the red light or 
flag means imperatively, “ Halt.” It is important 
to recognize lights at sea, for another reason, because 
by their aid the course is indicated in which a ship 
is sailing. The red light is hung at the port and the 
green at starboard, with a white light on the mast- 
head. By the relative positions of these lights the 
direction may be known. In the recent calamity by 
which the steamship Elbe was injured in a collision 
in the North Sea and foundered with all on board, I 
am not sure that it was not due to the defect in vis- 
ion of which I speak to-day. The accident occurred 
at night when there was no storm, and the atmos- 
phere was clear enough for ships to see each other 
for a long distance before they met. It might have 
been due to the fact that the lookout on the Craithie 
could not tell which way the Elbe was going, owing 
to color-blindness, which prevented him from cor- 
rectly interpreting the signals on the Elbe. . So, you 
see that this is a matter of very great importance, 
especially to all of us who may have occasion to 
travel by land or water. 5 
Now, we will see if we can approach this subject 
in some way so that you will get a clear idea of the 
color sense and of the relations of colors. Here, on 
this plate 1 show you a colored representation of what 
is commonly known as a “spectrum” “or solar spec- 
trum.” This teaches you that if you go into a dark 
room and make a small hole in a shutter, that the 
beam of light (or if passed through a prism) will break 
up into this arrangement of colors upon a screen, 
with blue light at one end and red light at the other, 
as everybody knows. The reason why the spectrum 
is formed is because a beam of white light is made up 
of a number of rays having different wave lengths, or 
rates of vibrations. Thus, the red rays at one end of 
the spectrum have about four hundred million mil- 
lions of vibrations per second, while the violet at the 
other end have over seven hundred and fifty million 
millions. All rays under four hundred billions of 
vibrations per second are not perceptible as light and 
are known as heat rays, while those higher than the 
violet can not be appreciated by the human eye and 
are only recognized by their chemic and physical 
effects. Between these extremes of red and violet are 
found the orange, yellow, green and blue rays with 
rates of vibration of four to eight billions per second. 
You may ask why it is we see only a small portion 
of the spectrum, and that the higher and lower rays 
are not luminous. It is because the human eye has 
been evolved from lower forms of animal life, and its 
condition is the result of the action of external forces 
of nature upon it during the course of its development 
to fulfill the needs of the human organism. We will 
suppose that the light falls upon the cornea and 
passed through the crystalline lens and that impact 
takes place upon the retina. A commotion is set up 
among its rods and cones, the red rays and violet 
rays make a different impression upon the nerve 
endings in the cones, and this is carried backward 
through the optic chiasm to the part of the brain 
which we have ascertained, by pathologic and other 6 
observations, to be the center for vision, which is 
situated in the occipital lobe of the brain in the 
cuneus. From here it is carried on to consciousness, 
and if any of you, gentleman, can tell me where that 
is and how these impressions become conscious sen- 
sations, I shall be very much obliged to you for the 
information. Having traced the impression to the 
cortical center in the occipital lobe, there we must 
leave it for the present; all we know is that it is car- 
ried to the cuneus and thereafter it becomes to us 
conscious sensation. 
Case 1. Congenital Color-Blindness.—Now, gentlemen, 1 
will show you this case of color-blindness, in order to demon- 
strate the nature of this phenomenon to you. I will first give 
him fine print to read and thus test each of his eyes, to prove 
to you that they are perfect as optical instruments, and that 
vision is acute and accommodation normal. He says that he 
first learned that he was color-blind when he bought what he 
thought was a blue necktie, and when he brought it home he 
was laughed at for buying a green one. This led to conver- 
sations upon colors, which showed him there were differences 
recognized by others, but which he could not appreciate. 
It is of interest to mention that it is to Dalton, who was 
himself afflicted in this way, and who a hundred years ago was 
a distinguished professor of chemistry, that we owe our first 
exact views on the subject of color-blindness. He also ascer- 
tained the peculiarity by accident. He was living at Oxford, 
and when he went up to take his degree he was informed that 
he must wear a red coat, and it being against the rule of the 
religious society to which he belonged, he was much troubled 
about it. When the coat was brought home, he thought that 
they had changed it for a mouse-color or drab and he was 
very much pleased with the shade. He thought so well of it 
that he not only wore it to the ceremony when he received his 
degree, but he also wore it in the street until his friends spoke 
to him about it, when he learned for the first time that the coat 
was red. He investigated this subject and taught the use of 
the spectroscope in diagnosis. After Dalton came Dr. Thomas 
Young, who made observations upon the color sense, which 
have become classic. Now, coming down to our own time, 
Holmgren taught us that color-blindness was comparatively 
common among the railway employes in Sweden, and devised a 
very practical test for the examination of their color sense. 
Now, let us suppose that you will be called upon to examine 
a suspected case. It will be useless to ask him to name colors, 
for he has learned to apply these names which he will use in 
speaking, although he could not distinguish the green from the 7 
red, perhaps except by a slight difference of shade, both appear- 
ing as dark gray. Now, according to the doctrine of probabilities, 
if you take a large number of men, you will find that 4 men out 
every 100 will not be able to distinguish between red and green, 
or will be color-blind ; whereas there are only about 4 women 
out of 6,000 who are color-blind. This would really show on 
this point, a superiority of the female sex, in the ratio of 1 in 
25, in males, to 1 in 1,500 females possessing this defect of color- 
blindness. 
We will now proceed to the test for color-blindness. The 
best way to ascertain the existence of this condition is to ask 
the subject of the test to match certain colors. Here is a mass 
of over a hundred small bundles of wool of different shades of 
green, pink, blue, orange, etc. In making then, what is known 
as Holmgren’s test, three test colors, viz., light green, rose or 
purple, and red are placed in turn before the person to be ex- 
amined, and he is told to select from the mass a number of 
skeins and to sort them according to the color. 
This test will now be made upon our patient. Observe that 
he takes a rose-pink and lays upon it the light blues and 
hesitates about the grays. In assorting the colors, as requested, 
you can see, without asking him any questions, that he is un- 
able to distinguish between certain colors, and especially green 
and red, and makes ludicrous mismatches. He reminds me of 
a young man who happened to be color-blind, and who describ- 
ing his ladylove said that her cheeks (pink) were the same color 
as the sky (blue). I have no doubt that there are a number of 
gentlemen in this class who are color-blind, and if so, they should 
know it, in order that they may avoid errors and thus succeed 
in their professional lives. There are many things that appear 
differently to the color-blind physician, and we often depend 
upon full appreciation of color for our diagnoses. For instance, 
a rash upon the skin would not look the same to such an indi- 
vidual as to others with a normal color-sense. Chemic tests, 
dependent upon color changes, would be rendered uncertain and 
difficult to a color-blind doctor. 
Here is a bundle of skeins of wool of neutral colors which 
our patient selects. Here is a pink, which this man calls a 
dirty white. If he were an engineer and should make such a 
mistake confusing a red with a dirty white flag, the results 
might be serious. Now, if we confront this man with the pic- 
ture of the spectrum, we find that he can distinguish blue and 
yellow better than red or green. Therefore, if we divide the 
spectrum into four colors, red, yellow, green and blue, he can 
distinguish yellow and blue well and fails on the other two 
colors, and he has hence that form known as red-green color- 
blindness. 
Some difficulty arises owing to the partial education of the 
color-sense in these cases, so that we can not ask them to name 
the colors, or to select colors by name. But we must ask him 8 
to match skeins of worsted by placing him before this box filled 
with many colors, from which he must select those correspond- 
ing in color to the test skeins, but lighter or darker in shade. 
The rose-pink, as you may know, is a mixture of red and 
blue. Therefore if he matches this with a blue, he is red blind : 
and if he matches it with green or gray, he is green blind. Now, 
you see he gives himself away in two ways ; he not only matches 
the rose-pink with a blue, but fails to pick out the other pinks in 
the mass right before him. He then picks out a bright red and 
throws it upon the green test. This shows that his eye is inca- 
pable of responding to the four hundred million millions of 
vibrations in a second, which correspond with the red color. 
Now, if he were a doctor, and were to examine the eye- 
ground with the ophthalmoscope, the field would look to him 
as if bright green or dark yellow. 
One other point should be mentioned. Nature is very mis- 
erly in her gifts and, while our color-sense is most acute in the 
very center of the posterior segment of the retina, outside of 
this portion of the retina we are all relatively color-blind. The 
response to the color rays becomes less decided as we pass from 
the center to the periphery of the field of vision in normal eyes. 
As our color-blind subject sees in the spectrum only blue and 
yellow, he has a dichromatic color-sense, that is to say, a color- 
sense limited to two color sensations only. The normal sense 
is trichromatic: red, green and violet, which are the three 
color sensations necessary to produce white light. If this man 
should attempt to paint the solar spectrum, he would place 
blue at one end and yellow at the other end, with a neutral gray 
band between, as he has only two color perceptions. His 
entire color scheme of nature most correspond to this fact, and 
would necessarily be very different from that of other persons 
who have all three sensations. Therefore, his appreciation of 
nature is much more limited than that of those with full per- 
ceptions of color. He would not be able to pick strawberries 
out of a patch, or cherries from a tree, except by the form of 
the fruit; and in his eyes a red rose would not be very differ- 
ent in color from its leaves. 
This examination which I have made by Holmgren’s test can 
be very much facilitated and shortened by that instrument 
known as “the color-stick,” which was invented by me in 1879, 
for testing the employes of the Pennsylvania Railroad. The 
simplicity of this instrument and the positive character of the 
results, make it valuable also for preserving records, and it has 
the great advantage that the test can be made with it by lay- 
men and non-professional people. I think that it is always 
better to have a trained surgeon to supervise the examinations ; 
but at the time that this system was introduced it was impos- 
sible to find a sufficient number of ophthalmic surgeons to sup- 
ply the demands of the Pennsylvania Railroad, where there 
were About forty thousand men in the employment of the com- 9 
pany, scattered over thousands of miles of railroad. To accom- 
plish this result, I devised this instrument. It consists of 
forty skeins of worsted, arranged in a single row, upon two 
sticks joined together, but which can be taken apart. Each 
skein has a ring and a little bangle upon which is stamped its 
number. Twenty of these skeins are affirmative and twenty 
are negative; all the affirmative bear odd numbers, all the neg- 
atives are confusion colors and have even numbers. Now, if a 
person’s color-sense is normal, he will select all the odd num- 
bers, while the color-blind person will select a portion of the 
even numbers. As each skein is selected, it is turned back- 
ward so as to hang over the top of the stick. At the end 
of the examination the results are read off and entered upon 
a printed blank form, which is then sent to the superintend- 
ent, who can tell at a glance whether the man is or is not 
deficient in color-sense, by an inspection of his odd or even 
numbers. 
Now we will give this man a skein of green to hold in his 
hand and he is told to pick up some others from the stick 
that look like it. Observe, now, that the even-numbered skeins 
show his mistakes. He is now given a rose-pink and told to 
pick out skeins to match it. The former test is confirmed 
by his selection again of even-numbered skeins. The result 
is read off immediately and recorded on the blank, and color- 
blindness is the diagnosis. 
The new system recently adopted by the Pennsylvania Rail- 
road is the following: The stick has been discarded and the 
test consists of two different sets of worsted skeins which 
must always be kept apart, not only in their corresponding 
parts of this box, but also in testing the men. The first set 
consists of twenty skeins, numbered 1 to 20 on bangles, these 
numbers being so concealed that the men can not see them. 
Among these numbers the odd ones (1, 3, 5, etc.) are greens, 
while the even numbers (2, 4, 6, etc.) are grays or light browns. 
The second set consists also of twenty skeins, but they are 
numbered from 21 to 40. Here the odd numbers (21, 23, 25, 
etc.) are all different shades of rose color, while the ten even 
numbers (22, 24, 26, etc.) consists of four blues, three greens 
and three grays. 
The following directions are to be observed in the use of 
this test: 
1. Examine only one eye at a time, by covering the other eye 
with a handkerchief or some other means, that will exclude it 
from vision. 
2. Spread a white cloth, like a towel, on a table in a good light. 
3. Take out all the worsteds from the green part of the box 
and put them on the cloth at random. 
4. Take from this heap the _ large light green test skein 
which is marked A, and laying it to the side in a good light 
direct your man to select ten skeins from the heap. Tell him 10 
that they are not to be exactly like it in every respect, but that 
they are to be of the same color, only a little lighter or darker 
in shade. 
5. Write down on your blank the numbers of the ten skeins 
selected by your man to match the test skein A. If only odd 
numbers appear which he selected promptly, then he is not 
color-blind ; but if even numbers have been chosen, he must 
be more or less color-blind. 
6. Ask him the name of the color he has been matching, or 
any other worsted, and register his answer on the blank. 
7. Remove now all the worsteds and put them back in the 
green part of the box. 
8. Now take out the second test and expose it on the table in 
the same way as before. 
9. Show him the large rose-colored test skein, marked B, and 
ask him to match this with ten worsted in the same sense as 
before the first test. 
10. Register his ten selections on the blank. Now any even 
numbers selected betray and determine definitely his color- 
blindness. If your man selects blues, with the test skein B, he 
is red-blind; if he selects grays or greens, he is green-blind. 
11. Ask him the name of the test skein, or any other skein, 
and register it. 
12. Put down whether his selection was prompt or hesitating. 
13. Finally, as a control upon the test and as a substitute 
for the second and third color-test of the old system, there 
have been arranged especially for the surgical expert, two more 
large test skeins, one c, yellow, and the other d, blue. The 
test c is exposed and you ask your man to match it, if possible, 
by the skeins from Ito 20. If normal in color-sense, he will 
decline or at the most only take the yellow-green skein, but if 
color-blind he will select a number of the green skeins, which 
should be recorded. Then use test d, the blue skein, and let 
him match it from skeins 21 to 40. If normal or green blind 
he will select blues only, but if red blind he will pick out a 
series of roses, which should be recorded. 
The old system is now in actual use by more than forty of 
the principal railway corporations in this country and Europe, 
and over fifty-two thousand miles of railroad are now protected 
by it. It is used not only for those actually in service of the 
railroads, but also for all applicants who seek such employment. 
To make the examination of vision complete, records are also 
kept of the results after testing by Snellen’s test types for 
sight and power of accommodation. 
In Holmgren’s test.as originally conducted, the examination 
took considerable time and required an accurate knowledge of 
the subject on the part of the examiner. By this system of 
mine, the tests are quickly made and recorded, and the results 
are equally positive. 
Now, gentlemen, I think that you are satisfied that I have 11 
exhibited to you a typical case of marked congenital color- 
blindness. This was probably inherited either from his father 
or grandfather, possibly from his maternal grandfather, since, 
as already mentioned, the females usually escape color-blind- 
ness. I think, moreover, that you would not like to ride in a 
train behind a locomotive in charge of this man as engineer, 
who would then be called upon to recognize all kinds of signals 
at a glance by night as well as by day, when as he has just told 
you he sees green as dirty white, and red is indistinguishable 
from green. 
There is another easy test known as the cobalt blue test, 
which I will demonstrate to you. A lighted candle is held 
about ten feet from the patient and a piece of cobalt blue glass 
is held before each eye in succession, the other being closed. 
Now to the normal eye, the flame of the candle should be pink 
or rose surrounded by a blue halo, but this man tells us that 
he sees only one color which he calls blue, and thus demon- 
strates his inability to see any red color, since this glass trans- 
mits both red and blue rays. 
Case 2.—Acquired Color-Blindness of Toxic Origin. I will 
now refer to this other case in which the color-blindness 
instead of being inherited has been acquired. This man for 
twenty years has used tobacco to excess, and he has, as the 
result, a central scotoma, or partial loss of vision with color- 
blindness over a limited area of the retina, involving the yellow 
spot, which is the center of most acute vision. In this large 
colored plate of the eye-ground, I now show you a very fine 
delineation of what we see at the back part of the healthy eye 
by the aid of the ophthalmoscope. Here is the optic disc or 
the entrance of the optic nerve, and here is the yellow spot, 
about 8 degrees to the outer side of the disc. Immediately at 
this point is the fovea, the seat of most acute vision and like- 
wise of the highest development of the color-sense. When a man 
has any lesion in this region, it reduces his appreciation of both 
color and form very materially, if not totally. Outside of this 
central region everybody is relatively color-blind, the periphery 
of the retina being less responsive to color vibration than the 
center. 
To prove to you the color defect, I take this red glass from 
the test case and place it in front of a lighted candle at six feet 
away ; now by replacing it with green we find him unable to 
distinguish between green and red. I now measure the diam- 
eter of the test glass and find it 33 mm. I now bring the candle 
to 33 cm. (or thirteen inches) from his eye and he begins to feel 
the red color of the glass, and distinguishes it quite promptly if 
the lighted candle is moved a little from its position. When it is 
removed farther from the eye he is color-blind, but when it is 
approached, say to 25 cm. (or ten inches) he at once perceives 
either red or green colors, properly. Now, at 33 cm. this stick 
in my hand, of 33 cm. in length, covers 60 degrees of his retinal 12 
surface; the red or green glass is 33 mm. or one-tenth the size, 
and hence covers 6 degrees of his retina, and as he is color-blind 
for an object of this size, we are able to prove that within 6 
degrees at his fovea he is color-blind, but if a larger portion of 
the retina is covered by the image of the test, it responds in a 
normal manner. From this, you will infer that this man would 
be incapable of seeing the signal-lights at night and would mis- 
take red for green, or white for green, but that he would escape 
detection perhaps if tested by any colored wools, since each skein 
would form an image of more than 6 degrees upon his retinal 
center, and would touch rods and cones with normal sensation. 
Such cases are rare, and should be remembered by those who 
have the charge of lookouts on the water, or on railways on land. 
Accidents, alcohol, some of the fevers, may cause this condi- 
tion and would render reexamination of suspected men necessary 
even after they had once passed the color-blind examination.1 
This, then, is a case of acquired color-blindness wieh central 
scotoma only, due to excessive use of tobacco; and it differs 
from the preceding case in being amenable to treatment by 
tonics, such as strychnin, etc. 
CaseS.—Traumatic Color-Blindness. I have another case 
to show you but the termination of the hour will permit me 
only to advert to it very briefly. This patient sustained a severe 
injury some months ago. He fell down twenty or thirty feet 
into an elevator shaft and suffered a concussion of the brain. 
At this time he probably sustained a lesion of the cuneus in 
the cortex of the occipital lobe of the right hemisphere. It 
was ascertained recently that he has hemianopsia for color 
only. One-half his field of vision in each eye, is color-blind, 
while he has a perfect appreciation of color and form in the 
other half. 
I show him to you as a case of traumatic color-blindness lim- 
ited to one-half of each eye, following an injury to the occipital 
region. lam indebted to Dr. A. G. Thomson for this case. 
With this case, I conclude the clinical remarks I 
wished to make upon these three patients, which will 
illustrate the congenital, the acquired and the trau- 
mated forms of this very interesting and very im- 
portant condition of so-called color-blindness. 
i This man recovered his full sight both for form and color under 
disuse of tobacco, and Internal use of strychnia. His color scotoma 
extended for 6° and involved the central or macular band of nerve 
fibers only.