CHAPTER XII.
I will now give in full the result of the examination of a patient who was suffering from tobacco blindness. X., aged thirty-six, a commercial traveller, was suffering from rather severe tobacco amblyopia. The scotoma was a very marked one, and the loss of colour sensation most complete. Mr. Nettleship, who furnished the case, has kindly added the following remarks on the case:—
His acuteness of vision was 6/36 with the right eye and 6/60 with the left. He smoked half-an-ounce of “shag” daily and drank about four pints of beer. His sight had been failing for about two months. As is common in early stages of this disease the ophthalmoscope revealed no decided changes at the optic discs.
He passed the test of the Holmgren wools satisfactorily, proving that the usual vision was normal for colour, but failed at once with the pellet test.
Fig. 36.
The objects in view were to test his perception of the spectrum colours, and then the extent of his retinal field for colour. This last is not recorded here. The spectrum colours were reduced to uniform luminosity between λ 4600 and λ 6600. Diaphragms containing holes of different sizes were placed in front of the last prism, and thus a round spot of monochromatic light of the same luminosity was produced upon the screen when a slit was passed through the spectrum. From the red end to λ 5270 he called the whole of the colours white, and from that point he began to see blue, called the colours bluish and blue. When the full illumination for all the colours was used, the same results were obtained. From this examination it would appear that he was totally deprived of the sensation of any colour except of blue. A subsequent examination of his perception of the luminosity of different rays, however, has to be taken into account, for in the first examination he had no light of pure white with which to compare the colours. In the next experiments, a strip of white light was placed in juxtaposition to the colour, and the results were slightly different. The table below gives his luminosity measures ([Fig. 36]). Col. I. is the empyric scale number, II. is the wave-length, III. the luminosity of the colour to the normal eye, IV. the luminosity to X., and V. the ratios of III. to IV.
In the diagram, his luminosity curve X. is shown, its area being 1400 against 1650 for the normal eye. His central perception of light, as arrived at by the extinction method, was only two-thirds of that of the normal eye; hence his area of luminosity should be 1100. As it is 1400, the ordinates of the above curve should be multiplied by 0·8, to compare with that of the normal eye.
| I. | II. | III. | IV. | V. | Colours to X. | Spectrum colour to normal eye. |
| Scale No. | Wave- length. | Luminosity to the normal eye | Luminosity to X. | IV. — III. | ||
| 60 | 6730 | 7·3 | 0 | 0 | Sees only the white stripe | Red. |
| 57 | 6423 | 32 | 10 | 0·31 | Calls red yellowish, and white bluish | Scarlet. |
| 55 | 6242 | 65 | 38 | 0·65 | „ „ | |
| 53 | 6074 | 96 | 86 | 0·89 | Both one colour | Red-orange. |
| 51 | 5920 | 99 | 90 | 0·91 | „ „ | Orange-yellow. |
| 47 | 5660 | 92 | 83 | 0·90 | Calls green a little blue; white he sees as white | Greenish-yellow. |
| 43 | 5430 | 69 | 625 | 0·90 | „ „ | Yellowish-green. |
| 40 | 5270 | 50 | 46 | 0·92 | „ „ | Green. |
| 32 | 4910 | 8·5 | 9 | 1·06 | Sees blue as blue, and white yellowish | Greenish-blue. |
| 31 | 4960 | 7 | 8 | 1·14 | „ „ | Blue. |
| 26 | 4680 | 3 | 3 | 1·00 | „ „ | Blue. |
His readings of luminosity were made without any hesitation, and were concordant for each observation, which is not to be wondered at, as the matches, except at the blue end, were practically matches of different mixtures of black and white.
It appears that the white which X. sees as white is the same as the orange sodium light, and that the red he sees is yellowish. The mixture of this yellowish-white with the blue makes white. He sees a little blue in the spectrum colour at λ 5720, so it must be taken that at that point of the spectrum he begins to see colour—a point which is considerably lower than that given by his preliminary examination of the spectrum colour, and due, no doubt, to the fact that in this experiment he had the white light of the positive pole of the electric light to compare with it. It seems probable that what X. called yellowish was really a sensation of white mixed with a very small quantity of red sensation, for he saw no yellow in the orange, in which that colour would be most easily distinguished on account of its luminosity. Red light, when strongly diluted with white light, to the normal eye is often called orange.
As, practically speaking, the colour vision of X. is confined to blue and white, it is of interest to note the difference in luminosity at the different parts of the spectrum that is registered by him and by P., who had blue (violet) monochromatic vision. To facilitate the comparison, the luminosity curve of the latter is shown in the diagram.
Fig. 37.
The thin line curve is the normal curve.
Perhaps another case of a patient suffering from tobacco blindness may be quoted, as it will show the differences that exist in recognising the colours of the spectrum, and that the shorter the visible limit of the spectrum at the red end, the more pronounced is the extent of the colour blindness. G. suffered from a very well-marked tobacco scotoma, occupying a considerable area. His curve of luminosity of the spectrum is shown in [Fig. 37]. The horizontal band beneath will show the colours which the spectrum colours appeared to match.
Table of Luminosity for G. See [page 153].
| Scale No. | Wave- length. | Reading. | Colours named by G. | Colour of spectrum to the normal eye. |
| 57 | 6423 | 0 | Scarlet. | |
| 55 | 6242 | 3 | No colour | |
| 53 | 6074 | 11 | Colour “yellow,” white “blue” | Red-orange. |
| 51 | 5919 | 34 | „ „ „ „ | Orange-yellow. |
| 50 | 5850 | 60 | „ „ „ „ | |
| 49 | 5783 | 64 | Colour “gold,” white “sky-blue” | Yellow. |
| 45 | 5538 | 59 | ||
| 40 | 5270 | 40 | Both white | Green. |
| 35 | 5042 | 18 | „ | |
| 30 | 4848 | 10 | „ | |
| 29 | 4807 | 6 | Colour “very pale blue,” white as white | Blue. |
| 26 | 4707 | 4 | Colour “blue,” white “white” | |
| 20 | 4518 | 3 | „ „ „ „ | |
| 10 | 4248 | 2 | „ „ „ „ | Violet. |
G. was tested for light sense by the extinction method, and it appears that the final sensitiveness to light at the central part of the eye was nearly 12 times less than a person possessing normal sense. I may mention that I have examined one, if not two cases in which the patient was not only tobacco blind, but also congenitally colour blind. Though interesting for record, they need not be given in full here.
With these specimens of examination I must leave the cases of tobacco blindness. Although very important, they by no means constitute the sole cases of colour deficiency due to disease. I will give as an instance a case of loss of colour sensation due to progressive atrophy of both eyes which was examined, with Mr. Nettleship’s aid. When tested with spectrum colours—a patch of white light being placed in juxtaposition with the colour—it was found that W. S. was absolutely blind to colour from 26·75 (λ 4733) on the scale of the spectrum to the termination of the red of his spectrum, which was close to 63 on the scale (λ 7082). Above scale No. 26·75 W. S. saw blue, and his spectrum was continued normally in the violet. His luminosity curve ([Fig. 37]) was made without any difficulty, and, compared with my own, shows a slight deficiency in brightness from the red to the yellow, but his perception of luminosity increases as the blue is approached.
Table of Luminosity for W. S. See [page 155].
| Scale No. | Wave- length. | Reading. | Spectrum colours named by W. S. | Spectrum colours to normal eye. |
| 60 | 6728 | 3·4 | Grey | Scarlet. |
| 58 | 6520 | 15·0 | „ | |
| 56 | 6330 | 41·0 | „ | |
| 55 | 6242 | 43 | „ | |
| 54 | 6152 | 69 | ||
| 52 | 5996 | 94 | ||
| 50 | 5850 | 100 | „ | Orange. |
| 48 | 5720 | 96 | ||
| 45 | 5538 | 88 | ||
| 42 | 5373 | 74 | ||
| 40 | 5270 | 61·5 | „ | Green. |
| 38 | 5172 | 45 | ||
| 35 | 5042 | 30 | ||
| 30 | 4848 | 12 | „ | Blue. |
| 25 | 4675 | 6 | Bluish | |
| 20 | 4518 | 4 | ||
| 15 | 4376 | 3 | Blue | Violet. |
| 10 | 4248 | 2·5 | „ |
He was subsequently tested with colour discs—Ultra-marine (U), Red-royal (R), Emerald-green (G), Chrome-yellow (Y), White (W), and Black (B).
It was found that—
165 (U) + 48 (R) + 147 (G) = 75 (W) + 285 (B).
The black reflected 3·4 of white; hence the true equation is—
(i). 165 (U) + 48 (R) + 147 (G) = 84·7 (W) + 275 (B).
(ii). 120 (U) + 240 (Y) = 196 (W) + 164 (B) (corrected)—
With 260 (U) + 100 (Y) he sees blue.
250 (U) + 110 (Y) he sees light-blue.
242 (U) + 118 (Y) he sees no blue.
This last in connection with (ii) shows that his blue perception is neutralised by the yellow, although the yellow to him was matched with white.
I have already shown you a chart of the insensitive area of the retina found in a tobacco-blind case, and it may be advisable that you should see an example of the curtailment that exists, both for light and colour, in the field of vision of eyes in which there is progressive atrophy of the optic nerves. The large black area shows the part of the field that was encroached upon. The dark spots show small areas which are also insensitive. The field for colour shown by the inner shaded area is also encroached upon, and practically the patient was blind in a great part of his field. His form vision was also very bad, and his colour perception feeble. The three charts given in these lectures were brought by Mr. Nettleship, for the information of the Colour Vision Committee of the Royal Society, and by his permission they are reproduced here.
Fig. 38.
Left Eye.
Right Eye.
Two other cases I may give in some detail, one in which the sensation of colour is totally absent in the left eye, the right eye being normal; and the other in which there is colour blindness of a very rare character. The first case is that of a lady, whom we will call Miss W. It appears from the history of this lady that she had a slight stroke of paralysis which affected her left side, and that she subsequently found her left eye was deprived of all sensation of colour. It is said by the specialists who examined her retina that this is a case of atrophy of the optic nerve. She had very little difficulty in matching the most brilliant spectrum colours with the white patch of light. Her curve of luminosity is given in [Fig. 39] (see table, [page 228]). At 19 of the scale, which is well in the blue, she had very little sense of light, though her extinction curve shows that it extended to some distance beyond. The eye in which normal vision existed was, during the examination of the defective eye, bound up with a handkerchief, and when occasionally she was allowed to use both eyes, her astonishment was great to see the colours which she had matched with the white. The curve of luminosity taken with her right eye coincided with my own, which throughout we have taken as normal. From her extinction curve we gather that there was a marked diminution of sensitiveness to light in her left eye compared with that of normal vision. Apparently, in that eye she only has 1/25 of the normal sensitiveness to light near E in the green, but her extinction curve takes the same general form as that of the normal eye. The difference between the sets of ordinates of the two indicates the difference in sensitiveness for each part of the spectrum.
Fig. 39.
Her persistency curve as calculated occupies the same position and is of about the same dimensions, when the maximum is made 100, as that of the normal eye, as it is therefore of red- and green-blind, and also of the two cases of monochromatic vision. We have in Miss W. a type of colour blindness which no present theory of colour vision accounts for without straining; and it would probably have to refer it to the seat of sensation rather than to the retina alone.
Fig. 40.
The thin line curve is the curve of luminosity for the normal eye.
The second is a case of congenital colour blindness and with no trace of disease, brought by Mr. Nettleship to the same Committee. He found that this lady, N. W., mistook blue for red, and it was with some curiosity that this case was examined. Her first examination was as to colour sense with the spectrum colours, a patch of monochromatic light being placed in juxtaposition with an equal patch of white light. At 62·5 (λ 6890) of the scale the light of the spectrum disappeared. As the slit moved along the spectrum, and the white was approximately reduced to equal luminosity, she described all the red as grey, and of the same colour as the white until 53·5 (λ 6110). At this point she said the colour was brownish compared with the white, and this hue continued to her till 48 on the scale (λ 5720), when she said the colour was “neither brown nor green, but both.” From 48 on the scale she described the colour as green, when it changed quite suddenly at 31·5 (λ 4905). From this point and in the blue she again began to see grey; the grey at this end of the spectrum, and also of the white patch, she called brownish-grey. This name must evidently have been a mental distinction, as she described the red end and the white as grey only, and not brownish-grey; and, indeed, she was tested again over that part of the spectrum, and adhered to the previous naming. It would appear to be due to low luminosity, which made the grey appear to her what she called brownish, rather than to any actual difference in hue.
| Scale No. | Wave- length. | Reading. | Colours named by N. W. | Spectrum colours to normal vision. |
| 60 | 6728 | 3 | Both grey | Red. |
| 58 | 6520 | 10 | „ | |
| 56 | 6330 | 30 | „ | |
| 54 | 6152 | 52 | Colour “brownish,” white “grey” | |
| 52 | 5996 | 70 | „ „ „ | |
| 50 | 5850 | 81 | „ „ „ | Orange. |
| 48 | 5720 | 87 | Colour “brownish-green.” white “grey” | |
| 46 | 5596 | 90 | Colour “green,” white “grey” | |
| 44 | 5481 | 88 | „ „ | |
| 42 | 5373 | 82 | „ „ | |
| 40 | 5270 | 62·5 | „ „ | Green. |
| 38 | 5172 | 46 | „ „ | |
| 35 | 5042 | 23 | „ „ | |
| 32 | 4924 | 12·5 | „ „ | |
| 31 | 4886 | 10 | Colour “brownish-grey,” white “brownish-green.” | |
| 30·5 | 4862 | 8·5 | „ „ „ | Blue. |
| 25 | 4675 | 5 | „ „ „ | |
| 20 | 4518 | 3 | „ „ „ | |
| 15 | 4376 | 2·5 | „ „ „ | |
| 10 | 4248 | 1·5 | „ „ „ | Violet. |
| 0 | 4010 | 0·2 | „ „ „ |
Her curve of luminosity in the spectrum was next taken, and her readings are given in the table above. The curve is shown in [Fig. 40]. The shaded band beneath it applies to her curve. Miss W.’s luminosity curve is also repeated in the same figure for the sake of comparison.
An endeavour was made to form a series of colour equations with her eyesight by placing three slits in different parts of the spectrum, but without success, although a match with white was made in two positions. One slit was in the orange-red (52 of the scale), another at E, and the third at G; mixtures were made which she said matched the white, but they were so erratic that it was useless to measure the apertures. When the slit in the violet was covered up, a white patch being alongside as a comparison, she called the mixture of red and green “brownish-green”; when the slit in the red was covered she called the mixed light of green and violet “green”; and when the green slit was covered up she called the purple colour a “different kind of brown.”
When the first slit was moved into the red near the lithium line she called the colours “green,” whenever the green slit was uncovered. A piece of red glass was placed in the white reflected beam, forming a red patch, and a patch of the blue at scale No. 30·5 (λ 4862) was placed alongside, and she matched them in luminosity and in colour. (The dominant colour of the signal glass in question was λ 6220.) She finally was tested with colour discs.
To make white she required
130 G + 113 R + 117 U = 72 W + 218 B.
She was then tried with the blue and green discs alone and made a match—
258 U + 102 G = 65 W + 295 B.
An attempt was made to match with the green and red discs alone, but this failed.
She matched the red disc alone with black and white, and also the blue disc alone—
360 R = 56 W + 304 B (corrected),
360 U = 60 W + 300 B (corrected).
With any proportion of R and U mixed together she matched a grey of approximately the same intensity as above, as it might be supposed she would from the last two equations.
Taking the intensity curve of the light reflected from the red disc, it was found to contain a great deal of the part of the spectrum which she called brownish, viz., from 33·5 to 48 on the scale, whereas the blue reflected a trifle of this portion of the spectrum, as did also the green; and this may account for her making a match to grey of U and G, and not of R and G, but it is hard to see why she matched U alone and also R with the grey.
Reviewing the case, it seems that any perception of colour is very small, and that the sensations are green and much less red. From the equations it also seems that she would have matched green with white and black alone, and that 360 G = 75 W + 285 B. Perhaps the explanation of the matches and names of colours may be that a proportion of colour may be mixed with another without being perceived, but this colour so hidden has still the capability of neutralising a certain quantity of the complementary colour.