Colour vision

by Sir William de Wiveleslie Abney

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.