330 Report of the Committee on Colour-Vision. 



u smalt." [The witness here handed in a number of charts illustra- 

 tive of cases of tobacco amblyopia, and atrophy of the optic 

 nerves, and explained with reference to them.] 



Question — They do not lose the sense of form, only the 

 colour ? — The test is used only for its colour. The form of the 

 spot is not spoken of, and is of no importance. 



Question — Is not the defect of Colour-vision generally accom- 

 panied by defect of Form-vision ? — Yes, always. I have never 

 seen a case in which the loss has been entirely a colour loss. 

 The form loss (loss of acuteness of vision at the centre of the 

 field) is always recorded first. Speaking broadly, the loss of 

 form-sense, as it is commonly tested, i.e., by black letters on a 

 white ground, is about proportionate to the loss of colour-sense at 

 the centre of the field. One commonly records the form-sense, 

 however, only at the exact centre of the field, whilst in the 

 cases of central (or approximately central) scotoma, one tests the 

 loss of colour-perception over an area extending several degrees 

 from the centre in every direction. If the scotoma area be re- 

 presented as a cloud, we shall have to say that in different cases 

 the total area of the cloud varies, as well as its average density, 

 and that its nucleus or densest spot, though always very near to 

 the exact centre of the field, seldom coincides precisely with that 

 point, being- usually 2 or 3 degrees to its outer (temporal) side, 

 sometimes inclined upwards, sometimes downwards. The cloud 

 usually forms an oval, extending further into the outer than the 

 inner part of the field, and frequently including the blind spot. 

 If the cloud be very large it may be co-extensive with the field 

 for green or for red, and then those colours will not be recognised 

 anywhere ; but in the ordinary tobacco cases the cloud is smaller 

 than the red field, if not smaller than the green field, so that a 

 red-perceiving zone is left of greater or less width and perfection. 

 (Several of the charts illustrate these various points.) In the 

 cases to which I have referred the patient has come for advice 

 on account of defect of Form-vision, and has seldom said anything* 

 about Colour-vision. One of the first complaints made is often of a 

 mistiness that prevents the patient from recognising the features 

 of a person at a distance (the scotoma when small covering the 

 person's face at a distance), and at the same time of difficulty in 

 reading, which is not removed by spectacles. Occasionally they 

 will say that people's faces look unnaturally pale. I have known 

 two cases in which sportsmen found out the defect whilst very 

 slight by their bad shooting : they could see the birds rise 

 (eccentric vision) but just when they aimed the bird " was lost." 



Question — When you have had a man who could not see red, 

 and have shown him a red object, say a bit of sealing wax, what 

 does it look like to him? — In accordance with what has been 

 already said this will depend largely upon (1) the size and (2) the 

 brightness (saturation) of the test object. If it be three or four 

 inches long, and an inch or so wide, he will (unless very bad) 

 usually recognise the colour, either because some part of its 



