The diseases of the eye / by Edward Nettleship.

  • Edward Nettleship
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: The diseases of the eye / by Edward Nettleship. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    is easier to obtain a very large scries in this material tlian iu any other. The manner in which a eolonr-bliud person behaves will often exeite suspicion of his defect. He will perliaps place doubtfully side by side with I, such a colour as No. 2 or 5, to see whether or not tbey arc alike, and finally will decide that they are not quite of the same colour, though rather alike. In such cases, and again iu others, where perhaps the patient does not understaiul what is wanted, the diagnosis may often be made certain iu the following manner :—Take two colours over which the patient is stumbling, or on which he cannot express himself, say Nos. Ila and a lighter shade of 9, add a third of the same dominant colour as 9, but of a markedly different shade, such as 10 or 12; now ask iiim which pair is more alike, Nos. 1I« and 9, or Nos. 9 and 10; if he says II« and 9 arc more alike he is colour-blind, and is judging of their similarity by the shade, that is the amount of white contained in each of them, and not by their colour. It is easy to vary this test according to the requirements of the case. Another good method is to tell the patient to pick out all the skeins of one colour, say green, without requiring him to match them precisely with any test skein; if decidedly colour- blind, he will conlidcntly select not only those which are green, but a number of others, usually the grey ones. Or we may say. Do you see any green skeins among tliem ? If colour-blind he will say No, or hesitate, or make the same mistakes as above. A special arrangement of the wools, enabling a quick, ac- curate and uniform record of colour perception to bo made, has been designed by Dr Wm. Thomson, of Philadelphia (' Trans. Amer. Oplith. Soc.,' 1880, p. 142). Of the many other tests for colour-blindness the following may be mentioned: Stilling's Tables (to be obtained through Williams and Nor- gate) consist of coloured letters or patterns printed on a ground- work of one of the confusion colours. They are preferred by some to Holmgren's wools. Bonders' method determines the colour-sense (or colour-defe(-t) quantitatively by means of a light of known intensity, which passes through a.]iertures filled by differently coloured glasses; these arc recognised at a specified distance if the colour-sense is normal. Mr Jeaffrcsou (of Newcastle) has lately constructed an in- genious ajjparatus in which the coloured wools, fixed in radii upon a rotating disc, can be successively brought opposite to stationary patches of the respective confusion colours, which are placed just l)cyond the cireunifercnec of the disc (' Lancet,' , July I7tli,'l88(i).
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