Things ophthalmic new and old / by A. Freeland Fergus.

  • Fergus, A. Freeland (Andrew Freeland), 1858-1932
Date:
[1913?]
Catalogue details

Licence: In copyright

Credit: Things ophthalmic new and old / by A. Freeland Fergus. Source: Wellcome Collection.

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    Departmental Committee of the Board of Trade on Sight Tests, it was a distinction which seemed to be entirely new to the members of the Committee, for all their witnesses and all the members of Committee always spoke of the form sense as synonymous with visual acuteness. The two must be carefully distinguished. Visual acuteness is a function of the macular area only; it is that power by which we read and write and distinguish visually such things as music score. That is all that I mean by visual acuteness. Let me just recall an experiment which I have often shown to classes of students, and to which I directed the attention of the Committee of the Board of Trade. If a person look at a word in the middle of a page of writing he will see the word, and possibly a few letters in its immediate neighbourhood; the rest of the page he will be quite unable to decipher. Just for a little space round the word at which he is looking he will clearly see letters, but on no other part of the page, unless he change the point of fixation. That is visual acuteness. While, however, he is looking at the original fixation point steadily he also can discern quite distinctly the forms of all other objects in his immediate neighbourhood. He can see various articles of furniture. He might see that there are persons in the same apartment. He can tell quite well perhaps whether those persons are men or women, although he cannot recognise them. The power of recognition also probably depends upon visual acuteness. That illustrates what I mean by the form sense. It is this form sense which is the important function of vision for most kinds of manual employment, and which is also chiefly used in such occupations as navigation. Take, for example, a man hewing stone. If he wishes to examine the texture of the stone as a geologist would do, he will require to use his visual acuteness. If he is merely distinguishing it from other material, such as the earth and clay, from which he is getting it, then the visual acuteness is probably not used at all; it is entirely that which I call form sense. A radical blunder is made when we attempt to express the working power of any man, so far as vision is concerned, in terms of visual acuteness. Working power, at anyrate, for manual employment has very little, if anything, to do with visual acuteness; it has to do with this form sense, or, as I prefer to call it, difference of back-ground sense. Herein is just the mistake which has been made by the recent Departmental Committee of the Board of Trade. They say, in spite of all facts to the contrary, that unless a man has got visual
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