Address / by Freeland Fergus, M.D., F.F.P.S.G., F.R.S.E., President, delivered before the Society on 4th November, 1908, at the opening of Session 1908-1909.

  • Fergus, A. Freeland (Andrew Freeland), 1858-1932.
Date:
1908
Catalogue details

Licence: In copyright

Credit: Address / by Freeland Fergus, M.D., F.F.P.S.G., F.R.S.E., President, delivered before the Society on 4th November, 1908, at the opening of Session 1908-1909. Source: Wellcome Collection.

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    Let us briefly illustrate what is meant by visual acuteness. If anyone take a page of print and look at a word about the centre of the page he will at once observe that while he looks steadfastly at the selected word he is unable to see almost any other word on the same page at the same moment; possibly if there are one or two small words in juxtaposition he will be able to make out those immediately next to. the one which he has selected, but the rest of the page will be to him at the moment entirely illegible. As is wrell known this function which we have called visual acuteness is the special property of that part of the retina which is known as the macula lutea and extends to only a very small angle round the point of fixation. It is commonly called the form sense, which seems to me in great part a misnomer, for, if a person look at one part of a wrall he will be at the same time aware of the form of objects placed at a considerable distance from his fixation point. Thus, to take a concrete example, if any member of my audience gaze fixedly at the chair placed im¬ mediately behind me, he will be conscious at the same time that the clock high up on the wall is circular. He will also be aware of the shapes of many other objects situated in the. room. Probably this faculty depends upon the light sense rather than on the visual acuteness, but still the fact remains that the sense of form in this wider acceptation of the term, belongs to the entire field of vision and is not restricted to the area of the macula. I prefer to use the definite term visual acuteness for that special function of the macula by wThich mankind is enabled to read small type and probably also to write. So far as the eye is concerned, it depends on the macula lutea, and there is every reason to believe that certain portions of the occipital cerebral cortex have to do with this special function. Further, there is much evidence to prove that unless the visual acuteness is developed in early life it remains in abeyance. It is a matter of common notoriety that if in the first two or perhaps even three years of life a child begins to squint constantly with the same eye, that when maturity comes it will be found that the squinting eye is possessed of almost no visual acuteness at all. Bonders of Utrecht was amongst the first to point out this fact and to emphasise it. He called this want of vision in the squinting eye amblyopia exanopsia, by which he meant blindness from wrant