Things ophthalmic new and old / F. Fergus.

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

Licence: In copyright

Credit: Things ophthalmic new and old / F. Fergus. Source: Wellcome Collection.

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

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    the (jlasgow School of Medicine. To-night I would like to dwell upon some points which I consider of great importance as regards ophthalmology. In the first place, I wish to illustrate and emphasise what I have elsewhei’e indicated a.s the difference between visual acuteness and form sense. It is almost iiicredible that up to the days of my own teacher the late Professor Snellen, there had been no attempt to standardise visual acutene.ss, unless indeed we take such haphazard methods as the use of Jaeger’s hand types, which were the only types in use when I entered the Eve Infirmary as a student in 1879. Snellen’s t}'pes have become so universally used both on the Continent of Europe and in America that they are likely to be for many years to come the standard of visual acute- ness. It is quite true that the types of Landolt form a much more delicate test both for visual acuteness and as an ultimate proof of the accuracy of a refraction correction. Still, Snellen’s are so convenient and so easily used that id is not surprising to find that Landolt’s, although a much more refined test, have not as yet come into general use. I do not intend to say a single word to-night as to the accuracy of Snellen’s types. We accept them as a standard of visual acuteness of a definite kind, but at the same time it must be remembered that they are only an arbitrary standard, and by no means an absolute measurement. This fact constitutes the chief difficulty which we have in estimat- ing the working usefulness of an eye in terms of visual acuteness expressed in Snellen’s scale. To my own mind the problem is absolutely in.soluble, notwithstanding the very learned papers of Mr. Percival of Newcastle-on-Tyne and of; lilr. Berry of Edinburgh. If a patient reads the types at six! metres, which Snellen said should be .seen at six metres, then,] with a carele.ss use of language which is not in the least justifiable, he is said to have normal visual acutenes.s.j Snellen believed that to be the typically perfect, veiyi much as F'ahrenheit believed that the zero of his .scale was’ the lowest obtainable temperature. Snellen’s j is said to be! normal vision, and I fear that that phrase often gives rise in thought to the idea that that is the average for mankind.! Etymologically the word “normal” may mean a conformity' to a certain standard. That is not, however, the sense in which it is generally understood in this connection. Just a.s we say the normal temperature of the human bod}'is 98‘4, • meaning thereby that that is the average for healthy man- kind, so people are apt to understand when we say that the