The management of the eye, ear, and throat / by Henry Power, George P. Field, John S. Bristowe.

  • Power, H. (Henry), 1829-1911.
Date:
[between 1890 and 1899?]
Catalogue details

Licence: Public Domain Mark

Credit: The management of the eye, ear, and throat / by Henry Power, George P. Field, John S. Bristowe. Source: Wellcome Collection.

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    centre is noted. The same proceeding is practised from the opposite side, and the number again noted. The arc is now rotated to the vertical position, one arm stretching over the head, the other under the chin, and the disc again brought forward, and the degree noted. By repeating this proceeding with a series of intermediate positions, a kind of map or plan can be obtained, which shows that our field of vision extends from side to side, the eye remaining im- movable, about 140°, and that from above downwards it extends over 120°. A considerable portion of the field of vision of one eye is, however, covered by the other, so that the area in view, when the two eyes are open simultaneously, is not much more than 180° in extent. By rolling the eyes outwards, the head remaining immovable, some 80° more may be added; and if the head itself be rotated, the whole circle may be completed. It is rather curious to find that, although the eyes of short-sighted persons are often large and prominent, their field of vision is considerably less than in long-sighted persons, in whom the eyes are usually small and less prominent. Strictly speaking, we only appreciate degrees of light and colour with the eye ; and although it is generally considered that with our eyes, and our eyes alone, we can, in addition, distinguish size, form, motion, and relative position of objects, this is only in a certain sense true, for a rigorous examination of the mode in which our conceptions of size and form and motion are formed demonstrates that the im- pressions made upon the retina are materially aided by those of other senses, and especially by those of touch. The blind man to whom sight is given by the removal of a cataract