The anomalies of the ocular muscles / by George T. Stevens.

  • Stevens, George T. (George Thomas), 1832-1921.
Date:
[1889?]
Catalogue details

Licence: Public Domain Mark

Credit: The anomalies of the ocular muscles / by George T. Stevens. Source: Wellcome Collection.

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    considered in respect to its importance, comparatively slight attention has been bestowed upon it in the litera- ture devoted to ocular affections. For the most important expositions in this department of ophthalmology we are indebted to Von Graefe, who left to the world, among his richest contributions to the literature of science, extensive memoirs upon subjects connected with the ocular muscles, replete with learning and original research. Investigators from his time have been, in large measure, content to ac- cept the results of his splendid genius as in the main con- clusive, and since his death it cannot be said that any very striking advance has been made in this direction. But Graefe's observations were those of a pioneer. They were not exhaustive, indeed they were, in respect to the class of affections now under consideration, incomplete and confined mainly, it may be said almost exclusively, to a single anom aly among several, and that one, as it will be seen, not the one of greatest practical importance. In these muscular affections in which, with absence of equilibrium the ability to maintain binocular vision remains, there is a tendency on the part of the eyes to permit the visual lines to deviate from parallel directions. Graefe, with others, taught that when the ocular muscles are all accurately pro- portioned in respect to their dynamic conditions, and the performance of binocular vision is accompanied with the least expenditure of energy, the ocular muscles are to be regarded as in equilibrium. The tests, however, which have been applied to the determination of the presence or absence of equilibrium have not in all cases been sufficiently trustworthy, and it is desirable in the beginning of this dis- cussion to determine precisely what is indicated by the term equilibrium, and to establish definite means of ascer- taining, by the most conclusive methods attainable, the true conditions of the muscles in this respect. Graefe regarded the ability to direct the axes of the two eyes to the same point, at the usual distance of reading, without excessive effort, as a practical standard of equi- librium, and taught that this should be gained even at the expense of very great loss of equilibrium at greater distan-