Anomalies of the ocular muscles. Fourth paper. [VII. An examination of Von Graefe's doctrine of 'antipathy to single vision'] / by George T. Stevens.

  • George Thomas Stevens
Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: Anomalies of the ocular muscles. Fourth paper. [VII. An examination of Von Graefe's doctrine of 'antipathy to single vision'] / by George T. Stevens. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    but desirable. This proceeding of making a correction of squint by a single operation has been supposed to be sus- tained by the theory that the muscle of the squinting eye is pathologically shortened to a considerably greater extent than its antagonist. It may be conceded that there is, within certain limits of unequal tensions of accordant muscles, a possibility of union of images; otherwise binocular vision would in no case be established except when exact balancing of the tension is secured. That easy and permanent associated action is com- patible with any considerable degree of diversity of tension, I do not believe. It may be objected that if this proposition is correct the proportion of perfect corrections for squint by the prevailing methods of operating must be less than is ordinarily sup- posed. It is probable that examinations made by methods more exact than those which have been ordinarily employed would show that a very large proportion of cases in which binocular vision has been presumed to have been established by the ordinary squint operation is much smaller than is commonly supposed. However this may be, whether the results of the standard squint operation is often successful or not, it is certain that such unequal tensions are in many instances incompatible with a blending of the images. A second causative influence, and one which acts as an element in nearly all of these cases, is the difference in rela- tive tension of muscles which act in the vertical direction. The instinct of bringing images to the same horizontal plane appears to be very great and only second, if indeed it is second, to that of union of images. In case of double images, whatever the difficulty of blending may be, the patient instinctively exerts his best endeavors to place the images in the same horizontal plane. It thus happens, that in certain cases in which, either with or without slight lateral inequality of tension, the effort to bring images to the same plane induces a lateral squint,—a squint which may be vari- able ; that is, such a squint may at one period of life be converging, and at another diverging. Thus, in a case now under my observation, the patient was, during her child-
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