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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    ces. Thus, in operating for relief of insufficiency of the interni, he was ready to induce very high degrees of insufficiency of the externi, or even homonymous di- plopia at a distance. As Graefe's operations were in large measure designed for the relief of insufficiency of the interni, in cases of high grades of myopia, the great disad- vantages of the loss of equilibrium at a distance were less pronounced than would have been the case under other circumstances. Such a standard of equilibrium should not be accepted. Equilibrium does not exist when compara- tively easy fusion of images is gained at one point at the expense of difficulty or impossibility of fusion at another. In equilibrium, the visual lines of the two eyes should be parallel when the force of the will in accommadating or adjusting the eyes is removed—that is, when the minimum of nervous impulse is directed to the ocular muscles. Devia- tions from a given standard of equilibrium short of the loss of power of fusion of images have been known as insuffi- ciencies. The term has, however, been mostly applied to an inadequate converging power for the distance of read- ing or ordinary work, and it has often, even by Graefe, been employed in connection with low grades of actual strabismus. In the conditions of absence of equilibrium now under consideration, and as they will be discussed in this paper, there is, in the act of vision, no actual turning of one visual line in a direction differing from that of the other when looking at a distant point. Indeed, in gazing directly fo'rward at a distant object parallelism is supposed. There is, however, in these conditions, on the part of some one or more muscles, a tendency to disturb the balance ; and should the nervous control be so removed as to permit of the consummation of this tendency, an actual deviation would result. Such irregular tendencies, then, may exist in as many directions as there are forces to induce irregular tension—that is, not only in as many directions as there are muscles to act, but in as many directions as the muscles may combine to act. In short, then, these tendencies may exist in all directions. Without stopping here to discuss