The action and uses of prismatic combinations / by Archibald Percival.

  • Percival, A. S. (Archibald Stanley), 1862-
Date:
[1881]
Catalogue details

Licence: Public Domain Mark

Credit: The action and uses of prismatic combinations / by Archibald Percival. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    image, and his chief trouble is his difficulty in recog- nising the position of objects, and even this is generally but a temporary one. But if his defect is slight, a diplopia may arise of the most annoying description, for two objects appear to exist, which are both clear and well defined, and which yet seem to overlap each other, owing to the fact that their imagcs are formed near the maculae, in those parts of the retinae in fact where vision is most distinct. There is, therefore, a very strong desire for fusion of these retinal images, and binocular vision is sometimes maintained by an excessive innervation of the affected muscles, which produces in its turn Symptoms of giddiness and head- ache, and these are generally associated with certain others of the neurasthenic type. If the muscular tcn- sion is relaxed even for a moment, double vision occurs, entailing a psychical perplexity which is no less distress- ing to the unfortunate sufferer. The Symptoms, then, of muscular asthenopia are most accentuated when the want of balance in the ocular muscles is slight, and prisms or prismatic com- binations would at first sight appear obviously the rational means of correcting all these muscular defects. Such indiscriminate treatment has, however, proved far from successful, and many Ophthalmie surgeons, dis- appointed with their results, have abandoned the use of prisms, and thrown discredit upon them. It is not unusual, indeed, now to hear operative measures advo- cated in the strongest terms for all cases. In the present paper I wish to point out some of the causes of failure, and to indicate those conditions in which we may reasonably hope for a successful issue by ordering prisms or prismatic combinations. The dis- repute into which they have fallen is due, I believe, very largely to an imperfect recognition (i) of their precise action ; (2) of the special conditions for which they may be appropriately prescribed. There are, however, still deeper causes at work also. The fundamental