On the tests for muscular asthenopia and on insufficiency of the external recti muscles / Henry D. Noyes.

  • Noyes, Henry D. (Henry Drury), 1832?-1900.
Date:
[1884]
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Licence: Public Domain Mark

Credit: On the tests for muscular asthenopia and on insufficiency of the external recti muscles / Henry D. Noyes. 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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    the muscles to maintain; it is comfort in activity, not absolute relaxation. On the other hand equilibrium, as we ascertain it by various tests, whether it be by the vertical diplopia test of Graefe, or by the peculiar use of a prism when one eye is screened, which Alfred Graefe uses, or whether it be assumed to exist in some arbitrary relation between convergence and divergence, equilibrium of the visual axes, however ascertained, is not the same thing as repose of the muscles. Repose is the combined result of adequate power of accommodation, of muscular energy, and of cerebral and general function. It exists when work in near objects can be per- formed without irritation, fatigue or pain. When this is not the case we have asthenopia, and yet our tests may proclaim muscular equilibrium. Another pregnant observation grows out of the above remark viz. that we have no right to assume, that unless each one of the above three factors takes part in a given degree there either cannot be asthenopia or that there must be asthenopia. Facts disprove such a theoretical assumption. There may exist a great degree of muscular insufficiency as declared by tests, and no asthenopia be present. I indroduce one situation of such a kind, in which the externi would be accused, and in which no sign whatever of asthenopia existed. Case i. Dr. James L. M. aet 29. Physician. New-York. Examined \0. D. -4- 48c oo°v = 20/i2 without atropia has }Q g_ _j_ 3Qc QQov = 20/l8> There is no spasm of accommodation, The state of his muscles is as follows with correcting glasses at 20' adduction = 35°) 0 at 12 add. = 370) , 0 abduction = 5°j 40 abd. = 25°) with verti- v. d. = equilibrium, cal diplopia = 50 convergence. He never makes use of any glasses for any purpose, he uses his eyes abundantly, he never experiences any pain or inconvenience, either in reading or writing, or in the use of the microscope. In this person the normal state of A and the robust state of the central and peripheral nervous system neutralise the want of equilibrium, which is exhibited by vertical diplopia at 20 feet. Still another explanation is possible in such a case viz. that for this person a low angle of con- vergence for distance is the state of repose as distinguished from equili- brium. In him with hyperopic astigmatism some tension both of A and of muscles would be natural. Yet the absence of both accommodative and of muscular asthenopia seems to me most naturally to be explained by the want of excitability in, or rather, by the abundant and quiet vigor of the nervous force. It is doubtless true that for all persons the state of repose in the relations of the visual lines will not be identical: they may have for distant vision, parallel divergent or convergent axes. Doubtless for distant vision the normal state for emmetropic eyes is parallelism. For corrected ametropic eyes it should be the same, but variations arise through differences in the form of the skull affecting the shape of the orbits, through the varieties in the interpupillary distance, and through inherent differences in the capacity of the muscles. It is not however a safe assumption, in my opinion, to take for granted that a