An endeavour to show that insufficiency of the internal recti muscles and myopia have been erroneously associated : and that the muscular asthenopia of myopia is not the result of such insufficiency, but of the anomaly of refraction / by Samuel Theobald.

  • Theobald, Samuel, 1846-1930.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: An endeavour to show that insufficiency of the internal recti muscles and myopia have been erroneously associated : and that the muscular asthenopia of myopia is not the result of such insufficiency, but of the anomaly of refraction / by Samuel Theobald. 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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    8. The amount of accommodation, which corresponds with the con- vergence, which this would necessitate He desires, however, owing to his myopia, only and is, therefore, compelled to suppress fifty years of age, however, the amount of actual accommodation, which he is capable of exercising, is reduced to y’^, and he, therefore, requires the whole of it in order to enable him to see distinctly at 8. There has been, from youth up, a gradual diminution of the amount which it was neces- sary for him to suppress, until now there is none remaining; and the parallelism between the effort of convergence and the effort of accommo- dation is at last complete. But, indeed, for the influence of the myopia, we would be presbyopic, and would require, in order to read at 8'^ convex spectacles. The myopia serves the purpose of the convex glasses how- ever, and presbyopia is, for a time, deferred. Tf it be true that the disproportion between accommodation and con- vergence in myopia is capable, in the earlier years of life especially, of exerting so potent an influence in promoting its increase, it becomes im- portant that in the treatment of progressive myopia our attention should be directed towards it, as a condition the elimination of which is of the greatest moment. Let us inquire in what way this elimination may be accomplished. As, under such circumstances, convergence is in excess of accommoda- tion, it is evident that, either by diminishing the extent of the former, while the latter remains constant, or by increasing the latter while the former is unchanged, equality between them may be restored. By means of prismatic glasses, we have it in our power to diminish the convergence to any desired extent; or we may increase accommodation and make it equal convergence by neutralizing the myopia by concave glasses. Prac- tically, however, the latter plan is not available except in the slighter de- grees of myopia ; because the tension of accommodation which it neces- sitates is itself found to be productive of mischief. “When the myopia is slight in reference to the range of accommodation, and the eye is other- wise healthy,” we may, nevertheless, resort to this method of correcting the disproportion, and thereby relieve the asthenopia, and favourably modify the progress of the myopia. We have the authority of Bonders for saying that under such circumstances “ neutralizing glasses may be worn as spectacles, and may be used even in reading and writing.” “ I think it is even desirable,” he adds, “that this should be done. When per- sons with moderate degrees of myopia have in youth accustomed them- selves to the use of neutralizing spectacles, the eyes are in all respects similar to emmetropic eyes, and the myopia is, under such circumstances, remarkably little progressive.” “ I am acquainted with numerous ex- amples of this even among those of my friends who have passed their lives in study.’” And, again, in speaking of insufficiency of the internal recti