The refraction of the eye : a manual for students / by Gustavus Hartridge.

  • Gustavus Hartridge
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: The refraction of the eye : a manual for students / by Gustavus Hartridge. Source: Wellcome Collection.

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    equilibrium between the internal and external recti muscles. In the liypermetrope there is a want of harmony between the accommodation and the convergence, the two functions having to be used in unequal degrees; and when we correct his refraction with glasses he will have to use these two functions equally, or at least in different proportions from that to which he has been accustomed. Many people are able at once to accommodate themselves to this new state of affairs; but there are others in whom the force of habit is so strong, that they cannot thus throw off the acquired habit of using the accommo- dation in excess of the convergence. You must not, therefore, be discouraged if occasionally your patient is not at once and completely relieved of his asthe- nopia, as soon as you have given him convex spec- tacles. A fortnight's trial should be made before we can decide that such spectacles will not relieve the patient of his asthenopia. Asthenopia depends much upon the nervous sys- tem of the individual; in some a very slight amount of astigmatism will produce accommodative asthe- nopia ; one hypermetrope will have no uncomfortable feelings, while another, whose condition seems exactly similar, will suffer much, so that it is essential to attend to the patient's general health and nervous system. Muscular Asthenopia is most frequently due to myopia, though it occasionally occurs in emmetropia or even hypermetropia; it is characterised by the