Licence: Public Domain Mark
Credit: Eyestrain (commonly called asthenopia) / by Ernest Clarke. Source: Wellcome Collection.
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Licence: Public Domain Mark
Credit: Eyestrain (commonly called asthenopia) / by Ernest Clarke. Source: Wellcome Collection.
![objects becoming indistinct, wavering, or double. This is certainly not my experience. Patients suffering from muscular asthenopia very often volunteer the remark that they ''see doubled Very often this diplopia is only temporary, for the very good reason that the cause is removed by the patient. In convergence insufficiency, if the work is too near, the effort of the internal recti to preserve binocular vision is so great that the muscles refuse to work at such high pressure any longer; the result is diplopia, with the inevitable necessity on the part of the patient to suspend work. Sometimes the lesser symptoms, viz., pain and headache, cause the patient to cease work before diplopia arises. Alfred Graefe, writing in 1880, says : Die betreffenden Individuen koennen sich nur kuerzere Zeit mit nahe liegenden Objecten (Lesen, Schreiben, etc.) ohne Gene beschaeftigen, dann erscheinen dieselben plotzlich doppelt, Zeilen und Buchstaben laufen wirr in einander, waehrend gleichzeitig ein Gefuehl des unbehagens oder schmertz- haften Zvvanges auf beiden oder vorzugsweise auf einem Auge lastet. ^ The double vision causes a retinal confusion ; this confusion produces on the individual a sense of want of equilibrium, causing vertigo and, if prolonged, sickness, vomiting, dyspepsia, palpitation and dyspnoea. Everyone is familiar with the giddiness produced by gazing at a pronounced check pattern, or looking through a stereo- scope or glasses that do not suit the sight; and many people are unable to travel during the day with their backs to the engine on account of the feeling of sickness that is induced.^ In both cases it is the unfamiliar retinal confusion that causes the trouble. 1 Graefe Saemisch Hdbh., bd. vi., p. 192. * See ]). 39.](https://iiif.wellcomecollection.org/image/b20395747_0030.jp2/full/800%2C/0/default.jpg)
