Eyestrain (commonly called asthenopia) / by Ernest Clarke.

  • Ernest Clarke
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Eyestrain (commonly called asthenopia) / by Ernest Clarke. Source: Wellcome Collection.

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    Persons who cannot travel during the day with their backs to the engine or horses can do so with impunity at night, and hence the cause must be connected with the passage of objects seen from the carriage window. Our forward mode of progression familiarises us with the passage of objects towards us, but we are unfamiliar with the reverse, and this may be the cause of the symptoms. Again, the vertigo experienced by most people on looking down from a great height is probably another instance of this unfamiliarity. Looking upwards for a great distance produces no such effect, because we are perfectly familiar with the practice; and sailors and others who are accustomed to dizzy heights can generally look down with impunity, because the unfamiliarity has become familiar. Priestley Smith has suggested that the presence of latent deviation of the eyes may account for the giddi- ness, for the movements of the eyes downwards are usually associated with convergence, and the necessity for parallel vision may produce diplopia or a tendency to it. Brewer, in a paper on Apparent Movement of Objects associated with giddiness,^ refers to the giddiness produced by the eye trying to fix moving objects, as out of a railway carriage window. He says that if the eyes are not allowed to follow the moving objects then there is no giddiness, and if the image falls on the side of the retina there is no giddiness. He considers the giddiness is due to secondary apparent after-movements, and is an optical, and not a muscular, impression. Bain, on the other hand, considers that vertigo is always a motor symptom. Ross says diplopia causes the patient to become confused on endeavouring to grasp objects. This constant confusion ^ Trans. Oph. Soc.^ vol. ix., p. 176.