Physical diagnosis : a guide to methods of clinical investigation / by G.A. Gibson and William Russell.

Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: Physical diagnosis : a guide to methods of clinical investigation / by G.A. Gibson and William Russell. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    If extending cliiefly to the outer side of the fixing-point, and corresponding to (i.e., subtending) that part of the retina between the optic disc and macula, known as the papUlo- macular area, the case is almost certainly one of toxic ambly- opia, due to the abuse of tobacco, and perhaps alcohol. Betrobulbar neuritis usually affects only one eye, while toxic amblyopia commonly, if not always, affects both, and the scotoma is symmetrical. The test should be made with red and green, for blue and yellow are generally well perceived, except in severe cases. It should be borne in mind that congenital colour blindness affects from two per cent, to three per cent, of the male popu- lation of this country, and a less proportion of females. It is commonest for red and green, but may be dis- tinguished from the foregoing by the fact that per se it in no way affects the direct visual acuity for form as tested, e.g., by Snellen's types. If, however, in a congenitally colour blind person from any cause the form sense has been rendered defective, a proper diagnosis might still be made by remembering that con- genital colour bhndness affects the whole field, while in the above affections, if uncomplicated, good colour perception is retained beyond the limits of the scotoma. With this simple apparatus the various forms of hemi- anopsia, if approximately complete in extent, may be also readily diagnosed, and practically it is only when we wish to determine precisely the state of the peripheral parts of the fields for different colours, or require a permanent record, that we need have recourse to perimetry, Fhosphenes.—This term is applied to the visual sensations induced by mechanical stimulation of the retina,—e.gr., the pressure of the tip of the Httle finger on the outer side of the globe occasions the sensation of a bright crescent with a dark centre in the inner part of the field. In an intelligent individual it is possible to make use of this as a test of the retinal capacity for stimulation when from any cause it is not possible to see the fundus clearly.