A practical treatise on diseases of the eye / by Édouard Meyer ; tr. with the assistance of the author, from the 3rd French ed., with additions as contained in the 4th German ed. by Freeland Fergus.

Édouard Meyer

Date:: 1887

Credit: A practical treatise on diseases of the eye / by Édouard Meyer ; tr. with the assistance of the author, from the 3rd French ed., with additions as contained in the 4th German ed. by Freeland Fergus. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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$III. Examination of the Retinal Sensibility in General.— In a certain number of cases—for example, when an opacity of the lens prevents the light from striking the retina—the examination of the retinal sensibility cannot be made by the method which we have explained. And yet this examination is in these cases an absolute necessity. Formerly, indications of the state of the retina as regards its sensi- bility were sought exclusively in the reaction of the pupil to light, because the pupil reacts more slowly, or not at all, when the sensibility of the retina is diminished or destroyed. Fig. 21. PRIESTLEY SMITH'S PERIMETER. Another method of examination consisted in the observation of luminous apparitions provoked by steady pressure on the external portions of the eyeball. These apparitions, to which the term phosphenes has been applied, are very readily produced when we rub lightly with the distal phalanx of the small finger, with the rounded end of a pencil, or with a pen- holder, on several points of the eyeball through the lids. During this rubbing, the patient is asked to look to the side opposite and ai show two forms of self-registering perimeter—an instrument of (real utility. I he figures, with a description of each, are to he found in I.andois and Stirling's l'li\ ftiolog] 11 '<\ iffin .\ i -.; -', v-.i. ii, pp. i i iiese instruments are to be had from Pickard& Currie, Lorn$